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   <section id="symmetric-multiprocessing-smp-application">
 <h1>Symmetric Multiprocessing (SMP) Application<a class="headerlink" href="#symmetric-multiprocessing-smp-application" title="Permalink to this heading"></a></h1>
 <p>According to Wikipedia: “Symmetric multiprocessing (SMP) involves
 a symmetric multiprocessor system hardware and software
 architecture where two or more identical processors connect to a
 single, shared main memory, have full access to all I/O devices,
 and are controlled by a single operating system instance that
 treats all processors equally, reserving none for special
 purposes. Most multiprocessor systems today use an SMP
 architecture. In the case of multi-core processors, the SMP
 architecture applies to the cores, treating them as separate
 processors.</p>
 <p>“SMP systems are tightly coupled multiprocessor systems with a
 pool of homogeneous processors running independently, each
 processor executing different programs and working on different
 data and with capability of sharing common resources (memory, I/O
 device, interrupt system and so on) and connected using a system
 bus or a crossbar.”</p>
 <p>For a technical description of the NuttX implementation of SMP,
 see the NuttX <a class="reference external" href="https://cwiki.apache.org/confluence/display/NUTTX/SMP">SMP Wiki
 Page</a>.</p>
 <dl class="c function">
 <dt class="sig sig-object c" id="c.up_testset">
 <span class="n"><span class="pre">spinlock_t</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_testset</span></span></span><span class="sig-paren">(</span><span class="pre">FAR</span><span class="w"> </span><span class="k"><span class="pre">volatile</span></span><span class="w"> </span><span class="n"><span class="pre">spinlock_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">lock</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_testset" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Perform and atomic test and set operation on the provided spinlock.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Parameters<span class="colon">:</span></dt>
 <dd class="field-odd"><ul class="simple">
 <li><p><strong>lock</strong> – The address of spinlock object.</p></li>
 </ul>
 </dd>
 <dt class="field-even">Returns<span class="colon">:</span></dt>
 <dd class="field-even"><p>The spinlock is always locked upon return. The value
 of previous value of the spinlock variable is returned,
 either SP_LOCKED if the spinlock was previously locked
 (meaning that the test-and-set operation failed to obtain the lock)
 or SP_UNLOCKED if the spinlock was previously unlocked
 (meaning that we successfully obtained the lock)</p>
 </dd>
 </dl>
 </dd></dl>

 <dl class="c function">
 <dt class="sig sig-object c" id="c.up_cpu_index">
 <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_cpu_index</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_cpu_index" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Return an index in the range of 0 through (CONFIG_SMP_NCPUS-1)
 that corresponds to the currently executing CPU.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Returns<span class="colon">:</span></dt>
 <dd class="field-odd"><p>An integer index in the range of 0 through
 (CONFIG_SMP_NCPUS-1) that corresponds to the
 currently executing CPU.</p>
 </dd>
 </dl>
 </dd></dl>

 <dl class="c function">
 <dt class="sig sig-object c" id="c.up_cpu_start">
 <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_cpu_start</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">cpu</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_cpu_start" title="Permalink to this definition"></a><br /></dt>
 <dd><p>In an SMP configuration, only one CPU is initially active (CPU 0).
 System initialization occurs on that single thread. At the
 completion of the initialization of the OS, just before
 beginning normal multitasking, the additional CPUs would
 be started by calling this function.</p>
 <p>Each CPU is provided the entry point to is IDLE task when started.
 A TCB for each CPU’s IDLE task has been initialized and
 placed in the CPU’s g_assignedtasks[cpu] list. A stack
 has also been allocated and initialized.</p>
 <p>The OS initialization logic calls this function repeatedly until
 each CPU has been started, 1 through (CONFIG_SMP_NCPUS-1).</p>
 <dl class="field-list simple">
 <dt class="field-odd">Parameters<span class="colon">:</span></dt>
 <dd class="field-odd"><ul class="simple">
 <li><p><strong>cpu</strong> – The index of the CPU being started. This will be a
 numeric value in the range of from one to
 <code class="docutils literal notranslate"><span class="pre">(CONFIG_SMP_NCPUS-1)</span></code>). (CPU 0 is already active).</p></li>
 </ul>
 </dd>
 <dt class="field-even">Returns<span class="colon">:</span></dt>
 <dd class="field-even"><p>Zero (OK) is returned on success; a negated errno value on failure.</p>
 </dd>
 </dl>
 </dd></dl>

 <dl class="c function">
 <dt class="sig sig-object c" id="c.up_cpu_pause">
 <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_cpu_pause</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">cpu</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_cpu_pause" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Save the state of the current task at the head of the
 <code class="docutils literal notranslate"><span class="pre">g_assignedtasks[cpu]</span></code> task list and then pause task execution on the CPU.</p>
 <p>This function is called by the OS when the logic executing on
 one CPU needs to modify the state of the <code class="docutils literal notranslate"><span class="pre">g_assignedtasks[cpu]</span></code>
 list for another CPU.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Parameters<span class="colon">:</span></dt>
 <dd class="field-odd"><ul class="simple">
 <li><p><strong>cpu</strong> – The index of the CPU to be paused. This will not be
 the index of the currently executing CPU.</p></li>
 </ul>
 </dd>
 <dt class="field-even">Returns<span class="colon">:</span></dt>
 <dd class="field-even"><p>Zero (OK) is returned on success; a negated errno value on failure.</p>
 </dd>
 </dl>
 </dd></dl>

 <dl class="c function">
 <dt class="sig sig-object c" id="c.up_cpu_resume">
 <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_cpu_resume</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">cpu</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_cpu_resume" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Restart the cpu after it was paused via up_cpu_pause(),
 restoring the state of the task at the head of the
 <code class="docutils literal notranslate"><span class="pre">g_assignedtasks[cpu]</span></code> list, and resume normal tasking.</p>
 <p>This function is called after <code class="docutils literal notranslate"><span class="pre">up_cpu_pause()</span></code> in order
 resume operation of the CPU after modifying its
 <code class="docutils literal notranslate"><span class="pre">g_assignedtasks[cpu]</span></code> list.</p>
 <dl class="field-list simple">
 <dt class="field-odd">Parameters<span class="colon">:</span></dt>
 <dd class="field-odd"><ul class="simple">
 <li><p><strong>cpu</strong> – The index of the CPU being resumed. This will not be
 the index of the currently executing CPU.</p></li>
 </ul>
 </dd>
 <dt class="field-even">Returns<span class="colon">:</span></dt>
 <dd class="field-even"><p>Zero (OK) is returned on success; a negated errno value on failure.</p>
 </dd>
 </dl>
 </dd></dl>

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	<section id="symmetric-multiprocessing-smp-application">
	<h1>Symmetric Multiprocessing (SMP) Application<a class="headerlink" href="#symmetric-multiprocessing-smp-application" title="Permalink to this heading"></a></h1>
	<p>According to Wikipedia: “Symmetric multiprocessing (SMP) involves
	a symmetric multiprocessor system hardware and software
	architecture where two or more identical processors connect to a
	single, shared main memory, have full access to all I/O devices,
	and are controlled by a single operating system instance that
	treats all processors equally, reserving none for special
	purposes. Most multiprocessor systems today use an SMP
	architecture. In the case of multi-core processors, the SMP
	architecture applies to the cores, treating them as separate
	processors.</p>
	<p>“SMP systems are tightly coupled multiprocessor systems with a
	pool of homogeneous processors running independently, each
	processor executing different programs and working on different
	data and with capability of sharing common resources (memory, I/O
	device, interrupt system and so on) and connected using a system
	bus or a crossbar.”</p>
	<p>For a technical description of the NuttX implementation of SMP,
	see the NuttX <a class="reference external" href="https://cwiki.apache.org/confluence/display/NUTTX/SMP">SMP Wiki
	Page</a>.</p>
	<dl class="c function">
	<dt class="sig sig-object c" id="c.up_testset">
	<span class="n"><span class="pre">spinlock_t</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_testset</span></span></span><span class="sig-paren">(</span><span class="pre">FAR</span><span class="w"> </span><span class="k"><span class="pre">volatile</span></span><span class="w"> </span><span class="n"><span class="pre">spinlock_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">lock</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_testset" title="Permalink to this definition"></a><br /></dt>
	<dd><p>Perform and atomic test and set operation on the provided spinlock.</p>
	<dl class="field-list simple">
	<dt class="field-odd">Parameters<span class="colon">:</span></dt>
	<dd class="field-odd"><ul class="simple">
	<li><p><strong>lock</strong> – The address of spinlock object.</p></li>
	</ul>
	</dd>
	<dt class="field-even">Returns<span class="colon">:</span></dt>
	<dd class="field-even"><p>The spinlock is always locked upon return. The value
	of previous value of the spinlock variable is returned,
	either SP_LOCKED if the spinlock was previously locked
	(meaning that the test-and-set operation failed to obtain the lock)
	or SP_UNLOCKED if the spinlock was previously unlocked
	(meaning that we successfully obtained the lock)</p>
	</dd>
	</dl>
	</dd></dl>

	<dl class="c function">
	<dt class="sig sig-object c" id="c.up_cpu_index">
	<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_cpu_index</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_cpu_index" title="Permalink to this definition"></a><br /></dt>
	<dd><p>Return an index in the range of 0 through (CONFIG_SMP_NCPUS-1)
	that corresponds to the currently executing CPU.</p>
	<dl class="field-list simple">
	<dt class="field-odd">Returns<span class="colon">:</span></dt>
	<dd class="field-odd"><p>An integer index in the range of 0 through
	(CONFIG_SMP_NCPUS-1) that corresponds to the
	currently executing CPU.</p>
	</dd>
	</dl>
	</dd></dl>

	<dl class="c function">
	<dt class="sig sig-object c" id="c.up_cpu_start">
	<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_cpu_start</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">cpu</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_cpu_start" title="Permalink to this definition"></a><br /></dt>
	<dd><p>In an SMP configuration, only one CPU is initially active (CPU 0).
	System initialization occurs on that single thread. At the
	completion of the initialization of the OS, just before
	beginning normal multitasking, the additional CPUs would
	be started by calling this function.</p>
	<p>Each CPU is provided the entry point to is IDLE task when started.
	A TCB for each CPU’s IDLE task has been initialized and
	placed in the CPU’s g_assignedtasks[cpu] list. A stack
	has also been allocated and initialized.</p>
	<p>The OS initialization logic calls this function repeatedly until
	each CPU has been started, 1 through (CONFIG_SMP_NCPUS-1).</p>
	<dl class="field-list simple">
	<dt class="field-odd">Parameters<span class="colon">:</span></dt>
	<dd class="field-odd"><ul class="simple">
	<li><p><strong>cpu</strong> – The index of the CPU being started. This will be a
	numeric value in the range of from one to
	<code class="docutils literal notranslate"><span class="pre">(CONFIG_SMP_NCPUS-1)</span></code>). (CPU 0 is already active).</p></li>
	</ul>
	</dd>
	<dt class="field-even">Returns<span class="colon">:</span></dt>
	<dd class="field-even"><p>Zero (OK) is returned on success; a negated errno value on failure.</p>
	</dd>
	</dl>
	</dd></dl>

	<dl class="c function">
	<dt class="sig sig-object c" id="c.up_cpu_pause">
	<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_cpu_pause</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">cpu</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_cpu_pause" title="Permalink to this definition"></a><br /></dt>
	<dd><p>Save the state of the current task at the head of the
	<code class="docutils literal notranslate"><span class="pre">g_assignedtasks[cpu]</span></code> task list and then pause task execution on the CPU.</p>
	<p>This function is called by the OS when the logic executing on
	one CPU needs to modify the state of the <code class="docutils literal notranslate"><span class="pre">g_assignedtasks[cpu]</span></code>
	list for another CPU.</p>
	<dl class="field-list simple">
	<dt class="field-odd">Parameters<span class="colon">:</span></dt>
	<dd class="field-odd"><ul class="simple">
	<li><p><strong>cpu</strong> – The index of the CPU to be paused. This will not be
	the index of the currently executing CPU.</p></li>
	</ul>
	</dd>
	<dt class="field-even">Returns<span class="colon">:</span></dt>
	<dd class="field-even"><p>Zero (OK) is returned on success; a negated errno value on failure.</p>
	</dd>
	</dl>
	</dd></dl>

	<dl class="c function">
	<dt class="sig sig-object c" id="c.up_cpu_resume">
	<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_cpu_resume</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">cpu</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_cpu_resume" title="Permalink to this definition"></a><br /></dt>
	<dd><p>Restart the cpu after it was paused via up_cpu_pause(),
	restoring the state of the task at the head of the
	<code class="docutils literal notranslate"><span class="pre">g_assignedtasks[cpu]</span></code> list, and resume normal tasking.</p>
	<p>This function is called after <code class="docutils literal notranslate"><span class="pre">up_cpu_pause()</span></code> in order
	resume operation of the CPU after modifying its
	<code class="docutils literal notranslate"><span class="pre">g_assignedtasks[cpu]</span></code> list.</p>
	<dl class="field-list simple">
	<dt class="field-odd">Parameters<span class="colon">:</span></dt>
	<dd class="field-odd"><ul class="simple">
	<li><p><strong>cpu</strong> – The index of the CPU being resumed. This will not be
	the index of the currently executing CPU.</p></li>
	</ul>
	</dd>
	<dt class="field-even">Returns<span class="colon">:</span></dt>
	<dd class="field-even"><p>Zero (OK) is returned on success; a negated errno value on failure.</p>
	</dd>
	</dl>
	</dd></dl>

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