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   <section id="apis-exported-by-board-specific-logic-to-nuttx">
 <h1>APIs Exported by Board-Specific Logic to NuttX<a class="headerlink" href="#apis-exported-by-board-specific-logic-to-nuttx" title="Permalink to this heading"></a></h1>
 <p>Exported board-specific interfaces are prototyped in the header
 file <code class="docutils literal notranslate"><span class="pre">include/nuttx/board.h</span></code>. There are many interfaces exported
 from board- to architecture-specific logic. But there are only a
 few exported from board-specific logic to common NuttX logic.
 Those few of those related to initialization will be discussed in
 this paragraph. There are others, like those used by
 <code class="docutils literal notranslate"><span class="pre">`boardctl()</span></code> &lt;#boardctl&gt;`__ that will be discussed in other
 paragraphs.</p>
 <p>All of the board-specific interfaces used by the NuttX OS logic
 are for controlled board initialization. There are three points in
 time where you can insert custom, board-specific initialization
 logic:</p>
 <p>First, <code class="docutils literal notranslate"><span class="pre">&lt;arch&gt;_board_initialize()</span></code>: This function is <em>not</em>
 called from the common OS logic, but rather from the
 architecture-specific power on reset logic. This is used only for
 initialization of very low-level things like configuration of GPIO
 pins, power settings, DRAM initialization, etc. The OS has not
 been initialized at this point, so you cannot allocate memory or
 initialize device drivers.</p>
 <p>The other two board initialization <em>hooks</em> are called from the OS
 start-up logic and are described in the following paragraphs:</p>
 <dl class="c function">
 <dt class="sig sig-object c" id="c.board_early_initialize">
 <span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">board_early_initialize</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.board_early_initialize" title="Permalink to this definition"></a><br /></dt>
 <dd><p>The next level of initialization is performed by a call to
 <code class="docutils literal notranslate"><span class="pre">up_initialize()</span></code> (in
 <code class="docutils literal notranslate"><span class="pre">arch/&lt;arch&gt;/src/common/up_initialize.c</span></code>). The OS has been
 initialized at this point and it is okay to initialize drivers in
 this phase. <code class="docutils literal notranslate"><span class="pre">up_initialize()</span></code> is <em>not</em> a board-specific
 interface, but rather an architecture-specific, board-independent
 interface.</p>
 <p>But at this same point in time, the OS will also call a
 board-specific initialization function named
 <code class="docutils literal notranslate"><span class="pre">board_early_initialize()</span></code> if
 <code class="docutils literal notranslate"><span class="pre">CONFIG_BOARD_EARLY_INITIALIZE=y</span></code> is selected in the
 configuration. The context in which <code class="docutils literal notranslate"><span class="pre">board_early_initialize()</span></code>
 executes is suitable for early initialization of most, simple
 device drivers and is a logical, board-specific extension of
 up_initialize().</p>
 <p><code class="docutils literal notranslate"><span class="pre">board_early_initialize()</span></code> runs on the startup, initialization
 thread. Some initialization operations cannot be performed on the
 start-up, initialization thread. That is because the
 initialization thread cannot wait for event. Waiting may be
 required, for example, to mount a file system or or initialize a
 device such as an SD card. For this reason, such driver initialize
 must be deferred to <code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code>.</p>
 </dd></dl>

 <dl class="c function">
 <dt class="sig sig-object c" id="c.board_late_initialize">
 <span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">board_late_initialize</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.board_late_initialize" title="Permalink to this definition"></a><br /></dt>
 <dd><p>And, finally, just before the user application code starts. If
 <code class="docutils literal notranslate"><span class="pre">CONFIG_BOARD_LATE_INITIALIZE=y</span></code> is selected in the
 configuration, then an final, additional initialization call will
 be performed in the boot-up sequence to a function called
 <code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code>. <code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code> will be
 called well after <code class="docutils literal notranslate"><span class="pre">up_initialize()</span></code> and
 <code class="docutils literal notranslate"><span class="pre">board_early_initialize()</span></code> are called.
 <code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code> will be called just before the main
 application task is started. This additional initialization phase
 may be used, for example, to initialize more complex,
 board-specific device drivers.</p>
 <p>Waiting for events, use of I2C, SPI, etc are permissible in the
 context of board_late_initialize(). That is because
 <code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code> will run on a temporary, internal
 kernel thread.</p>
 </dd></dl>

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	<section id="apis-exported-by-board-specific-logic-to-nuttx">
	<h1>APIs Exported by Board-Specific Logic to NuttX<a class="headerlink" href="#apis-exported-by-board-specific-logic-to-nuttx" title="Permalink to this heading"></a></h1>
	<p>Exported board-specific interfaces are prototyped in the header
	file <code class="docutils literal notranslate"><span class="pre">include/nuttx/board.h</span></code>. There are many interfaces exported
	from board- to architecture-specific logic. But there are only a
	few exported from board-specific logic to common NuttX logic.
	Those few of those related to initialization will be discussed in
	this paragraph. There are others, like those used by
	<code class="docutils literal notranslate"><span class="pre">`boardctl()</span></code> <#boardctl>`__ that will be discussed in other
	paragraphs.</p>
	<p>All of the board-specific interfaces used by the NuttX OS logic
	are for controlled board initialization. There are three points in
	time where you can insert custom, board-specific initialization
	logic:</p>
	<p>First, <code class="docutils literal notranslate"><span class="pre"><arch>_board_initialize()</span></code>: This function is <em>not</em>
	called from the common OS logic, but rather from the
	architecture-specific power on reset logic. This is used only for
	initialization of very low-level things like configuration of GPIO
	pins, power settings, DRAM initialization, etc. The OS has not
	been initialized at this point, so you cannot allocate memory or
	initialize device drivers.</p>
	<p>The other two board initialization <em>hooks</em> are called from the OS
	start-up logic and are described in the following paragraphs:</p>
	<dl class="c function">
	<dt class="sig sig-object c" id="c.board_early_initialize">
	<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">board_early_initialize</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.board_early_initialize" title="Permalink to this definition"></a><br /></dt>
	<dd><p>The next level of initialization is performed by a call to
	<code class="docutils literal notranslate"><span class="pre">up_initialize()</span></code> (in
	<code class="docutils literal notranslate"><span class="pre">arch/<arch>/src/common/up_initialize.c</span></code>). The OS has been
	initialized at this point and it is okay to initialize drivers in
	this phase. <code class="docutils literal notranslate"><span class="pre">up_initialize()</span></code> is <em>not</em> a board-specific
	interface, but rather an architecture-specific, board-independent
	interface.</p>
	<p>But at this same point in time, the OS will also call a
	board-specific initialization function named
	<code class="docutils literal notranslate"><span class="pre">board_early_initialize()</span></code> if
	<code class="docutils literal notranslate"><span class="pre">CONFIG_BOARD_EARLY_INITIALIZE=y</span></code> is selected in the
	configuration. The context in which <code class="docutils literal notranslate"><span class="pre">board_early_initialize()</span></code>
	executes is suitable for early initialization of most, simple
	device drivers and is a logical, board-specific extension of
	up_initialize().</p>
	<p><code class="docutils literal notranslate"><span class="pre">board_early_initialize()</span></code> runs on the startup, initialization
	thread. Some initialization operations cannot be performed on the
	start-up, initialization thread. That is because the
	initialization thread cannot wait for event. Waiting may be
	required, for example, to mount a file system or or initialize a
	device such as an SD card. For this reason, such driver initialize
	must be deferred to <code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code>.</p>
	</dd></dl>

	<dl class="c function">
	<dt class="sig sig-object c" id="c.board_late_initialize">
	<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">board_late_initialize</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.board_late_initialize" title="Permalink to this definition"></a><br /></dt>
	<dd><p>And, finally, just before the user application code starts. If
	<code class="docutils literal notranslate"><span class="pre">CONFIG_BOARD_LATE_INITIALIZE=y</span></code> is selected in the
	configuration, then an final, additional initialization call will
	be performed in the boot-up sequence to a function called
	<code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code>. <code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code> will be
	called well after <code class="docutils literal notranslate"><span class="pre">up_initialize()</span></code> and
	<code class="docutils literal notranslate"><span class="pre">board_early_initialize()</span></code> are called.
	<code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code> will be called just before the main
	application task is started. This additional initialization phase
	may be used, for example, to initialize more complex,
	board-specific device drivers.</p>
	<p>Waiting for events, use of I2C, SPI, etc are permissible in the
	context of board_late_initialize(). That is because
	<code class="docutils literal notranslate"><span class="pre">board_late_initialize()</span></code> will run on a temporary, internal
	kernel thread.</p>
	</dd></dl>

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