NuttxUserGuide.html

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<TITLE>NuttX Users Manual</TITLE>
<META NAME="AUTHOR" CONTENT="Gregory Nutt">
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<center><h1><i>Under Construction</i></h1></center>
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<CENTER><BIG><B>
NuttX Operating System
<P>
User's Manual
</B></BIG>
<P>
<SMALL>by</SMALL>
<P>
Gregory Nutt
<P>
<SMALL>Last Update: March 21, 2007</SMALL>
</CENTER>

<H1>1.0 <A NAME="Introduction">Introduction</A></H1>

<P>
This user's manual is divided into three sections plus a index:
<UL>
<LI><B>Section 1.0, <A HREF="#Introduction">Introduction</A></B>:
This section provides an overview of the NuttX user's manual.
<LI><B>Section 2.0, <A HREF="#OS_Interfaces">OS Interfaces</A></B>:
This section details the  interfaces provided by NuttX from the
perspective of the firmware developer.  This section is divided
into several paragraphs that describe different groups of OS interfaces:
<UL>
<LI>Paragraph 2.1 <A HREF="#Task_Control">Task Control Interfaces</A>
<LI>Paragraph 2.2 <A HREF="#Task_Schedule">Task Scheduling Interfaces</A>
<LI>Paragraph 2.3 <A HREF="#Task_Switch">Task Switching Interfaces</A>
<LI>Paragraph 2.4 <A HREF="#Message_Queue">Named Message Queue Interfaces</A>
<LI>Paragraph 2.5 <A HREF="#Semaphores">Counting Semaphore Interfaces</A>
<LI>Paragraph 2.6 <A HREF="#Watchdogs">Watchdog Timer Interfaces</A>
<LI>Paragraph 2.7 <A HREF="#ClocksNTimers">Clocks and Timers</A>
<LI>Paragraph 2.8 <A HREF="#Signals">Signal Interfaces</A>
<LI>Paragraph 2.9 <A HREF="#Pthread">Pthread Interfaces</A>
<LI>Paragraph 2.10 <A HREF="#FileSystem">Filesystem Interfaces</A>
</UL>
<LI><B>Section 3.0, <A HREF="#Data_Structures">OS Data Structures</A></B>:
This section documents the data structures that are used at the NuttX
interface.
<li><a href="#index">Index</a></li>
</ul>
<HR>

<H1>2.0 <A NAME="OS_Interfaces">OS Interfaces</A></H1>

<P>
This section describes each C-callable interface to the NuttX
Operating System. The description of each interface is presented
in the following format:
<P>
<B>Function Prototype:</B> The C prototype of the interface function
is provided.
<P>
<B>Description:</B> The operation performed by the interface function
is discussed.
<P>
<B>Input Parameters:</B> All input parameters are listed along
with brief descriptions of each input parameter.
<P>
<B>Returned Values:</B> All possible values returned by the interface
function are listed. Values returned as side-effects (through
pointer input parameters or through global variables) will be
addressed in the description of the interface function.
<P>
<B>Assumptions/Limitations:</B> Any unusual assumptions made by
the interface function or any non-obvious limitations to the use
of the interface function will be indicated here.
<P>
<B>POSIX Compatibility:</B> Any significant differences between the
NuttX interface and its corresponding POSIX interface will be noted
here.
<P>
NOTE: In order to achieve an independent name space for the NuttX
interface functions, differences in function names and types are
to be expected and will not be identified as differences in these
paragraphs.
<HR>

<H2>2.1 <A NAME="Task_Control">Task Control Interfaces</A></H2>

<p>
  <b>Tasks</b>.
  NuttX is a flat address OS.  As such it does not support <i>processes</i>
  in the way that, say, Linux does.
  NuttX only supports simple threads running within the same address space.
  However, the programming model makes a distinction between <i>tasks</i>
  and <i>pthreads</i>:
</p>
<ul>
  <li><i>tasks</i> are threads which have a degree of independence
  <li><a href="#Pthread"><i>pthreads</i></a> share some resources.
</ul>
<p>
  <b>File Descriptors and Streams</b>.
  This applies, in particular, in the area of opened file descriptors and streams.
  When a task is started using the interfaces in this section, it will be created
  with at most three open files.
</p>
</p>
  If CONFIG_DEV_CONSOLE is defined, the first three file descriptors (corresponding
  to stdin, stdout, stderr) will be duplicated for the the new task.
  Since these file descriptors are duplicated, the child task can free close
  them or manipulate them in any way without effecting the parent task.
  File-related operations (open, close, etc.) within a task will have no effect
  on other tasks.
  Since the three file descriptors are duplicated, it is also possible to perform
  some level of redirection.
</p>
<p>
  pthreads, on the other hand, will always share file descriptors with the parent
  thread.  In this case, file operations will have effect only all pthreads the
  were started from the same parent thread.
</p>
<p>
  The following task control interfaces are provided by Nuttx:
</p>
<ul>
  <li><a href="#taskcreate">2.1.1 task_create</a></li>
  <li><a href="#taskinit">2.1.2 task_init</a></li>
  <li><a href="#taskactivate">2.1.3 task_activate</a></li>
  <li><a href="#taskdelete">2.1.4 task_delete</a></li>
  <li><a href="#exit">2.1.5 exit</a></li>
  <li><a href="#taskrestart">2.1.6 task_restart</a></li>
  <li><a href="#getpid">2.1.7 getpid</a></li>
</ul>

<H3><a name="taskcreate">2.1.1 task_create</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
   #include &lt;sched.h&gt;
   int task_create(char *name, int priority, int stack_size, main_t entry, const char *argv[]);
</PRE>

<P>
<B>Description:</B> 
   This function creates and activates a new task with a
   specified priority and returns its system-assigned ID.
</p>

<P>The entry address entry is the address of the &quot;main&quot;
   function of the task.
   This function will be called once the C environment has been set up.
   The specified function will be called with four arguments.
   Should the specified routine return, a call to exit() will automatically be made.
</P>
<p>
   Note that an arbitrary number of arguments may be passed to the
   spawned functions.  The maximum umber of arguments is an OS
   configuration parameter (<code>CONFIG_MAX_TASK_ARGS</code>).
</p>
<p>
   The arguments are copied (via <code>strdup</code>) so that the
   life of the passed strings is not dependent on the life of the
   caller to <code>task_create()</code>.
</p>
<p>
   The newly created task does not inherit scheduler characteristics
   from the parent task:  The new task is started at the
   default system priority and with the SCHED_FIFO scheduling
   policy.  These characteristcs may be modified after the new
   task has been started.
</p>
<p>
   The newly created task does inherit the first three file
   descriptors (corresponding to stdin, stdout, and stderr) and
   redirection of standard I/O is supported.
</p>
<P>
<B>Input Parameters:</B> 
  <UL>
    <LI><I>name</I>. Name of the new task</LI>
    <LI><I>priority</I>. Priority of the new task</LI>
    <LI><I>stack_size</I>. size (in bytes) of the stack needed</LI>
    <LI><I>entry</I>. Entry point of a new task</LI>
    <LI><I>argv</I>. A pointer to an array of input parameters.  Up to
       <code>CONFIG_MAX_TASK_ARG</code> parameters may be provided.
       If fewer than <code>CONFIG_MAX_TASK_ARG</code> parameters are
       passed, the list should be terminated with a NULL argv[] value.
       If no parameters are required, argv may be NULL.
  </UL>
<P>
  <B>Returned Values:</B> 
</P>
<UL>
<LI>
  Returns the non-zero task ID of the new task or
  ERROR if memory is insufficient or the task cannot be
  created (errno is not set).
</LI>
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>POSIX Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following similar interface:
<PRE>
   int taskSpawn(char *name, int priority, int options, int stackSize, FUNCPTR entryPt,
                 int arg1, int arg2, int arg3, int arg4, int arg5,
                 int arg6, int arg7, int arg8, int arg9, int arg10);
</PRE>

<P>
  The NuttX task_create() differs from VxWorks' taskSpawn() in the
  following ways:
</p>
<UL>
<LI>Interface name
<LI>Various differences in types of arguments
<LI>There is no options arguement.
<LI>A variable number of parameters can be passed to a task (VxWorks supports ten).
</UL>

<H3><a name="taskinit">2.1.2 task_init</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
   #include &lt;sched.h&gt;
   STATUS task_init(_TCB *tcb, char *name, int priority, uint32 *stack, uint32 stack_size,
                    maint_t entry, const char *argv[]);
</PRE>

<P>
<B>Description:</B>
<P>
  This function initializes a Task Control Block (TCB)
  in preparation for starting a new thread.  It performs a subset
  of the functionality of <code>task_create()</code> (see above).
</P>
<P>
  Unlike task_create(), task_init() does not activate the task.
  This must be done by calling task_activate().
</P>
<P>
<B>Input Parameters:</B> 
  <UL>
    <LI><I>tcb</I>. Address of the new task's TCB
    <LI><I>name</I>. Name of the new task (not used)
    <LI><I>priority</I>. Priority of the new task
    <LI><I>stack</I>. Start of the pre-allocated stack
    <LI><I>stack_size</I>. size (in bytes) of the pre-allocated stack
    <LI><I>entry</I>. Entry point of a new task
    <LI><I>argv</I>. A pointer to an array of input parameters.  Up to
       <code>CONFIG_MAX_TASK_ARG</code> parameters may be provided.
       If fewer than <code>CONFIG_MAX_TASK_ARG</code> parameters are
       passed, the list should be terminated with a NULL argv[] value.
       If no parameters are required, argv may be NULL.
  </UL>
</p>
<P>
<B>Returned Values:</B> 
</p>
<UL>
  <LI><P>OK, or ERROR if the task cannot be initialized.</P>
  <P>This function can only failure is it is unable to assign
    a new, unique task ID to the TCB (errno is not set).</P>
</UL>
<P>
<B>Assumptions/Limitations:</B>
<UL>
<LI>task_init() is provided to support internal OS functionality.  It is
<B>not recommended</B> for normal usage.  task_create() is the preferred
mechanism to initialize and start a new task.
</UL>
<P>
<B>POSIX Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following similar interface:
<PRE>
   STATUS taskInit(WIND_TCB *pTcb, char *name, int priority, int options, uint32 *pStackBase, int stackSize,
                   FUNCPTR entryPt, int arg1, int arg2, int arg3, int arg4, int arg5,
                   int arg6, int arg7, int arg8, int arg9, int arg10);
</PRE>

<P>
  The NuttX task_init() differs from VxWorks' taskInit() in the
  following ways:
</p>
<UL>
<LI>Interface name
<LI>Various differences in types or arguments
<LI>There is no options argument.
<LI>A variable number of parameters can be passed to a task (VxWorks supports ten).
</UL>

<H3><a name="taskactivate">2.1.3 task_activate</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    STATUS task_activate( _TCB *tcb );
</PRE>

<P>
<B>Description:</B> This function activates tasks created by task_init().
Without activation, a task is ineligible for execution by the
scheduler.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>tcb</I>. The TCB for the task for the task (same as the
task_init argument).
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>OK, or ERROR if the task cannot be activated (errno is not set).
</UL>

<P>
<B>Assumptions/Limitations:</B>
<UL>
<LI>task_activate() is provided to support internal OS functionality.  It is
<B>not recommended</B> for normal usage.  task_create() is the preferred
mechanism to initialize and start a new task.
</UL>
<P>
<B>POSIX Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following similar interface:
<PRE>
    STATUS taskActivate( int tid );
</PRE>

<P>
  The NuttX task_activate() differs from VxWorks' taskActivate() in the
  following ways:
</p>
<UL>
<LI>Function name
<LI>With VxWork's taskActivate, the pid argument is supposed to be
the pointer to the WIND_TCB cast to an integer.
</UL>

<H3><a name="taskdelete">2.1.4 task_delete</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    STATUS task_delete( pid_t pid );
</PRE>

<P>
<B>Description:</B> This function causes a specified task to cease
to exist -- its stack and TCB will be deallocated. This function
is the companion to task_create().
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>pid</I>. The task ID of the task to delete. An ID of
zero signifies the calling task.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>OK, or ERROR if the task cannot be deleted.
This function can fail if the provided pid does not correspond to a task (errno is not set)
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
task_delete() must be used with caution:  If the task holds resources
(for example, allocated memory or semaphores needed by other tasks), then
task_delete() can strand those resources.
<P>
<B>POSIX Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following similar interface:
<PRE>
    STATUS taskDelete( int tid );
</PRE>

<P>
  The NuttX task_delete() differs from VxWorks' taskDelete() in
  the following ways:
</p>
<UL>
<LI>No support is provided for calling the tasks deletion routines
(because taskDeleteHookAdd() is not supported).
<LI>Deletion of self is not supported.  Use _exit();
</UL>

<H3><a name="exit">2.1.5 exit</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    void exit( int code );

    #include &lt;nuttx/unistd.h&gt;
    void _exit( int code );
</PRE>

<P>
<B>Description:</B> This function causes the calling task to cease
to exist -- its stack and TCB will be deallocated.  exit differs from
_exit in that it flushs streams, closes file descriptors and will
execute any function registered with atexit().
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>code</I>. (ignored)
</UL>

<P>
<B>Returned Values:</B>  None.

<P>
<B>Assumptions/Limitations:</B> 

<P>
<B>POSIX Compatibility:</B> This is equivalent to the ANSI interface:
<PRE>
    void exit( int code );
</PRE>
And the unix interface:
<PRE>
    void _exit( int code );
</PRE>

<P>
  The NuttX exit() differs from ANSI exit() in the following ways:
</p>
<UL>
<LI>The <I>code</I> parameter is ignored.
</UL>

<H3><a name="taskrestart">2.1.6 task_restart</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    STATUS task_restart( pid_t pid );
</PRE>

<P>
<B>Description:</B> This function &quot;restarts&quot; a task.
The task is first terminated and then reinitialized with same
ID, priority, original entry point, stack size, and parameters
it had when it was first started.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>pid</I>. The task ID of the task to delete. An ID of
zero signifies the calling task.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>
  OK, or ERROR if the task ID is invalid or the task could
  not be restarted.
  This function can fail if:
  (1) A pid of zero or the pid of the calling task is provided (functionality not implemented)
  (2) The pid is not associated with any task known to the system.
</LI>
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>POSIX Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following similar interface:
<PRE>
    STATUS taskRestart (int tid);
</PRE>

<P>
  The NuttX task_restart() differs from VxWorks' taskRestart() in the following ways:
</p>
<UL>
<LI>Restart of the currently running task is not supported.
<LI>The VxWorks description says that the ID, priority, etc. take
the value that they had when the task was <I>terminated</I>.
</UL>

<H3><a name="getpid">2.1.7 getpid</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;unistd.h&gt;
    pid_t getpid( void );
</PRE>

<P>
<B>Description:</B> This function returns the task ID of the
calling task. The task ID will be invalid if called at the interrupt
level.
<P>
<B>Input Parameters:</B> None.
<P>
<B>Returned Values:</B> 
<UL>
<LI>The task ID of the calling task.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>POSIX Compatibility:</B>
Compatible with the POSIX interface of the same name.

<H2>2.2 <A NAME="Task_Schedule">Task Scheduling Interfaces</A></H2>

<p>
  By default, NuttX performs strict priority scheduling: Tasks of higher
  priority have exclusive access to the CPU until they become blocked.
  At that time, the CPU is available to tasks of lower priority.
  Tasks of equal priority are scheduled FIFO.
</p>
<p>
  Optionally, a Nuttx task or thread can be configured with round-robin
  scheduler.  This is similar to priority scheduling <i>except</i> that
  tasks with equal priority and share CPU time via <i>time-slicing</i>.
  The time-slice interval is a constant determined by the configuration
  setting <code>CONFIG_RR_INTERVAL</code>.
</p>
<p>
  The OS interfaces described in the following paragraphs provide
  a POSIX- compliant interface to the NuttX scheduler:
</p>
<ul>
  <li><a href="#schedsetparam">2.2.1 sched_setparam</a></li>
  <li><a href="#schedgetparam">2.2.2 sched_getparam</a></li>
  <li><a href="#schedsetscheduler">2.2.3 sched_setscheduler</a></li>
  <li><a href="#setgetscheduler">2.2.4 sched_getscheduler</a></li>
  <li><a href="#sched_yield">2.2.5 sched_yield</a></li>
  <li><a href="#schedgetprioritymax">2.2.6 sched_get_priority_max</a></li>
  <li><a href="#schedgetprioritymin">2.2.7 sched_get_priority_min</a></li>
  <li><a href="#schedgetrrinterval">2.2.8 sched_get_rr_interval</a></li>
</ul>

<H3><a name="schedsetparam">2.2.1 sched_setparam</a></H3>
<p>
  <b>Function Prototype:</b>
<pre>
    #include &lt;sched.h&gt;
    int sched_setparam(pid_t pid, const struct sched_param *param);
</pre>
<p>
  <b>Description:</B>
  This function sets the priority of the task specified by pid input parameter.
</p>
<p>
  NOTE: Setting a task's priority to the same value has the similar
  effect to <code>sched_yield()</code>: The task will be moved to after all
  other tasks with the same priority.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li>
    <code>pid</code>.
    The task ID of the task.
    If <code>pid</code> is zero, the priority of the calling task is set.
  </li>
  <li>
    <code>param</code>.
    A structure whose member <code>sched_priority</code> is the integer priority.
    The range of valid priority numbers is from <code>SCHED_PRIORITY_MIN</code> through <code>SCHED_PRIORITY_MAX</code>.
  </li>
</ul>
<p>
  <b>Returned Values:</b>
  On success, sched_setparam() returns 0 (OK).
  On error, -1 (ERROR) is returned, and errno is set appropriately.
</p>
<ul>

  <li>
    <code>EINVAL</code>.
     The parameter <code>param</code> is invalid or does not make sense for the current scheduling policy.
  </li>
  <li>
    <code>EPERM</code>.
    The calling task does not have appropriate privileges.
  </li>
  <li>
    <code>ESRCH</code>.
    The task whose ID is <code>pid</code> could not be found.
  </li>
</ul>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <B>POSIX  Compatibility:</B>
  Comparable to the POSIX interface of the same name.
  Differences from the full POSIX implementation include:
</p>
<ul>
  <li>The range of priority values for the POSIX call is 0 to 255.</li>
</ul>

<H3><a name="schedgetparam">2.2.2 sched_getparam</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    int sched_getparam (pid_t pid, struct sched_param *param);
</PRE>

<P>
<B>Description:</B> This function gets the scheduling priority
of the task specified by pid.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>pid</I>. The task ID of the task. If pid is zero, the
priority of the calling task is returned.
<li><code>param<code>.</li> A structure whose member sched_priority is the
integer priority. The task's priority is copied to the sched_priority
element of this structure.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) if successful, otherwise -1 (ERROR).
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="schedsetscheduler">2.2.3 sched_setscheduler</a></H3>
<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    int sched_setscheduler (pid_t pid, int policy, const struct sched_param *param);
</PRE>
<P>
  <B>Description:</B>
  <i>sched_setscheduler()</i>  sets both the scheduling policy
  and the priority for the task identified by pid.
  If pid equals zero, the scheduler of the calling
  thread will be set.
  The parameter 'param' holds the priority of the thread under the new policy.
</p>
<P>
<B>Input Parameters:</B> 
<UL>
  <LI><I>pid</I>. The task ID of the task. If pid is zero, the
    priority of the calling task is set.
  <LI><I>policy</I>. Scheduling policy requested (either SCHED_FIFO
    or SCHED_RR).
  <li><code>param<code>.</li> A structure whose member sched_priority is the
    integer priority. The range of valid priority numbers is from
    SCHED_PRIORITY_MIN through SCHED_PRIORITY_MAX.
</UL>
<P>
  <B>Returned Values:</B> 
  On success, <i>sched_setscheduler()</i> returns OK (zero).  On
  error, ERROR (-1) is returned, and errno is set appropriately:
</p>
<ul>
  <li>EINVAL The scheduling policy is not one of the
    recognized policies.</li>
  <li>ESRCH  The task whose ID is pid could not be found.</li>
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="setgetscheduler">2.2.4 sched_getscheduler</a></H3>
<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    int sched_getscheduler (pid_t pid);
</PRE>
<P>
  <B>Description:</B>
  <i>sched_getscheduler()</i> returns the scheduling policy
  currently applied to the task identified by pid. If
  pid equals zero, the policy of the calling process will
  be retrieved.
 *
 * Inputs:
 *
 * Return Value:

 This function returns the current scheduling
policy.
<P>
<B>Input Parameters:</B> 
<UL>
  <LI><I>pid</I>.
    The task ID of the task to query.
    If pid is zero, the calling task is queried.
  </LI>
</UL>
<P>
<B>Returned Values:</B> 
<UL>
  <LI>
    On success, <i>sched_getscheduler()</i> returns the policy for
    the task (either SCHED_FIFO or SCHED_RR).
    On error,  ERROR (-1) is returned, and errno is set appropriately:
    <ul>
      <li>ESRCH  The task whose ID is pid could not be found.</li>
    </ul>
  </li>
</UL>
<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<UL>
<LI>Does not report errors via <I>errno</I>.
</UL>

<H3><a name="sched_yield">2.2.5 sched_yield</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    int sched_yield( void );
</PRE>

<P>
<B>Description:</B> This function forces the calling task to give
up the CPU (only to other tasks at the same priority).
<P>
<B>Input Parameters:</B> None.
<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) or -1 (ERROR)
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="schedgetprioritymax">2.2.6 sched_get_priority_max</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    int sched_get_priority_max (int policy)
</PRE>

<P>
<B>Description:</B> This function returns the value of the highest
possible task priority for a specified scheduling policy.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>policy</I>. Scheduling policy requested.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>The maximum priority value or -1 (ERROR).
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="schedgetprioritymin">2.2.7 sched_get_priority_min</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    int sched_get_priority_min (int policy);
</PRE>

<P>
<B>Description:</B> This function returns the value of the lowest
possible task priority for a specified scheduling policy.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>policy</I>. Scheduling policy requested.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>The minimum priority value or -1 (ERROR)
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="schedgetrrinterval">2.2.8 sched_get_rr_interval</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    int sched_get_rr_interval (pid_t pid, struct timespec *interval);
</PRE>

<P>
  <B>Description:</B> 
  <i>sched_rr_get_interval()</i>  writes  the timeslice interval
  for task identified by <i>pid</i> into  the timespec structure
  pointed to by <i>interval</i>.  If pid is zero, the timeslice
  for the calling process is written into 'interval.  The
  identified process should be running under the SCHED_RR
  scheduling policy.'
</p>
<P>
  <B>Input Parameters:</B> 
</p>
<UL>
<LI><I>pid</I>. The task ID of the task. If pid is zero, the
priority of the calling task is returned.
<LI><I>interval</I>. A structure used to return the time slice.
</UL>

<P>
  <B>Returned Values:</B> 
  On success, sched_rr_get_interval() returns OK (0).  On
  error, ERROR (-1) is returned, and errno is set to:
</p>
<UL>
  <LI>EFAULT Cannot copy to interval</LI>
  <LI>EINVAL Invalid pid.</LI>
  <LI>ENOSYS The system call is not yet implemented.</LI>
  <LI>ESRCH  The process whose ID is pid could not be found.</LI>
</UL>

<P>
  <B>Assumptions/Limitations:</B> 
<P>
  <B>POSIX  Compatibility:</B> Comparable to the POSIX
  interface of the same name.
</P>

<H2>2.3 <A NAME="Task_Switch">Task Switching Interfaces</A></H2>

<ul>
  <li><a href="#schedlock">2.3.1 sched_lock</a></li>
  <li><a href="#schedunlock">2.3.2 sched_unlock</a></li>
  <li><a href="#schedlockcount">2.3.3 sched_lockcount</a></li>
</ul>

<H3><a name="schedlock">2.3.1 sched_lock</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    STATUS sched_lock( void );
</PRE>

<P>
<B>Description:</B> This function disables context switching by
Disabling addition of new tasks to the ready-to-run task list.
The task that calls this function will be the only task that is
allowed to run until it either calls sched_unlock (the appropriate
number of times) or until it blocks itself.
<P>
<B>Input Parameters:</B> None.
<P>
<B>Returned Values:</B> 
<UL>
<LI>OK or ERROR.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the comparable interface:
<PRE>
    STATUS taskLock( void );
</PRE>

<H3><a name="schedunlock">2.3.2 sched_unlock</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    STATUS sched_unlock( void );
</PRE>

<P>
<B>Description:</B> This function decrements the preemption lock
count. Typically this is paired with sched_lock() and concludes
a critical section of code. Preemption will not be unlocked until
sched_unlock() has been called as many times as sched_lock().
When the lockCount is decremented to zero, any tasks that were
eligible to preempt the current task will execute.
<P>
<B>Input Parameters:</B> None.
<P>
<B>Returned Values:</B> 
<UL>
<LI>OK or ERROR.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the comparable interface:
<PRE>
    STATUS taskUnlock( void );
</PRE>

<H3><a name="schedlockcount">2.3.3 sched_lockcount</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;sched.h&gt;
    sint32 sched_lockcount( void )
</PRE>

<P>
<B>Description:</B> This function returns the current value of
the lockCount. If zero, preemption is enabled; if non-zero, this
value indicates the number of times that sched_lock() has been called
on this thread of execution.
<P>
<B>Input Parameters:</B> None.
<P>
<B>Returned Values:</B> 
<UL>
<LI>The current value of the lockCount.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> None.
<HR>

<H2>2.4 <A NAME="Message_Queue">Named Message Queue Interfaces</A></H2>

<p>
  NuttX supports POSIX named message queues for intertask communication.
  Any task may send or receive messages on named message queues.
  Interrupt handlers may send messages via named message queues.
</p>
<ul>
  <li><a href="#mqopen">2.4.1 mq_open</a></li>
  <li><a href="#mqclose">2.4.2 mq_close</a></li>
  <li><a href="#mqunlink">2.4.3 mq_unlink</a></li>
  <li><a href="#mqsend">2.4.4 mq_send</a></li>
  <li><a href="#mqreceive">2.4.5 mq_receive</a></li>
  <li><a href="#mqnotify">2.4.6 mq_notify</a></li>
  <li><a href="#mqsetattr">2.4.7 mq_setattr</a></li>
  <li><a href="#mqgetattr">2.4.8 mq_getattr</a></li>
</ul>

<H3><a name="mqopen">2.4.1 mq_open</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;mqueue.h&gt;
    mqd_t mq_open( const char *mqName, int oflags, ... );
</PRE>

<P>
<B>Description:</B> This function establish a connection between
a named message queue and the calling task. After a successful
call of mq_open(), the task can reference the message queue using
the address returned by the call. The message queue remains usable
until it is closed by a successful call to mq_close().
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>mqName</I>. Name of the queue to open
<LI><I>oflags</I>. Open flags. These may be any combination of:
<UL>
<LI><I>O_RDONLY</I>. Open for read access.
<LI><I>O_WRONLY</I>. Open for write access.
<LI><I>O_RDWR</I>. Open for both read &amp; write access.
<LI><I>O_CREAT</I>. Create message queue if it does not already
exist.
<LI><I>O_EXCL</I>. Name must not exist when opened.
<LI><I>O_NONBLOCK</I>. Don't wait for data.
</UL>

<LI><I>... Optional parameters</I>.
When the O_CREAT flag is specified, POSIX requires that a third
and fourth parameter be supplied:
<UL>
<LI><I>mode</I>.  The mode parameter is of type mode_t.  In the POSIX
specification, this mode value provides file permission bits for the
message queue.  This parameter is required but not used in the present
implementation.
<LI><I>attr</I>.  A pointer to an mq_attr that is provided to initialize.
the message queue.  If attr is NULL, then the messages queue is created
with implementation-defined default message queue attributes.  If attr is
non-NULL, then the message queue mq_maxmsg attribute is set to the
corresponding value when the queue is created.  The mq_maxmsg attribute
determines the maximum number of messages that can be queued before
addition attempts to send messages on the message queue fail or cause the
sender to block; the mq_msgsize attribute determines the maximum size of a
message that can be sent or received.  Other elements of attr are ignored
(i.e, set to default message queue attributes).
</UL>
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>A message queue descriptor or -1 (ERROR)
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX interface
of the same name.
Differences from the full POSIX implementation include:
<UL>
<LI>The mq_msgsize attributes determines the maximum size of a message that
may be sent or received.  In the present implementation, this maximum
message size is limited at 22 bytes.
</UL>

<H3><a name="mqclose">2.4.2 mq_close</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;mqueue.h&gt;
    int mq_close( mqd_t mqdes );
</PRE>

<P>
<B>Description:</B> This function is used to indicate that the
calling task is finished with the specified message queued mqdes.
The mq_close() deallocates any system resources allocated by the
system for use by this task for its message queue.
<P>
If the calling task has attached a notification request to the message
queue via this <I>mqdes</I> (see mq_notify()), this attachment will be
removed and the message queue is available for another task to attach
for notification.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>mqdes</I>. Message queue descriptor.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) if the message queue is closed successfully, otherwise,
-1 (ERROR).
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<UL>
<LI>The behavior of a task that is blocked on either a mq_send() or
mq_receive() is undefined when mq_close() is called.
<LI>The result of using this message queue descriptor after successful
return from mq_close() is undefined.
</UL>
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX interface
of the same name.

<H3><a name="mqunlink">2.4.3 mq_unlink</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;mqueue.h&gt;
    int mq_unlink( const char *mqName );
</PRE>

<P>
<B>Description:</B> This function removes the message queue named
by &quot;mqName.&quot; If one or more tasks have the message queue
open when mq_unlink() is called, removal of the message queue
is postponed until all references to the message queue have been
closed.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>mqName</I>. Name of the message queue
</UL>

<P>
<B>Returned Values:</B> None.
<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="mqsend">2.4.4 mq_send</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;mqueue.h&gt;
    int mq_send( mqd_t mqdes, const void *msg, size_t msgLen, int msgPrio );
</PRE>

<P>
<B>Description:</B> This function adds the specified message (msg)
to the message queue (mqdes). The &quot;msgLen&quot; parameter
specifies the length of the message in bytes pointed to by &quot;msg.&quot;
This length must not exceed the maximum message length from the
mq_getattr().
<P>
If the message queue is not full, mq_send() will in the message
in the message queue at the position indicated by the &quot;msgPrio&quot;
argument. Messages with higher priority will be inserted before
lower priority messages. The value of &quot;msgPrio&quot; must
not exceed MQ_PRIO_MAX.
<P>
If the specified message queue is full and O_NONBLOCK is not
set in the message queue, then mq_send() will block until space
becomes available to the queue the message.
<P>
If the message queue is full and osNON_BLOCK is set, the message
is not queued and ERROR is returned.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>mqdes</I>. Message queue descriptor
<LI><I>msg</I>. Message to send
<LI><I>msgLen</I>. The length of the message in bytes
<LI><I>msgPrio</I>. The priority of the message
</UL>

<P>
<B>Returned Values:</B> None.
<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<UL>
<LI>Control is not returned if a signal is received.
</UL>

<H3><a name="mqreceive">2.4.5 mq_receive</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;mqueue.h&gt;
    int mq_receive( mqd_t mqdes, void *msg, size_t msgLen, int *msgPrio );
</PRE>

<P>
<B>Description:</B> This function receives the oldest of the highest
priority messages from the message queue specified by &quot;mqdes.&quot;
If the size of the buffer in bytes (msgLen) is less than the &quot;mq_msgsize&quot;
attribute of the message queue, mq_receive will return an error.
Otherwise, the select message is removed from the queue and copied
to &quot;msg.&quot;
<P>
If the message queue is empty and O_NONBLOCK was not set, mq_receive()
will block until a message is added to the message queue. If more
than one task is waiting to receive a message, only the task with
the highest priority that has waited the longest will be unblocked.
<P>
If the queue is empty and O_NONBLOCK is set, ERROR will be
returned.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>mqdes</I>. Message Queue Descriptor
<LI><I>msg</I>. Buffer to receive the message
<LI><I>msgLen</I>. Size of the buffer in bytes
<LI><I>msgPrio</I>. If not NULL, the location to store message
priority.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>Length of the selected message in bytes, otherwise -1 (ERROR).
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<UL>
<LI>Control is not returned if a signal is received.
</UL>

<H3><a name="mqnotify">2.4.6 mq_notify</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;mqueue.h&gt;
    int mq_notify( mqd_t mqdes, const struct sigevent *notification );
</PRE>

<P>
<B>Description:</B> If the &quot;notification&quot; input parameter
is not NULL, this function connects the task with the message queue such
that the specified signal will be sent to the task whenever the message
changes from empty to non-empty. One notification can be attached
to a message queue.
<P>
If &quot;notification&quot; is NULL, the attached notification
is detached (if it was held by the calling task) and the queue
is available to attach another notification.
<P>
When the notification is sent to the registered task, its registration
will be removed.  The message queue will then be available for
registration.
<P>
<B>Input Parameters:</B>
<UL>
<LI><I>mqdes</I>. Message queue descriptor
<LI><I>notification</I>. Real-time signal structure containing:
<UL>
<LI><I>sigev_notify</I>. Should be osSIGEV_SIGNAL (but actually
ignored)
<LI><I>sigev_signo</I>. The signo to use for the notification
<LI><I>sigev_value</I>. Value associated with the signal
</UL>

</UL>

<P>
<B>Returned Values:</B> None.
<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX interface
of the same name.
Differences from the full POSIX implementation include:
<UL>
<LI>The notification signal will be sent to the registered task even if
another task is waiting for the message queue to become non-empty.  This is
inconsistent with the POSIX specification which states, &quot;If a process
has registered for notification of message arrival at a message queue and
some process is blocked in <I>mq_receive</I> waiting to receive a message
when a message arrives at the queue, the arriving message shall satisfy the
appropriate <I>mq_receive()</I> ... The resulting behavior is as if the
message queue remains empty, and no notification shall be sent.&quot;
</UL>

<H3><a name="mqsetattr">2.4.7 mq_setattr</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;mqueue.h&gt;
    int mq_setattr( mqd_t mqdes, const struct mq_attr *mqStat,
                     struct mq_attr *oldMqStat);
</PRE>

<P>
<B>Description:</B> This function sets the attributes associated
with the specified message queue &quot;mqdes.&quot; Only the &quot;O_NONBLOCK&quot;
bit of the &quot;mq_flags&quot; can be changed.
<P>
If &quot;oldMqStat&quot; is non-null, mq_setattr() will store
the previous message queue attributes at that location (just as
would have been returned by mq_getattr()).
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>mqdes</I>. Message queue descriptor
<LI><I>mqStat</I>. New attributes
<LI><I>oldMqState</I>. Old attributes
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) if attributes are set successfully, otherwise -1
(ERROR).
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="mqgetattr">2.4.8 mq_getattr</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;mqueue.h&gt;
    int mq_getattr( mqd_t mqdes, struct mq_attr *mqStat);
</PRE>

<P>
<B>Description:</B> This functions gets status information and
attributes associated with the specified message queue.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>mqdes</I>. Message queue descriptor
<LI><I>mqStat</I>. Buffer in which to return attributes. The returned
attributes include:
<UL>
<LI><I>mq_maxmsg</I>. Max number of messages in queue.
<LI><I>mq_msgsize</I>. Max message size.
<LI><I>mq_flags</I>. Queue flags.
<LI><I>mq_curmsgs</I>. Number of messages currently in queue.
</UL>

</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) if attributes provided, -1 (ERROR) otherwise.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H2>2.5 <A NAME="Semaphores">Counting Semaphore Interfaces</A></H2>

<p>
  <b>Semaphores</b>.  Semaphores are the basis for
  synchronization and mutual exclusion in NuttX. NuttX supports
  POSIX semaphores.
</p>
<p>
  Semaphores are the preferred mechanism for gaining exclusive access to a
  resource.  sched_lock() and sched_unlock() can also be used for this purpose.
  However, sched_lock() and sched_unlock() have other undesirable side-affects
  in the operation of the system:  sched_lock() also prevents higher-priority
  tasks from running that do not depend upon the semaphore-managed resource
  and, as a result, can adversely affect system response times.
</p>
<p>
  <B>Priority Inversion</B>.  Proper use of semaphores avoids the issues of
  sched_lock().  However, consider the following example:
  <OL>
    <LI>Some low-priority task, <I>Task C</I>, acquires a semphore in order to
      get exclusive access to a protected resource.</li>
    <LI><I>Task C</I> is suspended to allow some high-priority task,</li>
      <I>Task A</I>, to execute.</li>
    <LI><I>Task A</I> attempts to acquire the semaphore held by <I>Task C</I> and
      gets blocked until <I>Task C</I> relinquishes the semaphore.</li>
    <LI><I>Task C</I> is allowed to execute again, but gets suspended by some
      medium-priority <I>Task B</I>.</li>
  </OL>
<p>
  At this point, the high-priority <I>Task A</I> cannot execute until
  <I>Task B</I> (and possibly other medium-priority tasks) completes and until
  <I>Task C</I> relinquishes the semaphore.  In effect, the high-priority task,
  <I>Task A</I> behaves as though it were lower in priority than the
  low-priority task, <I>Task C</I>!  This phenomenon is called <I>priority
  inversion</I>.
</p>
<p>
  Some operating systems avoid priority inversion by <I>automatically</I>
  increasing the priority of the low-priority <I>Task C</I> (the operable
  buzz-word for this behavior is <I>priority inheritance</I>).  NuttX does not
  support this behavior.  As a consequence, it is left to the designer to
  provide implementations that will not suffer from priority inversion.
  The designer may, as examples:
</p>
<UL>
  <LI>Implement all tasks that need the semphore-managed resources at the
    same priority level,</li>
  <LI>Boost the priority of the low-priority task before the semaphore is
    acquired, or</li>
  <LI>Use sched_lock() in the low-priority task.</li>
</UL>
<p>
  POSIX semaphore interfaces:
</p>
<ul>
  <li><a href="#seminit">2.5.1 sem_init</a></li>
  <li><a href="#semdestroy">2.5.2 sem_destroy</a></li>
  <li><a href="#semopen">2.5.3 sem_open</a></li>
  <li><a href="#semclose">2.5.4 sem_close</a></li>
  <li><a href="#semunlink">2.5.5 sem_unlink</a></li>
  <li><a href="#semwait">2.5.6 sem_wait</a></li>
  <li><a href="#semtrywait">2.5.7 sem_trywait</a></li>
  <li><a href="#sempost">2.5.8 sem_post</a></li>
  <li><a href="#semgetvalue">2.5.9 sem_getvalue</a></li>
</ul>

<H3><a name="seminit">2.5.1 sem_init</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    int sem_init ( sem_t *sem, int pshared, unsigned int value );
</PRE>

<P>
<B>Description:</B> This function initializes the UN-NAMED semaphore
sem. Following a successful call to sem_init(), the semaphore
may be used in subsequent calls to sem_wait(), sem_post(), and
sem_trywait(). The semaphore remains usable until it is destroyed.
<P>
Only <I>sem</I> itself may be used for performing synchronization.  The
result of referring to copies of <I>sem</I> in calls to <I>sem_wait()</I>,
<I>sem_trywait()</I>, <I>sem_post()</I>, and <I>sem_destroy()</I>, is
not defined.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>sem</I>. Semaphore to be initialized
<LI><I>pshared</I>. Process sharing (not used)
<LI><I>value</I>. Semaphore initialization value 
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if unsuccessful.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<UL>
<LI>pshared is not used.
</UL>

<H3><a name="semdestroy">2.5.2 sem_destroy</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    int sem_destroy ( sem_t *sem );
</PRE>

<P>
<B>Description:</B> This function is used to destroy the un-named semaphore
indicated by <I>sem</I>.  Only a semaphore that was created using
<I>sem_init()</I> may be destroyed using <I>sem_destroy()</I>.  The effect
of calling <I>sem_destroy()</I> with a named semaphore is undefined.  The
effect of subsequent use of the semaphore <I>sem</I> is undefined until
<I>sem</I> is re-initialized by another call to <I>sem_init()</I>.
<P>
The effect of destroying a semaphore upon which other tasks are currently
blocked is undefined.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>sem</I>. Semaphore to be destroyed.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if unsuccessful.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="semopen">2.5.3 sem_open</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    sem_t *sem_open ( const char *name, int oflag, ...);
</PRE>

<P>
<B>Description:</B> This function establishes a connection between
named semaphores and a task. Following a call to sem_open() with
the semaphore name, the task may reference the semaphore associated
with name using the address returned by this call. The semaphore
may be used in subsequent calls to sem_wait(), sem_trywait(),
and sem_post(). The semaphore remains usable until the semaphore
is closed by a successful call to sem_close().
<P>
If a task makes multiple calls to sem_open() with the same name,
then the same semaphore address is returned (provided there have
been no calls to sem_unlink()).
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>name</I>. Semaphore name
<LI><I>oflag</I>. Semaphore creation options. This may one of
the following bit settings:
<UL>
<LI><I>oflag</I> = 0: Connect to the semaphore only if it already
exists.
<LI><I>oflag</I> = O_CREAT: Connect to the semaphore if it exists,
otherwise create the semaphore.
<LI><I>oflag</I> = O_CREAT with O_EXCL (O_CREAT|O_EXCL): Create
a new semaphore unless one of this name already exists.
</UL>
<LI>... Optional parameters.
NOTE:  When the O_CREAT flag is specified, POSIX requires that a third
and fourth parameter be supplied:
<UL>
<LI><I>mode</I>.  The mode parameter is of type mode_t.  
This parameter is required but not used in the present
implementation.
<LI><I>value</I>.  The value parameter is type unsigned int.  The semaphore
is created with an initial value of <I>value</I>.  Valid initial values for
semaphores must be less than or equal to <I>SEM_VALUE_MAX</I> (defined in
<CODE>include/limits.h</CODE>).
</UL>
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>A pointer to sem_t or -1 (ERROR) if unsuccessful.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<UL>
<LI>Treatment of links/connections is highly simplified. It is
just a counting semaphore.
</UL>

<H3><a name="semclose">2.5.4 sem_close</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    int sem_close ( sem_t *sem );
</PRE>

<P>
<B>Description:</B> This function is called to indicate that the
calling task is finished with the specified named semaphore, sem.
The sem_close() deallocates any system resources allocated by
the system for this named semaphore.
<P>
If the semaphore has not been removed with a call to sem_unlink(),
then sem_close() has no effect on the named semaphore. However,
when the named semaphore has been fully unlinked, the semaphore
will vanish when the last task closes it.
<P>
Care must be taken to avoid risking the deletion of a semaphore
that another calling task has already locked.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>sem</I>. Semaphore descriptor
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if unsuccessful.
</UL>

<P>
<B>Assumptions/Limitations:</B>
<UL>
<LI>Care must be taken to avoid deletion of a semaphore that another task
has already locked.
<LI>sem_close() must not be called with an un-named semaphore.
</UL>
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="semunlink">2.5.5 sem_unlink</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    int sem_unlink ( const char *name );
</PRE>

<P>
<B>Description:</B> This function will remove the semaphore named by the
input name parameter.  If one or more tasks have the semaphore named by
name oepn when sem_unlink() is called, destruction of the semaphore will
be postponed until all references have been destroyed by calls to
sem_close().
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>name</I>. Semaphore name
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if unsuccessful.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<UL>
<LI>Care must be taken to avoid deletion of a semaphore that another task
has already locked.
<LI>sem_unlink() must not be called with an un-named semaphore.
</UL>
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the full POSIX implementation include:
<UL>
<LI>Treatment of links/connections is highly simplified. It is
just a counting semaphore.
<LI>Calls to sem_open() to re-create or re-connect to the semaphore may
refer to the same semaphore; POSIX specifies that a new semaphore with the
same name should be created after sem_unlink() is called.
</UL>

<H3><a name="semwait">2.5.6 sem_wait</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    int sem_wait ( sem_t *sem );
</PRE>

<P>
<B>Description:</B> This function attempts to lock the semaphore
referenced by sem. If the semaphore as already locked by another
task, the calling task will not return until it either successfully acquires
the lock or the call is interrupted by a signal.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>sem</I>. Semaphore descriptor.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) is unsuccessful
</UL>
<P>
If <I>sem_wait</I> returns -1 (ERROR) then the cause of the failure
will be indicated by the thread-specific <I>errno</I> value (a pointer
to this value can be obtained using <I>get_errno_ptr()</I>).  The following
lists the possible values for <I>errno</I>:
<P>
<UL>
<LI><I>EINVAL</I>:  Indicates that the <I>sem</I> input parameter is
not valid.
<LI><I>EINTR</I>:  Indicates that the wait was interrupt by a signal
received by this task.  In this case, the semaphore has not be acquired.
</UL>
<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="semtrywait">2.5.7 sem_trywait</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    int sem_trywait ( sem_t *sem );
</PRE>

<P>
<B>Description:</B> This function locks the specified semaphore
only if the semaphore is currently not locked.  In any event, the call
returns without blocking.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>sem</I>. The semaphore descriptor
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) or -1 (ERROR) if unsuccessful
</UL>
If <I>sem_wait</I> returns -1 (ERROR) then the cause of the failure
will be indicated by the thread-specific <I>errno</I> value (a pointer
to this value can be obtained using <I>get_errno_ptr()</I>).  The following
lists the possible values for <I>errno</I>:
<P>
<UL>
<LI><I>EINVAL</I>:  Indicates that the <I>sem</I> input parameter is
not valid.
<LI><I>EAGAIN</I>:  Indicates that the semaphore was not acquired.
</UL>
<P>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sempost">2.5.8 sem_post</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    int sem_post ( sem_t *sem );
</PRE>

<P>
<B>Description:</B> When a task has finished with a semaphore,
it will call sem_post().  This function unlocks the semaphore referenced
by <I>sem</I> by performing the semaphore unlock operation.
<P>
If the semaphore value resulting from this operation is positive, then
no tasks were blocked waiting for the semaphore to become unlocked;
The semaphore value is simply incremented.
<P>
If the value of the semaphore resulting from this operation is zero, then
on of the tasks blocked waiting for the semaphore will be allowed to
return successfully from its call to <I>sem_wait()</I>.
<P>
<B>NOTE</B>:  <I>sem_post()</I> may be called from an interrupt handler.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>sem</I>. Semaphore descriptor
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) or -1 (ERROR) if unsuccessful.
</UL>

<P>
<B>Assumptions/Limitations:</B> This function cannot be called
from an interrupt handler. It assumes the currently executing
task is the one that is performing the unlock.
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="semgetvalue">2.5.9 sem_getvalue</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;semaphore.h&gt;
    int sem_getvalue ( sem_t *sem, int *sval );
</PRE>

<P>
<B>Description:</B> This function updates the location referenced
by sval argument to have the value of the semaphore referenced
by sem without effecting the state of the semaphore. The updated
value represents the actual semaphore value that occurred at some
unspecified time during the call, but may not reflect the actual
value of the semaphore when it is returned to the calling task.
<P>
If sem is locked, the value return by sem_getvalue() will either
be zero or a negative number whose absolute value represents the
number of tasks waiting for the semaphore.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>sem</I>. Semaphore descriptor
<LI><I>sval</I>. Buffer by which the value is returned
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) or -1 (ERROR) if unsuccessful.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<HR>

<H2>2.6 <A NAME="Watchdogs">Watchdog Timer Interfaces</A></H2>

<P>
  NuttX provides a general watchdog timer facility.
  This facility allows the NuttX user to specify a watchdog timer function
  that will run after a specified delay.
  The watchdog timer function will run in the context of the timer interrupt handler.
  Because of this, a limited number of NuttX interfaces are available to he watchdog timer function.
  However, the watchdog timer function may use mq_send(), sigqueue(), or kill() to communicate with NuttX tasks.
</p>
<ul>
  <li><a href="#wdcreate">2.6.1 wd_create</a></li>
  <li><a href="#wddelete">2.6.2 wd_delete</a></li>
  <li><a href="#wdstart">2.6.3 wd_start</a></li>
  <li><a href="#wdcancel">2.6.4 wd_cancel</a></li>
  <li><a href="#wdgettime">2.6.5 wd_gettime</a></li>
</ul>

<H3><a name="wdcreate">2.6.1 wd_create</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;wdog.h&gt;
    WDOG_ID wd_create (void);
</PRE>

<P>
<B>Description:</B> The wd_create function will create a watchdog
by allocating the appropriate resources for the watchdog.
<P>
<B>Input Parameters:</B> None.
<P>
<B>Returned Values:</B> 
<UL>
<LI>Pointer to watchdog that may be used as a handle in subsequent
NuttX calls (i.e., the watchdog ID), or NULL if insufficient resources
are available to create the watchdogs.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following comparable interface:
<PRE>
    WDOG_ID wdCreate (void);
</PRE>

<P>
Differences from the VxWorks interface include:
<UL>
<LI>The number of available watchdogs is fixed (configured at
initialization time).
</UL>

<H3><a name="wddelete">2.6.2 wd_delete</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;wdog.h&gt;
    STATUS wd_delete (WDOG_ID wdog);
</PRE>

<P>
<B>Description:</B> The wd_delete function will deallocate a
watchdog. The watchdog will be removed from the timer queue if
has been started.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>wdog</I>. The watchdog ID to delete. This is actually a
pointer to a watchdog structure.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>OK or ERROR
</UL>

<P>
<B>Assumptions/Limitations:</B> It is the responsibility of the
caller to assure that the watchdog is inactive before deleting
it.
<P>
<B>  POSIX  Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following comparable interface:
<PRE>
    STATUS wdDelete (WDOG_ID wdog);
</PRE>

<P>
Differences from the VxWorks interface include:
<UL>
<LI>Does not make any checks to see if the watchdog is being used
before de-allocating it (i.e., never returns ERROR).
</UL>

<H3><a name="wdstart">2.6.3 wd_start</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;wdog.h&gt;
    STATUS wd_start( WDOG_ID wdog, int delay, wdentry_t wdentry,
                     intt argc, ....);
</PRE>

<P>
<B>Description:</B> This function adds a watchdog to the timer
queue. The specified watchdog function will be called from the
interrupt level after the specified number of ticks has elapsed.
Watchdog timers may be started from the interrupt level.
<P>
Watchdog times execute in the context of the timer interrupt handler, but
with the PIC/PID address environment that was in place when wd_start()
was called.
<P>
Watchdog timers execute only once.
<P>
To replace either the timeout delay or the function to be executed,
call wd_start again with the same wdog; only the most recent
wd_start() on a given watchdog ID has any effect.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>wdog</I>. Watchdog ID
<LI><I>delay</I>. Delay count in clock ticks
<LI><I>wdentry</I>. Function to call on timeout
<LI><I>argc</I>.  The number of uint32 parameters to pass to wdentry.
<LI><I>...</I>. uint32 size parameters to pass to wdentry
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>OK or ERROR
</UL>

<P>
<B>Assumptions/Limitations:</B> The watchdog routine runs in the
context of the timer interrupt handler and is subject to all ISR
restrictions.
<P>
<B>  POSIX  Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following comparable interface:
<PRE>
    STATUS wdStart (WDOG_ID wdog, int delay, FUNCPTR wdentry, int parameter);
</PRE>

<P>
Differences from the VxWorks interface include:
<UL>
<LI>The present implementation supports multiple parameters passed
to wdentry; VxWorks supports only a single parameter.  The maximum
number of parameters is determined by 
</UL>

<H3><a name="wdcancel">2.6.4 wd_cancel</a></H3>
<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;wdog.h&gt;
    STATUS wd_cancel (WDOG_ID wdog);
</PRE>

<P>
<B>Description:</B> This function cancels a currently running
watchdog timer. Watchdog timers may be canceled from the interrupt
level.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>wdog</I>. ID of the watchdog to cancel.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>OK or ERROR
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> This is a NON-POSIX interface.
VxWorks provides the following comparable interface:
<PRE>
    STATUS wdCancel (WDOG_ID wdog);
</PRE>

<h3><a name="wdgettime">2.6.5 wd_gettime</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;wdog.h&gt;
    Sint wd_gettime(WDOG_ID wdog);
</pre>
<p>
  <b>Description:</b> 
   This function returns the time remaining before the the specified watchdog expires.
</p>
<p>
  <b>Input Parameters:</b>
  <ul>
    <li><code>wdog</code>. Identifies the watchdog that the request is for.</li>
  </ul>
</p>
<p>
  <b>Returned Value:</b> 
  The time in system ticks remaining until the watchdog time expires.  Zero
  means either that wdog is not valid or that the wdog has already expired.
</p>

<HR>

<H2><A NAME="ClocksNTimers">2.7 Clocks and Timers</A></H2>
<ul>
  <li><a href="#clocksettime">2.7.1 clock_settime</a></li>
  <li><a href="#clockgettime">2.7.2 clock_gettime</a></li>
  <li><a href="#clockgetres">2.7.3 clock_getres</a></li>
  <li><a href="#mktime">2.7.4 mktime</a></li>
  <li><a href="#gmtimer">2.7.5 gmtime_r</a></li>
  <li><a href="#localtimer">2.7.6 localtime_r</a></li>
  <li><a href="#timercreate">2.7.7 timer_create</a></li>
  <li><a href="#timerdelete">2.7.8 timer_delete</a></li>
  <li><a href="#timersettime">2.7.9 timer_settime</a></li>
  <li><a href="#timergettime">2.7.10 timer_gettime</a></li>
  <li><a href="#timergetoverrun">2.7.11 timer_getoverrun</a></li>
</ul>

<H3><a name="clocksettime">2.7.1 clock_settime</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    int clock_settime(clockid_t clockid, const struct timespec *tp);
</pre>
<p>
  <b>Description:</b>
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>parm</code>. </li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <I>clock_settime()</I> function will return zero (<I>OK</I>).
  Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
  <li><code>Exxx</code>.</li>
</ul>

<H3><a name="clockgettime">2.7.2 clock_gettime</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    int clock_gettime(clockid_t clockid, struct timespec *tp);
</pre>
<p>
  <b>Description:</b>
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>parm</code>. </li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <I>clock_gettime()</I> function will return zero (<I>OK</I>).
  Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
  <li><code>Exxx</code>.</li>
</ul>

<H3><a name="clockgetres">2.7.3 clock_getres</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    int clock_getres(clockid_t clockid, struct timespec *res);
</pre>
<p>
  <b>Description:</b>
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>parm</code>. </li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <I>clock_getres()</I> function will return zero (<I>OK</I>).
  Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
  <li><code>Exxx</code>.</li>
</ul>

<H3><a name="mktime">2.7.4 mktime</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    time_t mktime(struct tm *tp);
</pre>
<p>
  <b>Description:</b>
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>parm</code>. </li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <I>mktime()</I> function will return zero (<I>OK</I>).
  Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
  <li><code>Exxx</code>.</li>
</ul>

<H3><a name="gmtimer">2.7.5 gmtime_r</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    struct tm *gmtime_r(const time_t *clock, struct tm *result);
</pre>
<p>
  <b>Description:</b>
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>parm</code>. </li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <I>gmtime_r()</I> function will return zero (<I>OK</I>).
  Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
  <li><code>Exxx</code>.</li>
</ul>

<H3><a name="localtimer">2.7.6 localtime_r</A></H3>
<pre>
    #include &lt;time.h&gt;
    #define localtime_r(c,r) gmtime_r(c,r)
</pre>

<H3><a name="timercreate">2.7.7 timer_create</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    int timer_create(clockid_t clockid, struct sigevent *evp, timer_t *timerid);
</pre>
<p>
  <b>Description:</b>
  The  <code>timer_create()</code> function creates per-thread timer using the specified
  clock, <code>clock_id</code>, as the timing base.
  The <code>timer_create()</code> function returns, in
  the location referenced by <code>timerid</code>, a timer ID of type timer_t used to identify
  the timer in timer requests.
  This timer ID is unique until the timer is deleted.
  The particular clock, <code>clock_id<code>, is defined in <code>&lt;time.h&gt;<code>.
  The timer whose ID is returned will be in a disarmed state upon return from
  <code>timer_create()</code>.
</p>
<p>
  The <code>evp</code> argument, if non-NULL, points to a <code>sigevent</code> structure.
  This structure is allocated by the called and defines the asynchronous notification to occur.
  If the <code>evp</code> argument is NULL, the effect is as if the <code>evp</code> argument pointed to
  a <code>sigevent</code> structure with the <code>sigev_notify</code> member having the value <code>SIGEV_SIGNAL</code>,
  the <code>sigev_signo</code> having a default signal number, and the <code>sigev_value</code> member
  having the value of the timer ID.
</p>
<p>
  Each implementation defines a set of clocks that can be used as timing bases
  for per-thread timers. All implementations shall support a <code>clock_id</code> of
  <code>CLOCK_REALTIME</code>.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>clockid</code>. Specifies the clock to use as the timing base.
    Must be <code>CLOCK_REALTIME</code>.</li>
  <li><code>evp</code>. Refers to a user allocated sigevent structure that defines the
    asynchronous notification.  evp may be NULL (see above).</li>
  <li><code>timerid</code>. The pre-thread timer created by the call to timer_create().</li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If the call succeeds, <code>timer_create()</code> will return 0 (<code>OK</code>) and update the
  location referenced by <code>timerid</code> to a <code>timer_t</code>, which can be passed to the
  other per-thread timer calls.  If an error occurs, the function will return
  a value of -1 (<code>ERROR</code>) and set errno to indicate the error.
</p>
<ul>
  <li><code>EAGAIN</code>. The system lacks sufficient signal queuing resources to honor the
    request.</li>
  <li><code>EAGAIN</code>. The calling process has already created all of the timers it is
    allowed by this implementation.</li>
  <li><code>EINVAL</code>. The specified clock ID is not defined.</li>
  <li><code>ENOTSUP</code>. The implementation does not support the creation of a timer attached
    to the CPU-time clock that is specified by clock_id and associated with a
    thread different thread invoking timer_create().</li>
</ul>
<p>
  <b>POSIX Compatibility:</b>
  Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
</p>
<ul>
  <li>Only <code>CLOCK_REALTIME</code> is supported for the <code>clockid</code> argument.</li>
</ul>

<H3><a name="timerdelete">2.7.8 timer_delete</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    int timer_delete(timer_t timerid);
</pre>
<p>
  <b>Description:</b>
  The <code>timer_delete()</code> function deletes the specified timer, <code>timerid</code>, previously
  created by the <code>timer_create()</code> function.
  If the timer is armed when <code>timer_delete()</code> is called, the timer will be automatically disarmed before
  removal.
  The disposition of pending signals for the deleted timer is unspecified.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>timerid</code>.
  The pre-thread timer, previously created by the call to timer_create(), to be deleted.</li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <I>timer_delete()</I> function will return zero (<I>OK</I>).
  Otherwise, the function will return a value of -1 (ERROR) and set errno to indicate the error:
</p>
<ul>
  <li><code>EINVAL</code>. The timer specified timerid is not valid.</li>
</ul>
<p>
  <b>POSIX Compatibility:</b>
  Comparable to the POSIX interface of the same name.
</p>

<H3><a name="timersettime">2.7.9 timer_settime</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    int timer_settime(timer_t timerid, int flags, const struct itimerspec *value,
                      struct itimerspec *ovalue);
</pre>
<p>
  <b>Description:</b>
  The <code>timer_settime()</code> function sets the time until the next expiration of the
  timer specified by <code>timerid</code> from the <code>it_value</code> member of the value argument
  and arm the timer if the <code>it_value</code> member of value is non-zero. If the
  specified timer was already armed when <code>timer_settime()</code> is called, this call
  will reset the time until next expiration to the value specified. If the
  <code>it_value</code> member of value is zero, the timer will be disarmed. The effect
  of disarming or resetting a timer with pending expiration notifications is
  unspecified.
</p>
<p>
  If the flag <code>TIMER_ABSTIME</code> is not set in the argument flags, <code>timer_settime()</code>
  will behave as if the time until next expiration is set to be equal to the
  interval specified by the <code>it_value</code> member of value. That is, the timer will
  expire in <code>it_value</code> nanoseconds from when the call is made. If the flag
  <code>TIMER_ABSTIME</code> is set in the argument flags, <code>timer_settime()</code> will behave as
  if the time until next expiration is set to be equal to the difference between
  the absolute time specified by the <code>it_value</code> member of value and the current
  value of the clock associated with <code>timerid</code>.  That is, the timer will expire
  when the clock reaches the value specified by the <code>it_value</code> member of value.
  If the specified time has already passed, the function will succeed and the
  expiration notification will be made.
</p>
<p>
  The reload value of the timer will be set to the value specified by the
  <code>it_interval</code> member of value.  When a timer is armed with a non-zero
  <code>it_interval</code>, a periodic (or repetitive) timer is specified.
</p>
<p>
  Time values that are between two consecutive non-negative integer multiples
  of the resolution of the specified timer will be rounded up to the larger
  multiple of the resolution. Quantization error will not cause the timer to
  expire earlier than the rounded time value.
</p>
<p>
  If the argument <code>ovalue</code> is not NULL, the t<code>imer_settime()</code> function will store,
  in the location referenced by <code>ovalue</code>, a value representing the previous
  amount of time before the timer would have expired, or zero if the timer was
  disarmed, together with the previous timer reload value. Timers will not
  expire before their scheduled time.
</p>
  <b>NOTE:</b>At present, the <code>ovalue</code> argument is ignored.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
 <li><code>timerid</code>. The pre-thread timer, previously created by the call to timer_create(), to be be set.</li>
 <li><code>flags</code>. Specifie characteristics of the timer (see above)</li>
 <li><code>value</code>. Specifies the timer value to set</li>
 <li><code>ovalue</code>. A location in which to return the time remaining from the previous timer setting (ignored).</li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If the timer_gettime() succeeds, a value of 0 (OK) will be returned.
  If an error occurs, the value -1 (ERROR) will be returned, and errno set to indicate the error.
</p>
<ul>
  <li><code>EINVAL</code>. The timerid argument does not correspond to an ID returned by timer_create() but not yet deleted by timer_delete().</li>
  <li><code>EINVAL</code>. A value structure specified a nanosecond value less than zero or greater than or equal to 1000 million,
    and the it_value member of that structure did not specify zero seconds and nanoseconds.</li>
</ul>
<p>
  <b>POSIX Compatibility:</b>
  Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
</p>
<ul>
  <li>The <code>ovalue</code> argument is ignored.</li>
</ul>

<H3><a name="timergettime">2.7.10 timer_gettime</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    int timer_gettime(timer_t timerid, struct itimerspec *value);
</pre>
<p>
  <b>Description:</b>
  The <code>timer_gettime()</code> function will store the amount of time until the
  specified timer, <code>timerid</code>, expires and the reload value of the timer into the
  space pointed to by the <code>value</code> argument. The <code>it_value</code> member of this structure
  will contain the amount of time before the timer expires, or zero if the timer
  is disarmed. This value is returned as the interval until timer expiration,
  even if the timer was armed with absolute time. The <code>it_interval</code> member of
  <code>value</code> will contain the reload value last set by <code>timer_settime()</code>.
</p>
<p>
   Due to the asynchronous operation of this function, the time reported
   by this function could be significantly more than that actual time
   remaining on the timer at any time.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
 <li><code>timerid</code>. Specifies pre-thread timer, previously created by the call to
 t<code>imer_create()</code>, whose remaining count will be returned.</li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <I>timer_gettime()</I> function will return zero (<I>OK</I>).
  Otherwise, an non-zero error number will be returned to indicate the error:
</p>
<ul>
  <li><code>EINVAL</code>.
  The <code>timerid</code> argument does not correspond to an ID returned by
  <code>timer_create()</code> but not yet deleted by <code>timer_delete()</code>.</li>
</ul>
<p>
  <b>POSIX Compatibility:</b>
  Comparable to the POSIX interface of the same name.
</p>

<H3><a name="timergetoverrun">2.7.11 timer_getoverrun</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;time.h&gt;
    int timer_getoverrun(timer_t timerid);
</pre>
<p>
  <b>Description:</b>
  Only a single signal will be queued to the process for a given timer at any
  point in time.  When a timer for which a signal is still pending expires, no
  signal will be queued, and a timer overrun will occur. When a timer
  expiration signal is delivered to or accepted by a process, if the
  implementation  supports  the  <i>Realtime Signals Extension</i>, the
  <code>timer_getoverrun()</code> function will return the timer expiration overrun count for
  the specified timer. The overrun count returned contains the number of extra
  timer expirations that occurred between the time the signal was generated
  (queued) and when it was delivered or accepted, up to but not including an 
  implementation-defined  maximum of <code>DELAYTIMER_MAX</code>. If the number of such
  extra expirations is greater than or equal to <code>DELAYTIMER_MAX</code>, then the
  overrun count will be set to <code>DELAYTIMER_MAX</code>. The value returned by
  <code>timer_getoverrun()</code> will apply to the most recent expiration signal delivery
  or acceptance for the timer.  If no expiration signal has been delivered
  for the timer, or if the <i>Realtime Signals Extension</i> is not supported, the
  return value of <code>timer_getoverrun()</code> is unspecified.
</p>
<p>
  <b>NOTE:</b>  This interface is not currently implemented in NuttX.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
 <li><code>timerid</code>. Specifies pre-thread timer, previously created by the call to
 <code>timer_create()</code>, whose overrun count will be returned.</li>
</ul>
<p>
  <b>Returned Values:</b>
  If the <code>timer_getoverrun()</code> function succeeds, it will return the timer
  expiration overrun count as explained above. <code>timer_getoverrun()</code> will fail if:
</p>
<ul>
  <li><code>EINVAL</code>.
  The <code>timerid</code> argument does not correspond to an ID returned by
  <code>timer_create()</code> but not yet deleted by <code>timer_delete()</code>.</li>
</ul>
<p>
  <b>POSIX Compatibility:</b>
  Comparable to the POSIX interface of the same name. Differences from the full POSIX implementation include:
</p>
<ul>
  <li>This interface is not currently implemented by NuttX.</li>
</ul>

<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<HR>

<H2>2.8 <A NAME="Signals">Signal Interfaces</A></H2>

<p>
  NuttX provides signal interfaces for tasks. Signals are used to
  alter the flow control of tasks by communicating asynchronous events
  within or between task contexts.
  Any task or interrupt handler can post (or send) a signal to a particular task.
  The task being signaled will execute task-specified signal handler
  function the next time that the task has priority.
  The signal handler is a user-supplied function that is bound to
  a specific signal and performs whatever actions are necessary
  whenever the signal is received.
</p>
<p>
  There are no predefined actions for any signal.
  The default action for all signals (i.e., when no signal handler has
  been supplied by the user) is to ignore the signal.
  In this sense, all NuttX are <i>real time</i> signals.
</p>
<p>
  Tasks may also suspend themselves and wait until a signal is received.
</p>
<p>
  The following signal handling interfaces are provided by NuttX:
</p>
<ul>
  <li><a href="#sigemptyset">2.8.1 sigemptyset</a></li>
  <li><a href="#sigfillset">2.8.2 sigfillset</a></li>
  <li><a href="#sigaddset">2.8.3 sigaddset</a></li>
  <li><a href="#sigdelset">2.8.4 sigdelset</a></li>
  <li><a href="#sigismember">2.8.5 sigismember</a></li>
  <li><a href="#sigaction">2.8.6 sigaction</a></li>
  <li><a href="#sigprocmask">2.8.7 sigprocmask</a></li>
  <li><a href="#sigpending">2.8.8 sigpending</a></li>
  <li><a href="#sigsuspend">2.8.9 sigsuspend</a></li>
  <li><a href="#sigwaitinfo">2.8.10 sigwaitinfo</a></li>
  <li><a href="#sigtimedwait">2.8.11 sigtimedwait</a></li>
  <li><a href="#sigqueue">2.8.12 sigqueue</a></li>
  <li><a href="#kill">2.8.13 kill</a></li>
</ul>

<H3><a name="sigemptyset">2.8.1 sigemptyset</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigemptyset(sigset_t *set);
</PRE>

<P>
<B>Description:</B> This function initializes the signal set specified
by set such that all signals are excluded.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>set</I>. Signal set to initialize.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if the signal set cannot be initialized.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sigfillset">2.8.2 sigfillset</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigfillset(sigset_t *set);
</PRE>

<P>
<B>Description:</B> This function initializes the signal set specified
by set such that all signals are included.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>set</I>. Signal set to initialize
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if the signal set cannot be initialized.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sigaddset">2.8.3 sigaddset</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigaddset(sigset_t *set, int signo);
</PRE>

<P>
<B>Description:</B> This function adds the signal specified by
signo to the signal set specified by set.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>set</I>. Signal set to add signal to
<LI><I>signo</I>. Signal to add
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if the signal number is invalid.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sigdelset">2.8.4 sigdelset</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigdelset(sigset_t *set, int signo);
</PRE>

<P>
<B>Description:</B> This function deletes the signal specified
by signo from the signal set specified by set.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>set</I>. Signal set to delete the signal from
<LI><I>signo</I>. Signal to delete
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if the signal number is invalid.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sigismember">2.8.5 sigismember</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int  sigismember(const sigset_t *set, int signo);
</PRE>

<P>
<B>Description:</B> This function tests whether the signal specified
by signo is a member of the set specified by set.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>set</I>. Signal set to test
<LI><I>signo</I>. Signal to test for
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>1 (TRUE), if the specified signal is a member of the set,
<LI>0 (OK or FALSE), if it is not, or
<LI>-1 (ERROR) if the signal number is invalid.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sigaction">2.8.6 sigaction</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigaction( int signo, const struct sigaction *act,
                   struct sigaction *oact );
</PRE>

<P>
<B>Description:</B> This function allows the calling task to
examine and/or specify the action to be associated with a specific
signal.
<P>
The structure sigaction, used to describe an action to be taken, is defined
to include the following members:
<UL>
<LI><I>sa_u.sa_handler</I>.  A pointer to a signal-catching function.
<LI><I>sa_u.sa_sigaction</I>.  An alternative form for the signal catching
function.
<LI><I>sa_mask</I>.  Additional set of signals to be blocked during
execution of the signal-catching function.
<LI><I>sa_flags</I>:  Special flags to affect behavior of a signal.
</UL>
<P>
If the argument act is not NULL, it points to a structure specifying the
action to be associated with the specified signal.  If the argument oact
is not NULL, the action previously associated with the signal is stored
in the location pointed to by the argument oact.  If the argument act is
NULL, signal handling is unchanged by this function call; thus, the call
can be used to enquire about the current handling of a given signal.
<P>
When a signal is caught by a signal-catching function installed by the
sigaction() function, a new signal mask is calculated and installed for
the duration of the signal-catching function.  This mask is formed by taking
the union of the current signal mask and the value of the sa_mask for the
signal being delivered, and then including the signal being delivered.  If
and when the signal handler returns, the original signal mask is restored.
<P>
Signal catching functions execute in the same address environment as the
task that called sigaction() to install the signal-catching function.
<P>
Once an action is installed for a specific signal, it remains installed
until another action is explicitly requested by another call to
sigaction().
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>sig</I>. Signal of interest
<LI><I>act</I>. Location of new handler
<LI><I>oact</I>. Location to store old handler
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if the signal number is invalid.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the POSIX implementation include:
<UL>
<LI>Special values of sa_handler in the struct sigaction act input
not handled (SIG_DFL, SIG_IGN).
<LI>All sa_flags in struct sigaction of act input are ignored
(all treated like SA_SIGINFO).
</UL>

<H3><a name="sigprocmask">2.8.7 sigprocmask</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigprocmask(int how, const sigset_t *set, sigset_t *oset);
</PRE>

<P>
<B>Description:</B> This function allows the calling task to
examine and/or change its signal mask. If the set is not NULL,
then it points to a set of signals to be used to change the currently
blocked set. The value of how indicates the manner in which the
set is changed.
<P>
If there are any pending unblocked signals after the call to sigprocmask(),
those signals will be delivered before sigprocmask() returns.
<P>
If sigprocmask() fails, the signal mask of the task is not changed.
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>how</I>. How the signal mast will be changed:
<UL>
<LI><I>osSIG_BLOCK</I>. The resulting set is the union of the
current set and the signal set pointed to by the <I>set</I> input parameter.
<LI><I>osSIG_UNBLOCK</I>. The resulting set is the intersection
of the current set and the complement of the signal set pointed
to by the <I>set</I> input parameter.
<LI><I>osSIG_SETMASK</I>. The resulting set is the signal set
pointed to by the <I>set</I> input parameter.
</UL>

<LI><I>set</I>. Location of the new signal mask
<LI><I>oset</I>. Location to store the old signal mask
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK), or -1 (ERROR) if how is invalid.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sigpending">2.8.8 sigpending</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigpending( sigset_t *set );
</PRE>

<P>
<B>Description:</B> This function stores the returns the set of
signals that are blocked for delivery and that are pending for
the calling task in the space pointed to by set.
<P>
If the task receiving a signal has the signal blocked via its
sigprocmask, the signal will pend until it is unmasked.  Only one pending
signal (for a given signo) is retained by the system.  This is consistent
with POSIX which states:  &quot;If a subsequent occurrence of a pending
signal is generated, it is implementation defined as to whether the signal
is delivered more than once.&quot;
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>set</I>. The location to return the pending signal set.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>0 (OK) or -1 (ERROR)
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sigsuspend">2.8.9 sigsuspend</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigsuspend( const sigset_t *set );
</PRE>

<P>
<B>Description:</B> The sigsuspend() function replaces the signal mask
with the set of signals pointed to by the argument set and then suspends
the task until delivery of a signal to the task.
<P>
If the effect of the set argument is to unblock a pending signal, then
no wait is performed.
<P>
The original signal mask is restored when sigsuspend() returns.
<P>
Waiting for an empty signal set stops a task without freeing any
resources (a very bad idea).
<P>
<B>Input Parameters:</B>
<UL>
<LI><I>set</I>.  The value of the signal <B>mask</B> to use while
suspended.
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>-1 (ERROR) always
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the POSIX specification include:
<UL>
<LI>POSIX does not indicate that the original signal mask is restored.
<LI>POSIX states that sigsuspend() &quot;suspends the task until
delivery of a signal whose action is either to execute a signal-catching
function or to terminate the task.&quot;  Only delivery of the signal
is required in the present implementation (even if the signal is ignored).
</UL>

<H3><a name="sigwaitinfo">2.8.10 sigwaitinfo</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigwaitinfo(const sigset_t *set, struct siginfo *info);
</PRE>

<P>
<B>Description:</B> This function is equivalent to sigtimedwait()
with a NULL timeout parameter. (see below).
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>set</I>.  The set of pending signals to wait for.
<LI><I>info</I>. The returned signal values
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>Signal number that cause the wait to be terminated, otherwise
-1 (ERROR) is returned.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="sigtimedwait">2.8.11 sigtimedwait</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigtimedwait( const sigset_t *set, struct siginfo *info,
                      const struct timespec *timeout );
</PRE>

<P>
<B>Description:</B> This function selects the pending signal set
specified by the argument set. If multiple signals are pending in set,
it will remove and return the lowest numbered one. If no signals in set
are pending at the time of the call, the calling task will be suspended
until one of the signals in set becomes pending OR until the task
interrupted by an unblocked signal OR until the time interval specified by
timeout (if any), has expired. If timeout is NULL, then the timeout interval
is forever.
<P>
If the info argument is non-NULL, the selected signal number is
stored in the si_signo member and the cause of the signal is store
in the si_code member. The content of si_value is only meaningful
if the signal was generated by sigqueue(). The following values
for si_code are defined in signal.h:
<UL>
  <LI><I>SI_USER</I>. Signal sent from kill, raise, or abort
  <LI><I>SI_QUEUE</I>. Signal sent from sigqueue
  <LI><I>SI_TIMER</I>. Signal is result of timer expiration
  <LI><I>SI_ASYNCIO</I>. Signal is the result of asynch IO completion 
  <LI><I>SI_MESGQ</I>. Signal generated by arrival of a message on an empty message queue.
</UL>

<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>set</I>.  The set of pending signals to wait for.
<LI><I>info</I>. The returned signal values
<LI><I>timeout</I>. The amount of time to wait
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>Signal number that cause the wait to be terminated, otherwise
-1 (ERROR) is returned.
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the POSIX interface include:
<UL>
<LI>Values for si_codes differ
<LI>No mechanism to return cause of ERROR. (It can be inferred
from si_code in a non-standard way).
<LI>POSIX states that &quot;If no signal is pending at the time of the
call, the calling task shall be suspended until one or more signals
in set become pending or until it is interrupted by an unblocked,
<I>caught</I> signal.&quot;  The present implementation does not require
that the unblocked signal be caught; the task will be resumed even if
the unblocked signal is ignored.
</UL>

<H3><a name="sigqueue">2.8.12 sigqueue</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
    #include &lt;signal.h&gt;
    int sigqueue (int tid, int signo, const union sigval value);
</PRE>

<P>
<B>Description:</B> This function sends the signal specified by
signo with the signal parameter value to the task specified
by tid.
<P>
If the receiving task has the signal blocked via its sigprocmask,
the signal will pend until it is unmasked.  Only one pending signal
(for a given signo) is retained by the system.  This is consistent with
POSIX which states:  &quot;If a subsequent occurrence of a pending signal
is generated, it is implementation defined as to whether the signal
is delivered more than once.&quot;
<P>
<B>Input Parameters:</B> 
<UL>
<LI><I>tid</I>. ID of the task to receive signal
<LI><I>signo</I>. Signal number
<LI><I>value</I>. Value to pass to task with signal
</UL>

<P>
<B>Returned Values:</B> 
<UL>
<LI>
  On  success (at least one signal was sent), zero (OK) is returned.
  On error, -1 (ERROR) is returned, and errno is set appropriately.
  <ul>
    <li><code>EGAIN</code>. The limit of signals which may be queued has been reached.</li>
    <li><code>EINVAL</code>. signo was invalid.</li>
    <li><code>EPERM</code>.  The task does not have permission to send the signal to the receiving process.</li>
    <li><code>ESRCH</code>. No process has a PID matching pid.</li>
  </ul>
</UL>

<P>
<B>Assumptions/Limitations:</B> 
<P>
<B>  POSIX  Compatibility:</B> Comparable to the POSIX
interface of the same name.
Differences from the POSIX interface include:
<UL>
<LI>Default action is to ignore signals.
<LI>Signals are processed one at a time in order
<LI>POSIX states that, &quot;If signo is zero (the null signal), error
checking will be performed but no signal is actually sent.&quot;
There is no null signal in the present implementation; a zero signal will
be sent.
</UL>

<H3><a name="kill">2.8.13 kill</a></H3>

<P>
<B>Function Prototype:</B> 
<PRE>
   #include &lt;sys/types.h&gt;
   #include &ltsignal.h&gt;
   int kill(pid_t pid, int sig);
</PRE>

<P>
<B>Description:</B> 
  The kill() system call can be used to send any signal to
  any task.
</p>
<p>
  If the receiving task has the signal blocked via its sigprocmask,
  the signal will pend until it is unmasked.  Only one pending signal
  (for a given signo) is retained by the system.  This is consistent with
  POSIX which states:  &quot;If a subsequent occurrence of a pending signal
  is generated, it is implementation defined as to whether the signal
  is delivered more than once.&quot;
</p>
<p>
<b>Input Parameters:</b> 
<ul>
<li><I>pid</I>. The id of the task to receive the signal.
  The POSIX <code>kill()</code> specification encodes process group
  information as zero and negative pid values.
  Only positive, non-zero values of pid are supported by this
  implementation. ID of the task to receive signal
<LI><I>signo</I>. The signal number to send.
  If signo is zero, no signal is sent, but all error checking is performed.
</UL>

<p>
  <B>Returned Values:</B> 
  <UL>
    <LI>OK or ERROR
  </UL>
</p>

<p>
  <B>Assumptions/Limitations:</B> 
</p>
<p>
  <b>POSIX  Compatibility:</b>
    Comparable to the POSIX interface of the same name.
    Differences from the POSIX interface include:
</p>
<ul>
  <li>Default action is to ignore signals.</li>
  <li>Signals are processed one at a time in order </li>
  <li>Sending of signals to 'process groups' is not supported in NuttX.</li>
</ul>

<H2>2.9 <A NAME="Pthread">Pthread Interfaces</A></H2>
<p>
  NuttX does not support <i>processes</i> in the way that, say, Linux does.
  NuttX only supports simple threads or tasks running within the same address space.
  For the most part, threads and tasks are interchangeable and differ primarily
  only in such things as the inheritance of file descriptors.
  Basically, threads are initialized and uninitialized differently and share a
  few more resources than tasks.
<p>
  The following pthread interfaces are supported in some form by NuttX:
</p>
<ul>
  <li><a href="#pthreadattrinit">2.9.1 pthread_attr_init</a></li>
  <li><a href="#pthreadattrdestroy">2.9.2 pthread_attr_destroy</a></li>
  <li><a href="#pthreadattrsetschedpolity">2.9.3 pthread_attr_setschedpolicy</a></li>
  <li><a href="#pthreadattrgetschedpolicy">2.9.4 pthread_attr_getschedpolicy</a></li>
  <li><a href="#pthreadattrsetschedparam">2.9.5 pthread_attr_setschedparam</a></li>
  <li><a href="#pthreadattrgetschedparam">2.9.6 pthread_attr_getschedparam</a></li>
  <li><a href="#pthreadattrsetinheritsched">2.9.7 pthread_attr_setinheritsched</a></li>
  <li><a href="#pthreadattrgetinheritsched">2.9.8 pthread_attr_getinheritsched</a></li>
  <li><a href="#pthreadattrsetstacksize">2.9.9 pthread_attr_setstacksize</a></li>
  <li><a href="#pthreadattrgetstacksize">2.9.10 pthread_attr_getstacksize</a></li>
  <li><a href="#pthreadcreate">2.9.11 pthread_create</a></li>
  <li><a href="#pthreaddetach">2.9.12 pthread_detach</a></li>
  <li><a href="#pthreadexit">2.9.13 pthread_exit</a></li>
  <li><a href="#pthreadcancel">2.9.14 pthread_cancel</a></li>
  <li><a href="#pthreadsetcancelstate">2.9.15 pthread_setcancelstate</a></li>
  <li><a href="#pthreadtestcancelstate">2.9.16 pthread_testcancelstate</a></li>
  <li><a href="#pthreadjoin">2.9.17 pthread_join</a></li>
  <li><a href="#pthreadyield">2.9.18 pthread_yield</a></li>
  <li><a href="#pthreadself">2.9.19 pthread_self</a></li>
  <li><a href="#pthreadgetschedparam">2.9.20 pthread_getschedparam</a></li>
  <li><a href="#pthreadsetschedparam">2.9.21 pthread_setschedparam</a></li>
  <li><a href="#pthreadkeycreate">2.9.22 pthread_key_create</a></li>
  <li><a href="#pthreadsetspecific">2.9.23 pthread_setspecific</a></li>
  <li><a href="#pthreadgetspecific">2.9.24 pthread_getspecific</a></li>
  <li><a href="#pthreadkeydelete">2.9.25 pthread_key_delete</a></li>
  <li><a href="#pthreadmutexattrinit">2.9.26 pthread_mutexattr_init</a></li>
  <li><a href="#pthreadmutexattrdestroy">2.9.27 pthread_mutexattr_destroy</a></li>
  <li><a href="#pthreadmutexattrgetpshared">2.9.28 pthread_mutexattr_getpshared</a></li>
  <li><a href="#pthreadmutexattrsetpshared">2.9.29 pthread_mutexattr_setpshared</a></li>
  <li><a href="#pthreadmutexinit">2.9.30 pthread_mutex_init</a></li>
  <li><a href="#pthreadmutexdestrory">2.9.31 pthread_mutex_destroy</a></li>
  <li><a href="#pthreadmutexlock">2.9.32 pthread_mutex_lock</a></li>
  <li><a href="#pthreadmutextrylock">2.9.33 pthread_mutex_trylock</a></li>
  <li><a href="#pthreadmutexunlock">2.9.34 pthread_mutex_unlock</a></li>
  <li><a href="#pthreadconaddrinit">2.9.35 pthread_condattr_init</a></li>
  <li><a href="#pthreadocndattrdestroy">2.9.36 pthread_condattr_destroy</a></li>
  <li><a href="#pthreadcondinit">2.9.37 pthread_cond_init</a></li>
  <li><a href="#pthreadconddestroy">2.9.38 pthread_cond_destroy</a></li>
  <li><a href="#pthreadcondbroadcast">2.9.39 pthread_cond_broadcast</a></li>
  <li><a href="#pthreadcondsignal">2.9.40 pthread_cond_signal</a></li>
  <li><a href="#pthreadcondwait">2.9.41 pthread_cond_wait</a></li>
  <li><a href="#pthreadcondtimedwait">2.9.42 pthread_cond_timedwait</a></li>
  <li><a href="#pthreadbarrierattrinit">2.9.43 pthread_barrierattr_init</a></li>
  <li><a href="#pthreadbarrierattrdestroy">2.9.44 pthread_barrierattr_destroy</a></li>
  <li><a href="#pthreadbarrierattrsetpshared">2.9.45 pthread_barrierattr_setpshared</a></li>
  <li><a href="#pthreadbarrierattrgetpshared">2.9.46 pthread_barrierattr_getpshared</a></li>
  <li><a href="#pthreadbarrierinit">2.9.47 pthread_barrier_init</a></li>
  <li><a href="#pthreadbarrierdestroy">2.9.48 pthread_barrier_destroy</a></li>
  <li><a href="#pthreadbarrierwait">2.9.49 pthread_barrier_wait</a></li>
  <li><a href="#pthreadonce">2.9.50 pthread_once</a></li>
  <li><a href="#pthreadkill">2.9.51 pthread_kill</a></li>
  <li><a href="#pthreadsigmask">2.9.52 pthread_sigmask</a></li>
</ul>
<p>
  No support for the ollowing pthread interfaces is provided by NuttX:
</p>
<ul>
  <li><code>pthread_atfork</code>. register fork handlers.</li>
  <li><code>pthread_attr_getdetachstate</code>. get and set the detachstate attribute.</li>
  <li><code>pthread_attr_getguardsize</code>. get and set the thread guardsize attribute.</li>
  <li><code>pthread_attr_getinheritsched</code>. get and set the inheritsched attribute.</li>
  <li><code>pthread_attr_getscope</code>. get and set the contentionscope attribute.</li>
  <li><code>pthread_attr_getstack</code>. get and set stack attributes.</li>
  <li><code>pthread_attr_getstackaddr</code>. get and set the stackaddr attribute.</li>
  <li><code>pthread_attr_setdetachstate</code>. get and set the detachstate attribute.</li>
  <li><code>pthread_attr_setguardsize</code>. get and set the thread guardsize attribute.</li>
  <li><code>pthread_attr_setscope</code>. get and set the contentionscope attribute.</li>
  <li><code>pthread_attr_setstack</code>. get and set stack attributes.</li>
  <li><code>pthread_attr_setstackaddr</code>. get and set the stackaddr attribute.</li>
  <li><code>pthread_barrier_destroy</code>. destroy and initialize a barrier object.</li>
  <li><code>pthread_barrier_init</code>. destroy and initialize a barrier object.</li>
  <li><code>pthread_barrier_wait</code>. synchronize at a barrier.</li>
  <li><code>pthread_cleanup_pop</code>. establish cancellation handlers.</li>
  <li><code>pthread_cleanup_push</code>. establish cancellation handlers.</li>
  <li><code>pthread_condattr_getclock</code>. get and set the clock selection condition variable attribute.</li>
  <li><code>pthread_condattr_getpshared</code>. get and set the process-shared condition variable attributes.</li>
  <li><code>pthread_condattr_setclock</code>. get and set the clock selection condition variable attribute.</li>
  <li><code>pthread_condattr_setpshared</code>. get and set the process-shared condition variable attributes.</li>
  <li><code>pthread_getconcurrency</code>. get and set the level of concurrency.</li>
  <li><code>pthread_getcpuclockid</code>. access a thread CPU-time clock.</li>
  <li><code>pthread_mutex_getprioceiling</code>. get and set the priority ceiling of a mutex.</li>
  <li><code>pthread_mutex_setprioceiling</code>. get and set the priority ceiling of a mutex.</li>
  <li><code>pthread_mutex_timedlock</code>. lock a mutex.</li>
  <li><code>pthread_mutexattr_getprioceiling</code>. get and set the prioceiling attribute of the mutex attributes object.</li>
  <li><code>pthread_mutexattr_getprotocol</code>. get and set the protocol attribute of the mutex attributes object.</li>
  <li><code>pthread_mutexattr_gettype</code>. get and set the mutex type attribute.</li>
  <li><code>pthread_mutexattr_setprioceiling</code>. get and set the prioceiling attribute of the mutex attributes object.</li>
  <li><code>pthread_mutexattr_setprotocol</code>. get and set the protocol attribute of the mutex attributes object.</li>
  <li><code>pthread_mutexattr_settype</code>. get and set the mutex type attribute.</li>
  <li><code>pthread_rwlock_destroy</code>. destroy and initialize a read-write lock object.</li>
  <li><code>pthread_rwlock_init</code>. destroy and initialize a read-write lock object.</li>
  <li><code>pthread_rwlock_rdlock</code>. lock a read-write lock object for reading.</li>
  <li><code>pthread_rwlock_timedrdlock</code>. lock a read-write lock for reading.</li>
  <li><code>pthread_rwlock_timedwrlock</code>. lock a read-write lock for writing.</li>
  <li><code>pthread_rwlock_tryrdlock</code>. lock a read-write lock object for reading.</li>
  <li><code>pthread_rwlock_trywrlock</code>. lock a read-write lock object for writing.</li>
  <li><code>pthread_rwlock_unlock</code>. unlock a read-write lock object.</li>
  <li><code>pthread_rwlock_wrlock</code>. lock a read-write lock object for writing.</li>
  <li><code>pthread_rwlockattr_destroy</code>. destroy and initialize the read-write lock attributes object.</li>
  <li><code>pthread_rwlockattr_getpshared</code>. get and set the process-shared attribute of the read-write lock attributes object.</li>
  <li><code>pthread_rwlockattr_init</code>. destroy and initialize the read-write lock attributes object.</li>
  <li><code>pthread_rwlockattr_setpshared</code>. get and set the process-shared attribute of the read-write lock attributes object.</li>
  <li><code>pthread_setcanceltype</code>. set cancelability state.</li>
  <li><code>pthread_setconcurrency</code>. get and set the level of concurrency.</li>
  <li><code>pthread_spin_destroy</code>. destroy or initialize a spin lock object.</li>
  <li><code>pthread_spin_init</code>. destroy or initialize a spin lock object.</li>
  <li><code>pthread_spin_lock</code>. lock a spin lock object.</li>
  <li><code>pthread_spin_trylock</code>. lock a spin lock object.</li>
  <li><code>pthread_spin_unlock</code>. unlock a spin lock object.</li>
  <li><code>pthread_testcancel</code>. set cancelability state.</li>
</ul>

<H3><a name="pthreadattrinit">2.9.1 pthread_attr_init</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_attr_init(pthread_attr_t *attr);
</PRE>
<P>
<B>Description:</B>
Initializes a thread attributes object (attr) with default values
for all of the individual attributes used by the implementation.
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_init()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.
<P>
<H3><a name="pthreadattrdestroy">2.9.2 pthread_attr_destroy</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_attr_destroy(pthread_attr_t *attr);
</PRE>
<P>
<B>Description:</B>
An attributes object can be deleted when it is no longer needed.
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_destroy()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.
<P>
<H3><a name="pthreadattrsetschedpolity">2.9.3 pthread_attr_setschedpolicy</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_setschedpolicy()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadattrgetschedpolicy">2.9.4 pthread_attr_getschedpolicy</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_attr_getschedpolicy(pthread_attr_t *attr, int *policy);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_getschedpolicy()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadattrsetschedparam">2.9.5 pthread_attr_getschedpolicy</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
   #include &lt;pthread.h&gt;
    int pthread_attr_setschedparam(pthread_attr_t *attr,
				      const struct sched_param *param);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_getschedpolicy()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadattrgetschedparam">2.9.6 pthread_attr_getschedparam</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
   #include &lt;pthread.h&gt;
     int pthread_attr_getschedparam(pthread_attr_t *attr,
				      struct sched_param *param);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_getschedparam()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadattrsetinheritsched">2.9.7 pthread_attr_setinheritsched</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
   #include &lt;pthread.h&gt;
    int pthread_attr_setinheritsched(pthread_attr_t *attr,
					int inheritsched);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_setinheritsched()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.
<P>
<H3><a name="pthreadattrgetinheritsched">2.9.8 pthread_attr_getinheritsched</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
   #include &lt;pthread.h&gt;
     int pthread_attr_getinheritsched(const pthread_attr_t *attr,
					int *inheritsched);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_getinheritsched()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadattrsetstacksize">2.9.9 pthread_attr_setstacksize</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
   #include &lt;pthread.h&gt;
    int pthread_attr_setstacksize(pthread_attr_t *attr, long stacksize);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_setstacksize()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadattrgetstacksize">2.9.10 pthread_attr_getstacksize</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
   int pthread_attr_getstacksize(pthread_attr_t *attr, long *stackaddr);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_attr_getstacksize()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadcreate">2.9.11 pthread_create</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_create(pthread_t *thread, pthread_attr_t *attr,
			  pthread_startroutine_t startRoutine,
			  pthread_addr_t arg);
</PRE>
<P>
<B>Description:</B>
To create a thread object and runnable thread, a routine
must be specified as the new thread's start routine.  An
argument may be passed to this routine, as an untyped
address; an untyped address may also be returned as the
routine's value.  An attributes object may be used to
specify details about the kind of thread being created.
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_create()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreaddetach">2.9.12 pthread_detach</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_detach(pthread_t thread);
</PRE>
<P>
<B>Description:</B>
A thread object may be "detached" to specify that the
return value and completion status will not be requested.
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_detach()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadexit">2.9.13 pthread_exit</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    void pthread_exit(pthread_addr_t pvValue);
</PRE>
<P>
<B>Description:</B>
A thread may terminate it's own execution.
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_exit()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadcancel">2.9.14 pthread_cancel</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_cancel(pthread_t thread);
</PRE>
<P>
<B>Description:</B>

<p>The  pthread_cancel() function shall request that thread
be canceled. The target thread's cancelability state determines
when the cancellation takes effect. When the
cancellation is acted on, thread shall be terminated.</p>

<p>When cancelability is disabled, all cancels are held pending
in the target thread until the thread changes the cancelability.
When cancelability is deferred, all cancels are held pending in
the target thread until the thread changes the cancelability or
calls pthread_testcancel().</p>

<p>Cancelability is asynchronous; all cancels are acted upon
immediately (when enable), interrupting the thread with its processing.</p>

<P>
<B>Input Parameters:</B>
<P>
<UL>
<LI><I>thread</I>.
Identifies the thread to be canceled.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>ptnread_cancel()</I> function will return zero (<I>OK</I>).
Otherwise, an error number will be returned to indicate the error:
<P>
<UL>
<LI><I>ESRCH</I>.
No thread could be found corresponding to that specified by the given thread ID.</li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.  Except:</p>
<UL>
<LI>The thread-specific data destructor functions shall be called for thread.
However, these destructors are not currently supported.</li>
<li>Cancellation types are not supported.  The thread will be canceled
at the time that pthread_cancel() is called or, if cancelation is disabled, at
the time when cancelation is re-enabled.</li>
<li><tt>pthread_testcancel()</tt> is not supported.</li>
<li>Thread cancellation at <i>cancellation points</i> is not supported.</li>
</UL>

<H3><a name="pthreadsetcancelstate">2.9.15 pthread_setcancelstate</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_setcancelstate(int state, int *oldstate);
</PRE>
<P>
<B>Description:</B>
<P>The <i>pthread_setcancelstate()</i> function atomically
sets both the calling thread's cancelability state to the indicated
state and returns the previous cancelability  state at the location
referenced by oldstate.
Legal values for state are PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DISABLE.<.li>

<p>Any pending thread cancelation may occur at the time that the
cancelation state is set to PTHREAD_CANCEL_ENABLE.</p>

<B>Input Parameters:</B>
<P>
<UL>
<LI><I>state</I> 
New cancelation state.  One of PTHREAD_CANCEL_ENABLE or PTHREAD_CANCEL_DISABLE.<.li>
<LI><I>oldstate</I>.
Location to return the previous cancelation state.
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_setcancelstate()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be returned to indicate the error:
<P>
<UL>
<LI><I>ESRCH</I>.
No thread could be found corresponding to that specified by the given thread ID.</li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadtestcancelstate">2.9.16 pthread_testcancelstate</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_setcancelstate(void);
</PRE>
<P>
<B>Description:</B>
<P><b>NOT SUPPORTED</b>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_setcancelstate()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadjoin">2.9.17 pthread_join</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_join(pthread_t thread, pthread_addr_t *ppvValue);
</PRE>
<P>
<B>Description:</B>
A thread can await termination of another thread and retrieve
the return value of the thread.
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_join()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadyield">2.9.18 pthread_yield</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    void pthread_yield(void);
</PRE>
<P>
<B>Description:</B>
A thread may tell the scheduler that its processor can be
made available.
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_yield()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadself">2.9.19 pthread_self</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    pthread_t pthread_self(void);
</PRE>
<P>
<B>Description:</B>
A thread may obtain a copy of its own thread handle.
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_self()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadgetschedparam">2.9.20 pthread_getschedparam</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_getschedparam(pthread_t thread, int *policy,
                              struct sched_param *param);
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_getschedparam()</code> functions will get the 
  scheduling policy and parameters of threads.
  For <code>SCHED_FIFO</code> and <code>SCHED_RR</code>, the only
  required member of the <code>sched_param</code> structure is the
  priority <code>sched_priority</code>.
</p>
<p>
  The <code>pthread_getschedparam()</code> function will retrieve the
  scheduling policy and scheduling parameters for the thread whose thread
  ID is given by <code>thread</code> and will store those values in
  <code>policy</code> and <code>param</code>, respectively.
  The priority value returned from <code>pthread_getschedparam()</code>
  will be the value specified by the most recent <code>pthread_setschedparam()</code>,
  <code>pthread_setschedprio()</code>, or <code>pthread_create()</code> call
  affecting the target thread.
  It will not reflect any temporary adjustments to its priority (such as might
  result of any priority inheritance, for example).
</p>
<p>
  The policy parameter may have the value <code>SCHED_FIFO</code> or <code>SCHED_RR</code>
  (<code>SCHED_OTHER</code> and <code>SCHED_SPORADIC</code>, in particular, are not supported).
  The <code>SCHED_FIFO</code> and <code>SCHED_RR<code> policies will have a single
  scheduling parameter, <code>sched_priority</code>.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li>
    <code>thread</code>.
    The ID of thread whose scheduling parameters will be queried.
  </li>
  <li>
    <code>policy</code>.
    The location to store the thread's scheduling policy.
  </li>
  <li>
    <code>param</code>.
    The location to store the thread's priority.
  </li>
</ul>
<p>
  <b>Returned Values:</b>
  0 (<code>OK</code>) if successful.
  Otherwise, the error code <code>ESRCH</code> if the value specified by
  <code>thread</code> does not refer to an existing thread.
</p>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b>
  Comparable to the POSIX interface of the same name.
</p>

<H3><a name="pthreadsetschedparam">2.9.21 pthread_setschedparam</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_setschedparam(pthread_t thread, int policy,
                              const struct sched_param *param);
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_setschedparam()</code> functions will set the scheduling policy
  and parameters of threads.
  For <code>SCHED_FIFO</code> and <code>SCHED_RR</code>, the only required member
  of the <code>sched_param</code> structure is the priority <code>sched_priority</code>.
</p>
</p>
  The <code>pthread_setschedparam()</code> function will set the scheduling policy
  and associated scheduling parameters for the thread whose thread ID is given by
  <code>thread</code> to the policy and associated parameters provided in
  <code>policy</code> and <code>param</code>, respectively.
</p>
<p>
  The policy parameter may have the value <code>SCHED_FIFO</code> or <code>SCHED_RR</code>.
  (<code>SCHED_OTHER</code> and <code>SCHED_SPORADIC</code>, in particular, are not supported).
  The <code>SCHED_FIFO</code> and <code>SCHED_RR</code> policies will have a single
  scheduling parameter, <code>sched_priority</code>.
</p>
<p>
  If the <code>pthread_setschedparam()</code> function fails, the scheduling
  parameters will not be changed for the target thread.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li>
    <code>thread</code>.
    The ID of thread whose scheduling parameters will be modified.
  </li>
  <li>
    <code>policy</code>.
    The new scheduling policy of the thread.
    Either <code>SCHED_FIFO</code> or <code>SCHED_RR<code>.
    <code>SCHED_OTHER<code> and <code>SCHED_SPORADIC<code> are not supported.
  </li>
  <li>
    <code>param</code>.
    The location to store the thread's priority.
  </li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <I>pthread_setschedparam()</I> function will return
  zero (<I>OK</I>).  Otherwise, an error number will be
  returned to indicate the error:
</p>
<ul>
  <li>
    <code>EINVAL</code>.
    The value specified by <code>policy</code> or one of the scheduling parameters
    associated with the scheduling policy <code>policy</code> is invalid.
  </li>
  <li>
    <code>ENOTSUP</code>.
    An attempt was made to set the policy or scheduling parameters to an unsupported
    value (<code>SCHED_OTHER</code> and <code>SCHED_SPORADIC</code> in particular are
    not supported)
  </li>
  <li>
    <code>EPERM</code>.
    The caller does not have the appropriate permission to set either the scheduling
    parameters or the scheduling policy of the specified thread.
    Or, the implementation does not allow the application to modify one of the
    parameters to the value specified.

  </li>
  <li>
    <code>ESRCH</code>.
    The value specified by thread does not refer to a existing thread.
  </li>
</ul>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b>
  Comparable to the POSIX interface of the same name.
</p>

<H3><a name="pthreadkeycreate">2.9.22 pthread_key_create</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_key_create( pthread_key_t *key, void (*destructor)(void*) )
</PRE>
<P>
<B>Description:</B>
<P>
This function creates a thread-specific data key visible
to all threads in the system.  Although the same key value
may be used by different threads, the values bound to
the key by <I>pthread_setspecific()</I> are maintained on a
per-thread basis and persist for the life of the calling
thread.
<P>
Upon key creation, the value <I>NULL</I> will be associated with
the the new key in all active threads.  Upon thread
creation, the value <I>NULL</I> will be associated with all
defined keys in the new thread.
<P>
<B>Input Parameters:</B>
<P>
<UL>
<LI><I>key</I> is a pointer to the key to create.
<LI><I>destructor</I> is an optional destructor() function that may
be associated with each key that is invoked when a
thread exits.  However, this argument is ignored in
the current implementation.
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_key_create()</I> function will
store the newly created key value at *<I>key</I> and return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
<LI><I>EAGAIN</I>.  The system lacked sufficient resources
to create another thread-specific data key, or the
system-imposed limit on the total number of keys
per task {<I>PTHREAD_KEYS_MAX</I>} has been exceeded
<LI><I>ENONMEM</I>  Insufficient memory exists to create the key.
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.
<UL>
<LI>The present implementation ignores the destructor argument.
</UL>

<H3><a name="pthreadsetspecific">2.9.23 pthread_setspecific</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_setspecific( pthread_key_t key, void *value )
</PRE>
<P>
<B>Description:</B>
<P>
The <I>pthread_setspecific()</I> function associates a thread-
specific value with a key obtained via a previous call
to <I>pthread_key_create()</I>.  Different threads may bind
different values to the same key.  These values are
typically pointers to blocks of dynamically allocated
memory that have been reserved for use by the calling
thread.
<P>
The effect of calling <I>pthread_setspecific()</I> with a key value
not obtained from <I>pthread_key_create()</I> or after a key has been
deleted with <I>pthread_key_delete()</I> is undefined.
<P>
<B>Input Parameters:</B>
<P>
<UL>
<LI><I>key</I>.  The data key to set the binding for.
<LI><I>value</I>. The value to bind to the key.
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, <I>pthread_setspecific()</I> will return zero (<I>OK</I>).
Otherwise, an error number will be returned:
<P>
<UL>
<LI><I>ENOMEM</I>.  Insufficient memory exists to associate the value
with the key.
<LI><I>EINVAL</I>.  The key value is invalid.
</UL>
<P>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.
<UL>
<LI>pthread_setspecific() may be called from a thread-specific data
destructor function.
</UL>

<H3><a name="pthreadgetspecific">2.9.24 pthread_getspecific</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    void *pthread_getspecific( pthread_key_t key )
</PRE>
<P>
<B>Description:</B>
<P>
The <I>pthread_getspecific()</I> function returns the value
currently bound to the specified key on behalf of the
calling thread.
<P>
The effect of calling <I>pthread_getspecific()</I> with a key value
not obtained from <I>pthread_key_create()</I> or after a key has been
deleted with <I>pthread_key_delete()</I> is undefined.
<P>
<B>Input Parameters:</B>
<P>
<UL>
<LI><I>key</I>.  The data key to get the binding for.
</UL>
<P>
<B>Returned Values:</B>
<P>
The function <I>pthread_getspecific()</I> returns the thread-
specific data associated with the given key.  If no
thread specific data is associated with the key, then
the value <I>NULL</I> is returned.
<P>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.
<UL>
<LI>pthread_getspecific() may be called from a thread-specific data
destructor function.
</UL>

<H3><a name="pthreadkeydelete">2.9.25 pthread_key_delete</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_key_delete( pthread_key_t key )
</PRE>
<P>
<B>Description:</B>
<P>
This POSIX function should delete a thread-specific data
key previously returned by <I>pthread_key_create()</I>.  However,
this function does nothing in the present implementation.
<P>
<B>Input Parameters:</B>
<P>
<UL>
<LI><I>key</I>.  The key to delete
</UL>
<P>
<B>Returned Values:</B>
<P>
<UL>
<LI>Always returns <I>EINVAL</I>.
</UL>
<P>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutexattrinit">2.9.26 pthread_mutexattr_init</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_mutexattr_init(pthread_mutexattr_t *attr);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutexattr_init()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutexattrdestroy">2.9.27 pthread_mutexattr_destroy</A></H3>
<P>
<B>Function Protoype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_mutexattr_destroy(pthread_mutexattr_t *attr);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutexattr_destroy()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutexattrgetpshared">2.9.28 pthread_mutexattr_getpshared</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_mutexattr_getpshared(pthread_mutexattr_t *attr,
					int *pshared);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutexattr_getpshared()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutexattrsetpshared">2.9.29 pthread_mutexattr_setpshared</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
   int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr,
					int pshared);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutexattr_setpshared()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutexinit">2.9.30 pthread_mutex_init</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_mutex_init(pthread_mutex_t *mutex,
			      pthread_mutexattr_t *attr);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutex_init()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutexdestrory">2.9.31 pthread_mutex_destroy</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_mutex_destroy(pthread_mutex_t *mutex);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutex_destroy()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutexlock">2.9.32 pthread_mutex_lock</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_mutex_lock(pthread_mutex_t *mutex);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutex_lock()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutextrylock">2.9.33 pthread_mutex_trylock</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_mutex_trylock(pthread_mutex_t *mutex);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutex_trylock()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadmutexunlock">2.9.34 pthread_mutex_unlock</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_mutex_unlock(pthread_mutex_t *mutex);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_mutex_unlock()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadconaddrinit">2.9.35 pthread_condattr_init</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_condattr_init(pthread_condattr_t *attr);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_condattr_init()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadocndattrdestroy">2.9.36 pthread_condattr_destroy</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_condattr_destroy(pthread_condattr_t *attr);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_condattr_destroy()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadcondinit">2.9.37 pthread_cond_init</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *attr);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_cond_init()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadconddestroy">2.9.38 pthread_cond_destroy</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_cond_destroy(pthread_cond_t *cond);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_cond_destroy()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadcondbroadcast">2.9.39 pthread_cond_broadcast</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_cond_broadcast(pthread_cond_t *cond);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_cond_broadcast()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadcondsignal">2.9.40 pthread_cond_signal</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_cond_signal(pthread_cond_t *dond);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
<B>Returned Values:</B>
<P>
If successful, the <I>pthread_cond_signal()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadcondwait">2.9.41 pthread_cond_wait</A></H3>
<P>
<B>Function Prototype:</B>
<P>
<PRE>
    #include &lt;pthread.h&gt;
    int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
</PRE>
<P>
<B>Description:</B>
<P>
<B>Input Parameters:</B>
<P>
<UL>
  <li><code>param<code>.</li>
</UL>
<P>
  <b>Returned Values:</b>
<P>
If successful, the <I>pthread_cond_wait()</I> function will return
zero (<I>OK</I>).  Otherwise, an error number will be
returned to indicate the error:
<P>
<UL>
  <li><code>Exxx</code>. </li>
</UL>
<B>Assumptions/Limitations:</B>
<P>
<B>POSIX Compatibility:</B> Comparable to the POSIX
interface of the same name.

<H3><a name="pthreadcondtimedwait">2.9.42 pthread_cond_timedwait</A></H3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
				  const struct timespec *abstime);
</pre>
<p>
  <b>Description:</b>
</p>
<p>
  <b>Input Parameters:</b>
</p>
<p>
<ul>
  <li><code>parm</code>.</li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  If successful, the <code>pthread_cond_timedwait()</code> function will return
  zero (<code>OK</code>).  Otherwise, an error number will be
  returned to indicate the error:
</p>
<ul>
  <li><code>Exxx</code>. </li>
</ul>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadbarrierattrinit">2.9.43 pthread_barrierattr_init</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_barrierattr_init(FAR pthread_barrierattr_t *attr);
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_barrierattr_init()</code> function will initialize a barrier
  attribute object <code>attr</code> with the default value for all of the attributes
  defined by the implementation.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li>
    <code>attr</code>. Barrier attributes to be initialized.
</li>
</ul>
<p>
  <b>Returned Values:</b>
  0 (<code>OK</code>) on success or <code>EINVAL</code> if <code>attr</code> is invalid.
</p>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadbarrierattrdestroy">2.9.44 pthread_barrierattr_destroy</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_barrierattr_destroy(FAR pthread_barrierattr_t *attr);
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_barrierattr_destroy()</code> function will destroy a barrier attributes object.
  A destroyed attributes object can be reinitialized using <code>pthread_barrierattr_init()</code>;
  the results of otherwise referencing the object after it has been destroyed are undefined.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li>
    <code>attr</code>. Barrier attributes to be destroyed.
</li>
</ul>
<p>
  <b>Returned Values:</b> 0 (OK) on success or EINVAL if attr is invalid.
</p>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadbarrierattrsetpshared">2.9.45 pthread_barrierattr_setpshared</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_barrierattr_setpshared(FAR pthread_barrierattr_t *attr, int pshared);
</pre>
<p>
  <b>Description:</b>
  The process-shared attribute is set to <code>PTHREAD_PROCESS_SHARED</code> to permit
  a barrier to be operated upon by any thread that has access to the memory where the
  barrier is allocated.
  If the process-shared attribute is <code>PTHREAD_PROCESS_PRIVATE</code>, the barrier can
  only be operated upon by threads created within the same process as the thread that
  initialized the barrier.
  If threads of different processes attempt to operate on such a barrier, the behavior is undefined.
  The default value of the attribute is <code>PTHREAD_PROCESS_PRIVATE</code>.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>attr</code>. Barrier attributes to be modified.</li>
  <li><code>pshared</code>. The new value of the pshared attribute.</li>
</ul>
<p>
  <b>Returned Values:</b>  0 (<code>OK</code>) on success or <code>EINVAL</code> if either
  <code>attr</code> is invalid or <code>pshared</code> is not one of
  <code>PTHREAD_PROCESS_SHARED</code> or <code>PTHREAD_PROCESS_PRIVATE</code>.
</p>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadbarrierattrgetpshared">2.9.46 pthread_barrierattr_getpshared</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_barrierattr_getpshared(FAR const pthread_barrierattr_t *attr, FAR int *pshared);
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_barrierattr_getpshared()</code> function will obtain the value of the
  process-shared attribute from the attributes object referenced by <code>attr</code>.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<p>
<ul>
  <li><code>attr</code>. Barrier attributes to be queried.</li>
  <li><code>pshared</code>. The location to stored the current value of the pshared attribute.</li>
</ul>
<p>
  <b>Returned Values:</b> 0 (<code>OK</code>) on success or <code>EINVAL</code> if
  either <code>attr</code> or <code>pshared</code> is invalid.
</p>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadbarrierinit">2.9.47 pthread_barrier_init</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_barrier_init(FAR pthread_barrier_t *barrier,
                             FAR const pthread_barrierattr_t *attr, unsigned int count);
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_barrier_init()</code> function allocates any resources required to
  use the barrier referenced by <code>barrier</code> and initialized the barrier with
  the attributes referenced by <code>attr</code>. 
  If <code>attr</code> is NULL, the default barrier attributes will be used.
  The results are undefined if <code>pthread_barrier_init()</code> is called when any
  thread is blocked on the barrier.
  The results are undefined if a barrier is used without first being initialized.
  The results are undefined if <code>pthread_barrier_init()</code> is called specifying
  an already initialized barrier.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li>
    <code>barrier</code>.
    The barrier to be initialized.
  </li>
  <li>
    <code>attr</code>.
    Barrier attributes to be used in the initialization.
  </li>
  <li>
    <code>count</code>.
    The count to be associated with the barrier.
    The count argument specifies the number of threads that must call
    <code>pthread_barrier_wait()</code> before any of them successfully return from the call.
    The value specified by count must be greater than zero.
  </li>
</ul>
<p>
  <b>Returned Values:</b>0 (OK) on success or on of the following error numbers:
</p>
<ul>
  <li>
    <code>EAGAIN</code>.
    The system lacks the necessary resources to initialize another barrier.
  </li>
  <li>
    <code>EINVAL</code>.
    The barrier reference is invalid, or the values specified by attr are invalid, or
    the value specified by count is equal to zero.
  </li>
  <li>
    <code>ENOMEM</code>.
    Insufficient memory exists to initialize the barrier.
  </li>
  <li>
    <code>EBUSY</code>.
    The implementation has detected an attempt to reinitialize a barrier while it is in use.
  </li>
</ul>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadbarrierdestroy">2.9.48 pthread_barrier_destroy</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_barrier_destroy(FAR pthread_barrier_t *barrier);
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_barrier_destroy()</code> function destroys the barrier referenced
  by <code>barrie</code> and releases any resources used by the barrier.
  The effect of subsequent use of the barrier is undefined until the barrier is
  reinitialized by another call to <code>pthread_barrier_init()</code>.
  The results are undefined if <code>pthread_barrier_destroy()</code> is called when
  any thread is blocked on the barrier, or if this function is called with an
  uninitialized barrier.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>barrier</code>. The barrier to be destroyed.</li>
</ul>
<p>
  <b>Returned Values:</b> 0 (<code>OK</code>) on success or on of the following error numbers:
</p>
<ul>
  <li>
    <code>EBUSY</code>.
    The implementation has detected an attempt to destroy a barrier while it is in use.
  </li>
  <li>
    <code>EINVAL</code>.
    The value specified by barrier is invalid.
  </li>
</ul>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadbarrierwait">2.9.49 pthread_barrier_wait</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_barrier_wait(FAR pthread_barrier_t *barrier);
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_barrier_wait()</code> function synchronizse participating
  threads at the barrier referenced by <code>barrier</code>.
  The calling thread is blocked until the required number of threads have called
  <code>pthread_barrier_wait()</code> specifying the same <code>barrier</code>.
  When the required number of threads have called <code>pthread_barrier_wait()</code>
  specifying the <code>barrier</code>, the constant <code>PTHREAD_BARRIER_SERIAL_THREAD</code>
  will be returned to one unspecified thread and zero will be returned to each of
  the remaining threads.
  At this point, the barrier will be reset to the state it had as a result of the most
  recent <code>pthread_barrier_init()</code> function that referenced it.
</p>
<p>
  The constant <code>PTHREAD_BARRIER_SERIAL_THREAD</code> is defined in 
 <code>pthread.h</code> and its value must be distinct from any other value
  returned by <code>pthread_barrier_wait()</code>.
</p>
<p>
  The results are undefined if this function is called with an uninitialized barrier.
</p>
<p>
  If a signal is delivered to a thread blocked on a barrier, upon return from the
  signal handler the thread will resume waiting at the barrier if the barrier wait
  has not completed.
  Otherwise, the thread will continue as normal from the completed barrier wait.
  Until the thread in the signal handler returns from it, it is unspecified whether
  other threads may proceed past the barrier once they have all reached it.
</p>
<p>
  A thread that has blocked on a barrier will not prevent any unblocked thread that
  is eligible to use the same processing resources from eventually making forward
  progress in its execution.
  Eligibility for processing resources will be determined by the scheduling policy.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<ul>
  <li><code>barrier</code>. The barrier on which to wait.</li>
</ul>
<p>
  <b>Returned Values:</b> 0 (<code>OK</code>) on success or <code>EINVAL</code> if the barrier is not valid.
</p>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>


<h3><a name="pthreadonce">2.9.50 pthread_once</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;pthread.h&gt;
    int pthread_once(FAR pthread_once_t *once_control, CODE void (*init_routine)(void));
</pre>
<p>
  <b>Description:</b>
  The  first  call to <code>pthread_once()</code> by any thread with a given
  <code>once_control</code>, will call the <code>init_routine()</code> with no arguments.
  Subsequent calls to <code>pthread_once()</code> with the same <code>once_control</code> will have no effect.
  On return from <code>pthread_once()</code>, <code>init_routine()</code> will have completed.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<p>
<ul>
  <li>
    <code>once_control</code>.
    Determines if <code>init_routine()</code> should be called.
    <code>once_control</code> should be declared and intialized as follows:
    <ul><pre>pthread_once_t once_control = PTHREAD_ONCE_INIT;
    </pre></ul>
    <code>PTHREAD_ONCE_INIT</code> is defined in <code>pthread.h</code>.
  </li>
  <li>
    <code>init_routine</code>.
    The initialization routine that will be called once.
  </li>
</ul>
<p>
  <b>Returned Values:</b>
  0 (OK) on success or EINVAL if either once_control or init_routine are invalid.
</p>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadkill">2.9.51 pthread_kill</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;signal.h&gt;
    #include &lt;pthread.h&gt;
    int pthread_kill(pthread_t thread, int signo)
</pre>
<p>
  <b>Description:</b>
  The <code>pthread_kill()</code> system call can be used to send any
  signal to a thread.  See <code>kill()</code> for further information
  as this is just a simple wrapper around the <code>kill()</code>
  function.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<p>
<ul>
  <li>
    <code>thread</code>.
    The id of the thread to receive the signal. Only positive, non-zero values of <code>tthread</code>t are supported.
  </li>
  <li>
    <code>signo</code>.
    The signal number to send.  If <code>signo</code> is zero, no signal is sent, but all error checking is performed.
  </li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  On success, the signal was sent and zero is returned.
  On error one of the following error numbers is returned.
</p>
<ul>
  <li>
    <code>EINVAL</code>.
    An invalid signal was specified.
  </li>
  <li>
    <code>EPERM</code>.
    The thread does not have permission to send the signal to the target thread.
  </li>
  <li>
    <code>ESRCH</code>.
    No thread could be found corresponding to that specified by the given thread ID.
  </li>
  <li>
    <code>ENOSYS</code>.
    Do not support sending signals to process groups.
  </li>
</ul>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<h3><a name="pthreadsigmask">2.9.52 pthread_sigmask</a></h3>
<p>
  <b>Function Prototype:</b>
</p>
<pre>
    #include &lt;signal.h&gt;
    #include &lt;pthread.h&gt;
    int pthread_sigmask(int how, FAR const sigset_t *set, FAR sigset_t *oset);
</pre>
<p>
  <b>Description:</b>
  This function is a simple wrapper around <code>sigprocmask()</code>.
  See the <code>sigprocmask()</code> function description for further information.
</p>
<p>
  <b>Input Parameters:</b>
</p>
<p>
<ul>
  <li>
    <code>how</code>. How the signal mast will be changed:
    <ul>
      <li>
        <code>SIG_BLOCK</code>:
        The resulting set is the union of the current set and the signal set pointed to by <code>set</code>.
      </li>
      <li>
        <code>SIG_UNBLOCK</code>:
        The resulting set is the intersection of the current set and the complement of the signal set pointed to by <code>set</code>.
      </li>
      <li>
        <code>SIG_SETMASK</code>:
        The resulting set is the signal set pointed to by <code>set</code>.
      </li>
    </ul>
  </li>
  <li>
    <code>set</code>. Location of the new signal mask.
  </li>
  <li>
    <code>oset</code>. Location to store the old signal mask.
  </li>
</ul>
<p>
  <b>Returned Values:</b>
</p>
<p>
  0 (OK) on succes or EINVAL if <code>how</code> is invalid.
</p>
<p>
  <b>Assumptions/Limitations:</b>
</p>
<p>
  <b>POSIX Compatibility:</b> Comparable to the POSIX interface of the same name.
</p>

<HR>
<H1>3.0 <A NAME="Data_Structures">OS Data Structures</A></H1>
<H2>3.1 Scalar types</H2>
<P>
Many of the types used to communicate with NuttX are simple
scalar types. These types are used to provide architecture independence
of the OS from the application. The scalar types used at the NuttX
interface include:
<UL>
<LI>pid_t
<LI>size_t
<LI>sigset_t
<LI>STATUS
<LI>time_t
</UL>

<H2>3.2 Hidden Interface Structures</H2>
<P>
Several of the types used to interface with NuttX are
structures that are intended to be hidden from the application.
From the standpoint of the application, these structures (and
structure pointers) should be treated as simple handles to reference
OS resources. These hidden structures include:
<UL>
<LI>_TCB
<LI>mqd_t
<LI>sem_t
<LI>WDOG_ID
<LI>pthread_key_t
</UL>
<P>
In order to maintain portability, applications should not reference
specific elements within these hidden structures. These hidden
structures will not be described further in this user's manual.
<P>

<H2>3.3. Access to the <I>errno</I> Variable</H2>
<P>
A pointer to the thread-specific <I>errno</I>. value is available through a
function call:
<P>
<B>Function Prototype:</B>
<P>
<PRE>    int *get_errno_ptr( void )</PRE>
<P>
<B>Description</B>:  <I>osGetErrnorPtr()</I> returns a pointer to
the thread-specific <I>errno</I> value.
<P>
This differs somewhat from the use for errno in a multi-threaded process environment:
Each pthread will have its own private copy of errno and the errno will not be shared
between pthreads.
<P>
<B>Input Parameters</B>:  None
<P>
<B>Returned Values</B>:
<P>
<UL>
<LI>A pointer to the thread-specific <I>errno</I> value.
</UL>
<P>

<H2>3.4 User Interface Structures</H2>
<P>
<H3>3.4.1 main_t</H3>
<P>
main_t defines the type of a task entry point. main_t is declared
in sys/types.h as:
<PRE>
    typedef int (*main_t)(int argc, char *argv[]);
</PRE>

<H3>3.4.2 struct sched_param</H3>

<P>
This structure is used to pass scheduling priorities to and from
NuttX;
<PRE>
    struct sched_param
    {
      int sched_priority;
    };
</PRE>

<H3>3.4.3 struct timespec</H3>

<P>
This structure is used to pass timing information between the
NuttX and a user application:
<PRE>
    struct timespec
    {
      time_t tv_sec;  /* Seconds */
      long   tv_nsec; /* Nanoseconds */
    };
</PRE>

<H3>3.4.4 struct mq_attr</H3>

<P>
This structure is used to communicate message queue attributes
between NuttX and a MoBY application:
<PRE>
    struct mq_attr {
      size_t       mq_maxmsg;   /* Max number of messages in queue */
      size_t       mq_msgsize;  /* Max message size */
      unsigned     mq_flags;    /* Queue flags */
      size_t       mq_curmsgs;  /* Number of messages currently in queue */
    };
</PRE>

<H3>3.4.5 struct sigaction</H3>

<P>
The following structure defines the action to take for given signal:
<PRE>
    struct sigaction
    {
      union
      {
        void (*_sa_handler)(int);
        void (*_sa_sigaction)(int, siginfo_t *, void *);
      } sa_u;
      sigset_t           sa_mask;
      int                sa_flags;
    };
    #define sa_handler   sa_u._sa_handler
    #define sa_sigaction sa_u._sa_sigaction
</PRE>

<H3>3.4.6 struct siginfo/siginfo_t</H3>

<P>
The following types is used to pass parameters to/from signal
handlers:
<PRE>
    typedef struct siginfo
    {
      int          si_signo;
      int          si_code;
      union sigval si_value;
   } siginfo_t;
</PRE>

<H3>3.4.7 union sigval</H3>

<P>
This defines the type of the struct siginfo si_value field and
is used to pass parameters with signals.
<PRE>
    union sigval
    {
      int   sival_int;
      void *sival_ptr;
    };
</PRE>

<H3>3.4.8 struct sigevent</H3>

<P>
The following is used to attach a signal to a message queue to
notify a task when a message is available on a queue.
<PRE>
    struct sigevent
    {
      int          sigev_signo;
      union sigval sigev_value;
      int          sigev_notify;
    };
</PRE>

<H3>3.4.9 Watchdog Data Types</H3>

<p>
  When a watchdog expires, the callback function with this
  type is called:
</p>
<pre>
    typedef void (*wdentry_t)(int argc, ...);
</pre>
<p>
  Where argc is the number of uint32 type arguments that follow.
</p>
  The arguments are passed as uint32 values.
  For systems where the sizeof(pointer) &lt; sizeof(uint32), the
  following union defines the alignment of the pointer within the
  uint32.  For example, the SDCC MCS51 general pointer is
  24-bits, but uint32 is 32-bits (of course).
</p>
<pre>
    union wdparm_u
    {
      void   *pvarg;
      uint32 *dwarg;
    };
    typedef union wdparm_u wdparm_t;
</pre>
<p>
  For most 32-bit systems, pointers and uint32 are the same size
  For systems where sizeof(pointer) > sizeof(uint32), we will
  have to do some redesign.
</p>

<h1><a name="FileSystem">2.10 Filesystem Interfaces</a></h1>
<p>
  The NuttX filesystem is very simple; it does not involve any block drivers or
  particular filesystem (like FAT or EXT2 etc.).
  The NuttX filesystem simply supports a set a filesystem APIs
  (<code>open()</code>, <code>close()</code>, <code>read()</code>, <code>write</code>, etc.)
  and a registration mechanism that allows devices drivers to a associated with <i>nodes</i>
  in a file-system-like name space.
</p>

<h2><a name="driveroperations">2.10.1 Driver Operations</a></h2>
<ul><pre>
  #include &lt;fcntl.h&gt;
  int open(const char *path, int oflag, ...);
</pre></ul>

<ul><pre>
  #include &lt;unistd.h&gt;
  int   close(int fd);
  int   dup(int fildes);
  int   dup2(int fildes1, int fildes2);
  off_t lseek(int fd, off_t offset, int whence);           /* Prototyped but not implemented */
  int   read(int fd, void *buf, unsigned int nbytes);
  int   unlink(const char *path);
  int   write(int fd, const void *buf, unsigned int nbytes);
</pre></ul>

<ul><pre>
  #include &lt;sys/ioctl.h&gt;
  int    ioctl(int fd, int req, unsigned long arg);
</pre></ul>

<h2><a name="directoryoperations">2.10.2 Directory Operations</a></h2>
<ul><pre>
  #include &lt;dirent.h&gt;
  int        closedir(DIR *dirp);
  FAR DIR   *opendir(const char *path);
  FAR struct dirent *readdir(FAR DIR *dirp);
  int        readdir_r(FAR DIR *dirp, FAR struct dirent *entry, FAR struct dirent **result);
  void       rewinddir(FAR DIR *dirp);
  void       seekdir(FAR DIR *dirp, int loc);
  int        telldir(FAR DIR *dirp);
</pre></ul>

<h2><a name="standardio">2.10.3 Standard I/O</a></h2>
<ul><pre>
  #include &lt;stdio.h&gt;
  int    fclose(FILE *stream);
  int    fflush(FILE *stream);
  int    feof(FILE *stream);                               /* Prototyped but not implemented */
  int    ferror(FILE *stream);                             /* Prototyped but not implemented */
  int    fgetc(FILE *stream);
  char  *fgets(char *s, int n, FILE *stream);
  FILE  *fopen(const char *path, const char *type);
  int    fprintf(FILE *stream, const char *format, ...);
  int    fputc(int c, FILE *stream);
  int    fputs(const char *s, FILE *stream);
  size_t fread(void *ptr, size_t size, size_t n_items, FILE *stream);
  int    fseek(FILE *stream, long int offset, int whence); /* Prototyped but not implemented */
  size_t fwrite(const void *ptr, size_t size, size_t n_items, FILE *stream);
  char  *gets(char *s);

  int    printf(const char *format, ...);
  int    puts(const char *s);
  int    rename(const char *source, const char *target);   /* Prototyped but not implemented */
  int    sprintf(char *dest, const char *format, ...);
  int    ungetc(int c, FILE *stream);
  int    vprintf(const char *s, va_list ap);
  int    vfprintf(FILE *stream, const char *s, va_list ap);
  int    vsprintf(char *buf, const char *s, va_list ap);

  int    chdir(const char *path);                          /* Prototyped but not implemented */
  FILE  *fdopen(int fd, const char *type);
  int    fstat(int fd, FAR struct stat *buf);              /* Prototyped but not implemented */
  char  *getcwd(FAR char *buf, size_t size);               /* Prototyped but not implemented */
  int    mkdir(const char *path, mode_t mode);             /* Prototyped but not implemented */
  int    rmdir(const char *path);                          /* Prototyped but not implemented */
  int    stat(const char *path, FAR struct stat *buf);     /* Prototyped but not implemented */
  int    statfs(const char *path, FAR struct statfs *buf); /* Prototyped but not implemented */
</pre></ul>

<h1><a name="index">Index</a></h1>
<ul>
  <li><a href="#clockgetres">clock_getres</a></li>
  <li><a href="#clockgettime">clock_gettime</a></li>
  <li><a href="#ClocksNTimers">Clocks</a></li>
  <li><a href="#clocksettime">clock_settime</a></li>
  <li><a href="#Data_Structures">Data structures</a></li>
  <li><a href="#directoryoperations">Directory operations</a></li>
  <li><a href="#driveroperations">Driver operations</a></li>
  <li><a href="#exit">exit</a></li>
  <li><a href="#FileSystem">Filesystem interfaces</a></li>
  <li><a href="#getpid">getpid</a></li>
  <li><a href="#gmtimer">gmtime_r</a></li>
  <li><a href="#Introduction">Introduction</a>
  <li><a href="#kill">kill</a></li>
  <li><a href="#localtimer">localtime_r</a></li>
  <li><a href="#Message_Queue">Named Message Queue Interfaces</a>
  <li><a href="#mktime">mktime</a></li>
  <li><a href="#mqclose">mq_close</a></li>
  <li><a href="#mqgetattr">mq_getattr</a></li>
  <li><a href="#mqnotify">mq_notify</a></li>
  <li><a href="#mqopen">mq_open</a></li>
  <li><a href="#mqreceive">mq_receive</a></li>
  <li><a href="#mqsend">mq_send</a></li>
  <li><a href="#mqsetattr">mq_setattr</a></li>
  <li><a href="#mqunlink">mq_unlink</a></li>
  <li><a href="#OS_Interfaces">OS Interfaces</a>
  <li><a href="#Pthread">Pthread Interfaces</a>
  <li><a href="#pthreadattrdestroy">pthread_attr_destroy</a></li>
  <li><a href="#pthreadattrgetinheritsched">pthread_attr_getinheritsched</a></li>
  <li><a href="#pthreadattrgetschedparam">pthread_attr_getschedparam</a></li>
  <li><a href="#pthreadattrgetschedpolicy">pthread_attr_getschedpolicy</a></li>
  <li><a href="#pthreadattrgetstacksize">0 pthread_attr_getstacksize</a></li>
  <li><a href="#pthreadattrinit">pthread_attr_init</a></li>
  <li><a href="#pthreadattrsetinheritsched">pthread_attr_setinheritsched</a></li>
  <li><a href="#pthreadattrsetschedparam">pthread_attr_setschedparam</a></li>
  <li><a href="#pthreadattrsetschedpolity">pthread_attr_setschedpolicy</a></li>
  <li><a href="#pthreadattrsetstacksize">pthread_attr_setstacksize</a></li>
  <li><a href="#pthreadbarrierattrinit">pthread_barrierattr_init</a></li>
  <li><a href="#pthreadbarrierattrdestroy">pthread_barrierattr_destroy</a></li>
  <li><a href="#pthreadbarrierattrgetpshared">pthread_barrierattr_getpshared</a></li>
  <li><a href="#pthreadbarrierattrsetpshared">pthread_barrierattr_setpshared</a></li>
  <li><a href="#pthreadbarrierdestroy">pthread_barrier_destroy</a></li>
  <li><a href="#pthreadbarrierinit">pthread_barrier_init</a></li>
  <li><a href="#pthreadbarrierwait">pthread_barrier_wait</a></li>
  <li><a href="#pthreadcancel">pthread_cancel</a></li>
  <li><a href="#pthreadconaddrinit">pthread_condattr_init</a></li>
  <li><a href="#pthreadcondbroadcast">pthread_cond_broadcast</a></li>
  <li><a href="#pthreadconddestroy">pthread_cond_destroy</a></li>
  <li><a href="#pthreadcondinit">pthread_cond_init</a></li>
  <li><a href="#pthreadcondsignal">pthread_cond_signal</a></li>
  <li><a href="#pthreadcondtimedwait">pthread_cond_timedwait</a></li>
  <li><a href="#pthreadcondwait">pthread_cond_wait</a></li>
  <li><a href="#pthreadcreate">pthread_create</a></li>
  <li><a href="#pthreaddetach">pthread_detach</a></li>
  <li><a href="#pthreadexit">pthread_exit</a></li>
  <li><a href="#pthreadgetschedparam">pthread_getschedparam</a></li>
  <li><a href="#pthreadgetspecific">pthread_getspecific</a></li>
  <li><a href="#Pthread"><i>pthreads</i></a> share some resources.
  <li><a href="#pthreadjoin">pthread_join</a></li>
  <li><a href="#pthreadkeycreate">pthread_key_create</a></li>
  <li><a href="#pthreadkeydelete">pthread_key_delete</a></li>
  <li><a href="#pthreadkill">pthread_kill</a></li>
  <li><a href="#pthreadmutexattrdestroy">pthread_mutexattr_destroy</a></li>
  <li><a href="#pthreadmutexattrgetpshared">pthread_mutexattr_getpshared</a></li>
  <li><a href="#pthreadmutexattrinit">pthread_mutexattr_init</a></li>
  <li><a href="#pthreadmutexattrsetpshared">pthread_mutexattr_setpshared</a></li>
  <li><a href="#pthreadmutexdestrory">pthread_mutex_destroy</a></li>
  <li><a href="#pthreadmutexinit">pthread_mutex_init</a></li>
  <li><a href="#pthreadmutexlock">pthread_mutex_lock</a></li>
  <li><a href="#pthreadmutextrylock">pthread_mutex_trylock</a></li>
  <li><a href="#pthreadmutexunlock">pthread_mutex_unlock</a></li>
  <li><a href="#pthreadocndattrdestroy">pthread_condattr_destroy</a></li>
  <li><a href="#pthreadonce">pthread_once</a></li>
  <li><a href="#pthreadself">pthread_self</a></li>
  <li><a href="#pthreadsetcancelstate">pthread_setcancelstate</a></li>
  <li><a href="#pthreadsetschedparam">pthread_setschedparam</a></li>
  <li><a href="#pthreadsetspecific">pthread_setspecific</a></li>
  <li><a href="#pthreadsigmask">pthread_sigmask</a></li>
  <li><a href="#pthreadtestcancelstate">pthread_testcancelstate</a></li>
  <li><a href="#pthreadyield">pthread_yield</a></li>
  <li><a href="#schedgetparam">sched_getparam</a></li>
  <li><a href="#schedgetprioritymax">sched_get_priority_max</a></li>
  <li><a href="#schedgetprioritymin">sched_get_priority_min</a></li>
  <li><a href="#schedgetrrinterval">sched_get_rr_interval</a></li>
  <li><a href="#schedlockcount">sched_lockcount</a></li>
  <li><a href="#schedlock">sched_lock</a></li>
  <li><a href="#schedsetparam">sched_setparam</a></li>
  <li><a href="#schedsetscheduler">sched_setscheduler</a></li>
  <li><a href="#schedunlock">sched_unlock</a></li>
  <li><a href="#sched_yield">sched_yield</a></li>
  <li><a href="#Semaphores">Counting Semaphore Interfaces</a>
  <li><a href="#semclose">sem_close</a></li>
  <li><a href="#semdestroy">sem_destroy</a></li>
  <li><a href="#semgetvalue">sem_getvalue</a></li>
  <li><a href="#seminit">sem_init</a></li>
  <li><a href="#semopen">sem_open</a></li>
  <li><a href="#sempost">sem_post</a></li>
  <li><a href="#semtrywait">sem_trywait</a></li>
  <li><a href="#semunlink">sem_unlink</a></li>
  <li><a href="#semwait">sem_wait</a></li>
  <li><a href="#setgetscheduler">sched_getscheduler</a></li>
  <li><a href="#sigaction">sigaction</a></li>
  <li><a href="#sigaddset">sigaddset</a></li>
  <li><a href="#sigdelset">sigdelset</a></li>
  <li><a href="#sigemptyset">sigemptyset</a></li>
  <li><a href="#sigfillset">sigfillset</a></li>
  <li><a href="#sigismember">sigismember</a></li>
  <li><a href="#Signals">Signal Interfaces</a>
  <li><a href="#sigpending">sigpending</a></li>
  <li><a href="#sigprocmask">sigprocmask</a></li>
  <li><a href="#sigqueue">sigqueue</a></li>
  <li><a href="#sigsuspend">sigsuspend</a></li>
  <li><a href="#sigtimedwait">sigtimedwait</a></li>
  <li><a href="#sigwaitinfo">sigwaitinfo</a></li>
  <li><a href="#standardio">Standard I/O</a></li>
  <li><a href="#taskactivate">task_activate</a></li>
  <li><a href="#Task_Control">Task Control Interfaces</a>
  <li><a href="#taskcreate">task_create</a></li>
  <li><a href="#taskdelete">task_delete</a></li>
  <li><a href="#taskinit">task_init</a></li>
  <li><a href="#taskrestart">task_restart</a></li>
  <li><a href="#Task_Schedule">Task Scheduling Interfaces</a>
  <li><a href="#Task_Switch">Task Switching Interfaces</a>
  <li><a href="#timercreate">timer_create</a></li>
  <li><a href="#timerdelete">timer_delete</a></li>
  <li><a href="#timergetoverrun">timer_getoverrun</a></li>
  <li><a href="#timergettime">timer_gettime</a></li>
  <li><a href="#ClocksNTimers">Timers</a></li>
  <li><a href="#timersettime">timer_settime</a></li>
  <li><a href="#Watchdogs">Watchdog Timer Interfaces</a>
  <li><a href="#wdcancel">wd_cancel</a></li>
  <li><a href="#wdcreate">wd_create</a></li>
  <li><a href="#wddelete">wd_delete</a></li>
  <li><a href="#wdgettime">wd_gettime</a></li>
  <li><a href="#wdstart">wd_start</a></li>
</ul>

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