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<title>NuttX Users Manual</title>
<meta name="AUTHOR" content="Gregory Nutt">
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<h1><big><font color="#3c34ec"><i>NuttX Operating System<p>User's Manual</i></font></big></h1>
<p><small>by</small></p>
<p>Gregory Nutt<p>
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<a name="Introduction"><h1>1.0 Introduction</h1></a>
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<p>
This manual provides general usage information for the NuttX RTOS from the
perspective of the firmware developer.
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<a name="overview"><h2>1.1 Document Overview</h2></a>
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<p>
This user's manual is divided into three sections plus a index:
</p>
<ul>
<li>
<b>Section 1.0, <a href="#Introduction">Introduction</a></b>:
This section provides an overview of the NuttX user's manual.
</li>
<li>
<b>Section 2.0, <a href="#OS_Interfaces">OS Interfaces</a></b>:
This section details the program interfaces provided by NuttX.
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>
<li>Paragraph 2.2 <a href="#Task_Schedule">Task Scheduling Interfaces</a></li>
<li>Paragraph 2.3 <a href="#Task_Switch">Task Switching Interfaces</a></li>
<li>Paragraph 2.4 <a href="#Message_Queue">Named Message Queue Interfaces</a></li>
<li>Paragraph 2.5 <a href="#Semaphores">Counting Semaphore Interfaces</a></li>
<li>Paragraph 2.6 <a href="#Watchdogs">Watchdog Timer Interfaces</a></li>
<li>Paragraph 2.7 <a href="#ClocksNTimers">Clocks and Timers</a></li>
<li>Paragraph 2.8 <a href="#Signals">Signal Interfaces</a></li>
<li>Paragraph 2.9 <a href="#Pthread">Pthread Interfaces</a></li>
<li>Paragraph 2.10 <a href="#Environ">Environment Variables</a></li>
<li>Paragraph 2.11 <a href="#FileSystem">File System Interfaces</a></li>
<li>Paragraph 2.12 <a href="#Network">Network Interfaces</a></li>
</ul>
</li>
<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.
<ul>
<li>Paragraph 3.1 <a href="#ScalarType">Scalar Types</a></li>
<li>Paragraph 3.2 <a href="#HiddenStructures">Hidden Interface Structures</a></li>
<li>Paragraph 3.3 <a href="#ErrnoAccess">Access to the <code>errno</code> Variable</a></li>
<li>Paragraph 3.4 <a href="#UserStructures">User Interface Structures</a></li>
</ul>
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<a name="scope"><h2>1.2 Intended Audience and Scope</h2></a>
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<p>
The intended audience for this document are firmware developers who are implementing applications on NuttX.
Specifically, this documented is limited to addressing only NuttX RTOS APIs that are available to the application developer.
As such, this document does not focus on any technical details of the organization or implementation of NuttX.
Those technical details are provided in the <a href="NuttxPortingGuide.html">NuttX Porting Guide</a>.
</p>
<p>
Information about configuring and building NuttX is also needed by the application developer.
That information can also be found in the <a href="NuttxPortingGuide.html#configandbuild">NuttX Porting Guide</a>.
</p>
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<a name="OS_Interfaces"><h1>2.0 OS Interfaces</h1></a>
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<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
<p>
<b>Description:</b> The operation performed by the interface function
<p>
<b>Input Parameters:</b> All input parameters are listed along
<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
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.
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<a name="Task_Control"><h2>2.1 Task Control Interfaces</h2></a>
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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>:
<li><i>tasks</i> are threads which have a degree of independence
<li><a href="#Pthread"><i>pthreads</i></a> share some resources.
<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 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>
<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>
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