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<title>Xenomai API: Descriptor Syscall API</title>
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<h1>Descriptor Syscall API<br>
<small>
[<a class="el" href="group__syscall.html">Level 0 API (Syscall API)</a>]</small>
</h1>
<p>
<div class="dynheader">
Collaboration diagram for Descriptor Syscall API:</div>
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<center><table><tr><td><img src="group__descriptor__sys.png" border="0" alt="" usemap="#group____descriptor____sys_map">
<map name="group____descriptor____sys_map">
<area shape="rect" href="group__syscall.html" title="Level 0 API (Syscall API)" alt="" coords="7,5,177,32"></map></td></tr></table></center>
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<p>
<table border="0" cellpadding="0" cellspacing="0">
<tr><td></td></tr>
<tr><td colspan="2"><br><h2>Data Structures</h2></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">struct </td><td class="memItemRight" valign="bottom"><a class="el" href="structa4l__descriptor.html">a4l_descriptor</a></td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Structure containing device-information useful to users. <a href="structa4l__descriptor.html#_details">More...</a><br></td></tr>
<tr><td colspan="2"><br><h2>ANALOGY_xxx_DESC</h2></td></tr>
<tr><td colspan="2">Constants used as argument so as to define the description depth to recover<p>
<a class="anchor" name="ANALOGY_xxx_DESC"></a> <br><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top"><a class="anchor" name="g9bac966c050032d5f29c3205b80ebe74"></a><!-- doxytag: member="descriptor_sys::A4L_BSC_DESC" ref="g9bac966c050032d5f29c3205b80ebe74" args="" -->
#define </td><td class="memItemRight" valign="bottom"><a class="el" href="group__descriptor__sys.html#g9bac966c050032d5f29c3205b80ebe74">A4L_BSC_DESC</a> 0x0</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">BSC stands for basic descriptor (device data). <br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top"><a class="anchor" name="gefe74d60fa5f6c85021c66993d2cf306"></a><!-- doxytag: member="descriptor_sys::A4L_CPLX_DESC" ref="gefe74d60fa5f6c85021c66993d2cf306" args="" -->
#define </td><td class="memItemRight" valign="bottom"><a class="el" href="group__descriptor__sys.html#gefe74d60fa5f6c85021c66993d2cf306">A4L_CPLX_DESC</a> 0x1</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">CPLX stands for complex descriptor (subdevice + channel + range data). <br></td></tr>
<tr><td colspan="2"><br><h2>Functions</h2></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__descriptor__sys.html#g1e2ec4c91556e9bb1d1c54a7fc6e4b28">a4l_sys_desc</a> (int fd, <a class="el" href="structa4l__descriptor.html">a4l_desc_t</a> *dsc, int pass)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Get a descriptor on an attached device. <a href="#g1e2ec4c91556e9bb1d1c54a7fc6e4b28"></a><br></td></tr>
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<hr><h2>Function Documentation</h2>
<a class="anchor" name="g1e2ec4c91556e9bb1d1c54a7fc6e4b28"></a><!-- doxytag: member="descriptor.c::a4l_sys_desc" ref="g1e2ec4c91556e9bb1d1c54a7fc6e4b28" args="(int fd, a4l_desc_t *dsc, int pass)" -->
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<td class="memname">int a4l_sys_desc </td>
<td>(</td>
<td class="paramtype">int </td>
<td class="paramname"> <em>fd</em>, </td>
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<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype"><a class="el" href="structa4l__descriptor.html">a4l_desc_t</a> * </td>
<td class="paramname"> <em>dsc</em>, </td>
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<td class="paramkey"></td>
<td></td>
<td class="paramtype">int </td>
<td class="paramname"> <em>pass</em></td><td> </td>
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<p>
Get a descriptor on an attached device.
<p>
Once the device has been attached, the function a4l_get_desc() retrieves various information on the device (subdevices, channels, ranges, etc.). The function a4l_get_desc() can be called twice:<ul>
<li>The first time, almost all the fields, except sbdata, are set (board_name, nb_subd, idx_read_subd, idx_write_subd, magic, sbsize); the last field , sbdata, is supposed to be a pointer on a buffer, which size is defined by the field sbsize.</li><li>The second time, the buffer pointed by sbdata is filled with data about the subdevices, the channels and the ranges.</li></ul>
<p>
Between the two calls, an allocation must be performed in order to recover a buffer large enough to contain all the data. These data are set up according a root-leaf organization (device -> subdevice -> channel -> range). They cannot be accessed directly; specific functions are available so as to retrieve them:<ul>
<li><a class="el" href="group__descriptor1__lib.html#g4200a3b0f33b20fedeadc0494491cc9c" title="Get an information structure on a specified subdevice.">a4l_get_subdinfo()</a> to get some subdevice's characteristics.</li><li>a4l_get_chaninfo() to get some channel's characteristics.</li><li><a class="el" href="group__descriptor1__lib.html#g1baacb426ed57054a99020c6b2a42baf" title="Get an information structure on a specified range.">a4l_get_rnginfo()</a> to get some range's characteristics.</li></ul>
<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"><tt>[in]</tt> </td><td valign="top"><em>fd</em> </td><td>Driver file descriptor </td></tr>
<tr><td valign="top"><tt>[out]</tt> </td><td valign="top"><em>dsc</em> </td><td>Device descriptor </td></tr>
<tr><td valign="top"><tt>[in]</tt> </td><td valign="top"><em>pass</em> </td><td>Description level to retrieve:<ul>
<li>A4L_BSC_DESC to get the basic descriptor (notably the size of the data buffer to allocate).</li><li>A4L_CPLX_DESC to get the complex descriptor, the data buffer is filled with characteristics about the subdevices, the channels and the ranges.</li></ul>
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<dl class="return" compact><dt><b>Returns:</b></dt><dd>0 on success. Otherwise:</dd></dl>
<ul>
<li>-EINVAL is returned if some argument is missing or wrong; the pass argument should be checked; check also the kernel log ("dmesg")</li><li>-EFAULT is returned if a user <-> kernel transfer went wrong</li><li>-ENODEV is returned if the descriptor is incoherent (the device may be unattached) </li></ul>
<p>References <a class="el" href="descriptor_8h-source.html#l00049">A4L_BSC_DESC</a>, <a class="el" href="descriptor_8h-source.html#l00078">a4l_descriptor::magic</a>, and <a class="el" href="descriptor_8h-source.html#l00080">a4l_descriptor::sbsize</a>.</p>
<p>Referenced by <a class="el" href="descriptor_8c-source.html#l00364">a4l_fill_desc()</a>, and <a class="el" href="descriptor_8c-source.html#l00297">a4l_open()</a>.</p>
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