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</p>
<h3><a name="listmgmt">4.2.2 OS List Management APIs</a></h3></h3>
<p>
<b><i>To be provided</i></b>
</p>
<h3><a name="schedprocesstimer">4.2.3 <code>sched_process_timer()</code></a></h3>
<p><b>Prototype</b>: <code>void sched_process_timer(void);</code></p>
<p><b>Description</b>.
This function handles system timer events.
The timer interrupt logic itself is implemented in the
architecture specific code, but must call the following OS
function periodically -- the calling interval must be
<code>MSEC_PER_TICK</code>.
</p>
<h3><a name="irqdispatch">4.2.4 <code>irq_dispatch()</code></a></h3>
<p><b>Prototype</b>: <code>void irq_dispatch(int irq, FAR void *context);</code></p>
<p><b>Description</b>.
This function must be called from the achitecture-
specific logic in order to dispaly an interrupt to
the appropriate, registered handling logic.
</p>
<h1><a name="apndxconfigs">Appendix A: NuttX Configuration Settings</a></h1>
<p>
The following variables are recognized by the build (you may
also include architecture-specific settings).
</p>
<h2>Architecture selection</h2>
<ul>
<li><code>CONFIG_ARCH</code>: identifies the arch subdirectory
<li><code>CONFIG_ARCH_name</code>: for use in C code
</ul>
<h2>General OS setup</h2>
<ul>
<li>
<code>CONFIG_EXAMPLE</code>: identifies the subdirectory in examples
that will be used in the build.
</li>
<li>
<code>CONFIG_DEBUG</code>: enables built-in debug options
</li>
<li>
<code>CONFIG_DEBUG_VERBOSE</code>: enables verbose debug output
</li>
<li>
<code>CONFIG_HAVE_LOWPUTC</code>: architecture supports low-level, boot
time console output
</li>
<li>
<code>CONFIG_MM_REGIONS</code>: If the architecture includes multiple
regions of memory to allocate from, this specifies the
number of memory regions that the memory manager must
handle and enables the API mm_addregion(start, end);
</li>
<li>
<code>CONFIG_RR_INTERVAL</code>: The round robin timeslice will be set
this number of milliseconds; Round robin scheduling can
be disabled by setting this value to zero.
</li>
<li>
<code>CONFIG_SCHED_INSTRUMENTATION</code>: enables instrumentation in
scheduler to monitor system performance
</li>
<li>
<code>CONFIG_TASK_NAME_SIZE</code>: Spcifies that maximum size of a
task name to save in the TCB. Useful if scheduler
instrumentation is selected. Set to zero to disable.
</li>
<li>
<code>CONFIG_START_YEAR, CONFIG_START_MONTH, CONFIG_START_DAY -
Used to initialize the internal time logic.
</li>
<li>
<code>CONFIG_JULIAN_TIME</code>: Enables Julian time conversions
</li>
<li>
<code>CONFIG_DEV_CONSOLE</code>: Set if architecture-specific logic
provides /dev/console. Enables stdout, stderr, stdin.
</li>
</ul>
<p>
The following can be used to disable categories of APIs supported
by the OS. If the compiler supports weak functions, then it
should not be necessary to disable functions unless you want to
restrict usage of those APIs.
</p>
<p>
There are certain dependency relationships in these features.
</p>
<ul>
<li>
<code>mq_notify()</code> logic depends on signals to awaken tasks
waiting for queues to become full or empty.
</li>
<li>
<code>pthread_condtimedwait()</code> depends on signals to wake
up waiting tasks.
</li>
</ul>
<ul>
<code>CONFIG_DISABLE_CLOCK</code>, <code>CONFI_DISABLE_POSIX_TIMERS</code>, <code>CONFIG_DISABLE_PTHREAD</code>,
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<code>CONFIG_DISABLE_SIGNALS</code>, <code>CONFIG_DISABLE_MQUEUE</code>,
</ul>
<h2>Miscellaneous libc settings</h2>
<ul>
<li>
<code>CONFIG_NOPRINTF_FIELDWIDTH</code>: sprintf-related logic is a
little smaller if we do not support fieldwidthes
</li>
</ul>
<h2>Allow for architecture optimized implementations</h2>
<p>
The architecture can provide optimized versions of the
following to improve sysem performance.
</p>
<ul>
<p>
<code>CONFIG_ARCH_MEMCPY</code>, <code>CONFIG_ARCH_MEMCMP</code>, <code>CONFIG_ARCH_MEMMOVE</code>,
<code>CONFIG_ARCH_MEMSET</code>, <code>CONFIG_ARCH_STRCMP</code>, <code>CONFIG_ARCH_STRCPY</code>,
<code>CONFIG_ARCH_STRNCPY</code>, <code>CONFIG_ARCH_STRLEN</code>, <code>CONFIG_ARCH_BZERO</code>,
<code>CONFIG_ARCH_KMALLOC</code>, <code>CONFIG_ARCH_KZMALLOC</code>, <code>ONFIG_ARCH_KFREE</code>,
</p>
</ul>
<h2>Sizes of configurable things (0 disables)</h2>
<ul>
<li>
<code>CONFIG_MAX_TASKS</code>: The maximum number of simultaneously
active tasks. This value must be a power of two.
</li>
<li>
<code>CONFIG_NPTHREAD_KEYS</code>: The number of items of thread-
specific data that can be retained
</li>
<li>
<code>CONFIG_NFILE_DESCRIPTORS</code>: The maximum number of file
descriptors (one for each open)
</li>
<li>
<code>CONFIG_NFILE_STREAMS</code>: The maximum number of streams that
can be fopen'ed
</li>
<li>
<code>CONFIG_NAME_MAX</code>: The maximum size of a file name.
</li>
<li>
<code>CONFIG_STDIO_BUFFER_SIZE</code>: Size of the buffer to allocate
on fopen. (Only if CONFIG_NFILE_STREAMS > 0)
</li>
<li>
<code>CONFIG_NUNGET_CHARS</code>: Number of characters that can be
buffered by ungetc() (Only if CONFIG_NFILE_STREAMS > 0)
</li>
<li>
<code>CONFIG_PREALLOC_MQ_MSGS</code>: The number of pre-allocated message
structures. The system manages a pool of preallocated
message structures to minimize dynamic allocations
</li>
<li>
<code>CONFIG_MQ_MAXMSGSIZE</code>: Message structures are allocated with
a fixed payload size given by this settin (does not include
other message structure overhead.
</li>
<li>
<code>CONFIG_PREALLOC_WDOGS</code>: The number of pre-allocated watchdog
structures. The system manages a pool of preallocated
watchdog structures to minimize dynamic allocations
</li>
</ul>
<h2>Stack and heap information</h2>
<ul>
<li>
<code>CONFIG_BOOT_FROM_FLASH</code>: Some configurations support XIP
operation from FLASH.
</li>
<li>
<code>CONFIG_STACK_POINTER</code>: The initial stack pointer
</li>
<li>
<code>CONFIG_PROC_STACK_SIZE</code>: The size of the initial stack
</li>
<li>
<code>CONFIG_PTHREAD_STACK_MIN</code>: Minimum pthread stack size
</li>
<li>
<code>CONFIG_PTHREAD_STACK_DEFAULT</code>: Default pthread stack size
</li>
<li>
<code>CONFIG_HEAP_BASE</code>: The beginning of the heap
</li>
<li>
<code>CONFIG_HEAP_SIZE</code>: The size of the heap
</li>
</ul>