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  31 <h1>Descriptor Syscall API<br>
  32 <small>
  33 [<a class="el" href="group__syscall.html">Level 0 API (Syscall API)</a>]</small>
  34 </h1>
  35 <p>
  36 <div class="dynheader">
  37 Collaboration diagram for Descriptor Syscall API:</div>
  38 <div class="dynsection">
  39 <center><table><tr><td><img src="group__descriptor__sys.png" border="0" alt="" usemap="#group____descriptor____sys_map">
  40 <map name="group____descriptor____sys_map">
  41 <area shape="rect" href="group__syscall.html" title="Level 0 API (Syscall API)" alt="" coords="7,5,177,32"></map></td></tr></table></center>
  42 </div>
  43
  44 <p>
  45 <table border="0" cellpadding="0" cellspacing="0">
  46 <tr><td></td></tr>
  47 <tr><td colspan="2"><br><h2>Data Structures</h2></td></tr>
  48 <tr><td class="memItemLeft" nowrap align="right" valign="top">struct &nbsp;</td><td class="memItemRight" valign="bottom"><a class="el" href="structa4l__descriptor.html">a4l_descriptor</a></td></tr>
  49
  50 <tr><td class="mdescLeft">&nbsp;</td><td class="mdescRight">Structure containing device-information useful to users.  <a href="structa4l__descriptor.html#_details">More...</a><br></td></tr>
  51 <tr><td colspan="2"><br><h2>ANALOGY_xxx_DESC</h2></td></tr>
  52 <tr><td colspan="2">Constants used as argument so as to define the description depth to recover<p>
  53 <a class="anchor" name="ANALOGY_xxx_DESC"></a> <br><br></td></tr>
  54 <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="" -->
  55 #define&nbsp;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__descriptor__sys.html#g9bac966c050032d5f29c3205b80ebe74">A4L_BSC_DESC</a>&nbsp;&nbsp;&nbsp;0x0</td></tr>
  56
  57 <tr><td class="mdescLeft">&nbsp;</td><td class="mdescRight">BSC stands for basic descriptor (device data). <br></td></tr>
  58 <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="" -->
  59 #define&nbsp;</td><td class="memItemRight" valign="bottom"><a class="el" href="group__descriptor__sys.html#gefe74d60fa5f6c85021c66993d2cf306">A4L_CPLX_DESC</a>&nbsp;&nbsp;&nbsp;0x1</td></tr>
  60
  61 <tr><td class="mdescLeft">&nbsp;</td><td class="mdescRight">CPLX stands for complex descriptor (subdevice + channel + range data). <br></td></tr>
  62 <tr><td colspan="2"><br><h2>Functions</h2></td></tr>
  63 <tr><td class="memItemLeft" nowrap align="right" valign="top">int&nbsp;</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>
  64
  65 <tr><td class="mdescLeft">&nbsp;</td><td class="mdescRight">Get a descriptor on an attached device.  <a href="#g1e2ec4c91556e9bb1d1c54a7fc6e4b28"></a><br></td></tr>
  66 </table>
  67 <hr><h2>Function Documentation</h2>
  68 <a class="anchor" name="g1e2ec4c91556e9bb1d1c54a7fc6e4b28"></a><!-- doxytag: member="descriptor.c::a4l_sys_desc" ref="g1e2ec4c91556e9bb1d1c54a7fc6e4b28" args="(int fd, a4l_desc_t *dsc, int pass)" -->
  69 <div class="memitem">
  70 <div class="memproto">
  71       <table class="memname">
  72         <tr>
  73           <td class="memname">int a4l_sys_desc           </td>
  74           <td>(</td>
  75           <td class="paramtype">int&nbsp;</td>
  76           <td class="paramname"> <em>fd</em>, </td>
  77         </tr>
  78         <tr>
  79           <td class="paramkey"></td>
  80           <td></td>
  81           <td class="paramtype"><a class="el" href="structa4l__descriptor.html">a4l_desc_t</a> *&nbsp;</td>
  82           <td class="paramname"> <em>dsc</em>, </td>
  83         </tr>
  84         <tr>
  85           <td class="paramkey"></td>
  86           <td></td>
  87           <td class="paramtype">int&nbsp;</td>
  88           <td class="paramname"> <em>pass</em></td><td>&nbsp;</td>
  89         </tr>
  90         <tr>
  91           <td></td>
  92           <td>)</td>
  93           <td></td><td></td><td></td>
  94         </tr>
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  96 </div>
  97 <div class="memdoc">
  98
  99 <p>
 100 Get a descriptor on an attached device.
 101 <p>
 102 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>
 103 <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>
 104 <p>
 105 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 -&gt; subdevice -&gt; channel -&gt; range). They cannot be accessed directly; specific functions are available so as to retrieve them:<ul>
 106 <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>
 107 <p>
 108 <dl compact><dt><b>Parameters:</b></dt><dd>
 109   <table border="0" cellspacing="2" cellpadding="0">
 110     <tr><td valign="top"><tt>[in]</tt>&nbsp;</td><td valign="top"><em>fd</em>&nbsp;</td><td>Driver file descriptor </td></tr>
 111     <tr><td valign="top"><tt>[out]</tt>&nbsp;</td><td valign="top"><em>dsc</em>&nbsp;</td><td>Device descriptor </td></tr>
 112     <tr><td valign="top"><tt>[in]</tt>&nbsp;</td><td valign="top"><em>pass</em>&nbsp;</td><td>Description level to retrieve:<ul>
 113 <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>
 114 </td></tr>
 115   </table>
 116 </dl>
 117 <dl class="return" compact><dt><b>Returns:</b></dt><dd>0 on success. Otherwise:</dd></dl>
 118 <ul>
 119 <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 &lt;-&gt; kernel transfer went wrong</li><li>-ENODEV is returned if the descriptor is incoherent (the device may be unattached) </li></ul>
 120
 121 <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>
 122
 123 <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>
 124
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