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  <section id="auto-mounter">
<h1>Auto-Mounter<a class="headerlink" href="#auto-mounter" title="Permalink to this heading"></a></h1>
<section id="general-description">
<h2>General Description<a class="headerlink" href="#general-description" title="Permalink to this heading"></a></h2>
<p>NuttX implements an auto-mounter than can make working with SD cards or other
removable media easier. With the auto-mounter, the file system will be
automatically mounted when media is inserted and automatically unmounted when
the media is removed.</p>
<p>The auto is enable by selecting in the NuttX configuration:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>CONFIG_FS_AUTOMOUNTER=y
</pre></div>
</div>
<p>WARNING: SD cards should never be removed without first unmounting them. This
is to avoid data and possible corruption of the file system. Certainly this is
the case if you are writing to the SD card at the time of the removal. If you
use the SD card for read-only access, however, then I cannot think of any
reason why removing the card without mounting would be harmful.</p>
<p>For applications that write to the removable media, the automatic unmount is
still beneficial (as opposed to leaving a broken mount in place) although
should not be relied upon for a proper solution.</p>
</section>
<section id="board-specific-support">
<h2>Board-Specific Support<a class="headerlink" href="#board-specific-support" title="Permalink to this heading"></a></h2>
<p>Like many components of NuttX, the auto-mounter has a upper-half/lower-half
architecture:</p>
<ul class="simple">
<li><p><strong>Upper half</strong> The upper half is the file <code class="docutils literal notranslate"><span class="pre">fs/fs_automount.c</span></code>. This upper
half performs the basic automount activities. It responds to media
insertion and removal events by mounting and unmounting the file system on
the media. This includes logic to handle unmount retries: The unmount cannot
be performed while applications have open files on the media. In this case,
the auto-mounter will periodically retry the unmount until all of the
applications close there references to files on the non-existent media.</p></li>
<li><p><strong>Lower Half</strong> The lower half is defined by a standard interface. That
interface definition is in the header file <code class="docutils literal notranslate"><span class="pre">include/nuttx/fs/automount.h</span></code>.
The lower half interface provides: (1) mount information including file
system type, block driver path, and mount point path, (2) mount and unmount
retry delays, and (3) and callbacks to attach to and management the media
insertion / removal interrupts.</p></li>
</ul>
</section>
<section id="example-implementation">
<h2>Example Implementation<a class="headerlink" href="#example-implementation" title="Permalink to this heading"></a></h2>
<p>There is an example implementation of this lower half interface at
<code class="docutils literal notranslate"><span class="pre">boards/arm/sama5/sama5d4-ek/src/sam_automount.c</span></code>. The <code class="docutils literal notranslate"><span class="pre">boards/arm/sama5/sama5d4-ek/Kconfig</span></code>
as the board-specific configuration for the auto-mounter. You can see
the configuration settings in the <code class="docutils literal notranslate"><span class="pre">boards/arm/sama5/sama5d4-ek/configs/nsh/defconfig</span></code>
and <code class="docutils literal notranslate"><span class="pre">boards/arm/sama5/sama5d4-ek/configs/nxwm/defconfig</span></code> configuration files:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT=y
CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_FSTYPE=&quot;vfat&quot;
CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_BLKDEV=&quot;/dev/mmcsd0&quot;
CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_MOUNTPOINT=&quot;/mnt/sdcard&quot;
CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_DDELAY=1000
CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_UDELAY=2000
</pre></div>
</div>
<p>These setting determine the values in the lower half interface. The interrupt is
provided by a PIO pin defined in <code class="docutils literal notranslate"><span class="pre">boards/arm/sama5/sama5d4-ek/src/sama5e4-ek.h</span></code> and
the implementation of the interface and callbacks is in
<code class="docutils literal notranslate"><span class="pre">boards/arm/sama5/sama5d4-ek/src/sam_automount.c</span></code>.</p>
</section>
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