<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>How commands are processed</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="libATA Developer's Guide" /><link rel="up" href="ch03.html" title="Chapter 3. Error handling" /><link rel="prev" href="ch03s02.html" title="How commands are issued" /><link rel="next" href="ch03s04.html" title="How commands are completed" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">How commands are processed</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch03s02.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Error handling</th><td width="20%" align="right"> <a accesskey="n" href="ch03s04.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="How commands are processed"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2810852"></a>How commands are processed</h2></div></div></div><p> Depending on which protocol and which controller are used, commands are processed differently. For the purpose of discussion, a controller which uses taskfile interface and all standard callbacks is assumed. </p><p> Currently 6 ATA command protocols are used. They can be sorted into the following four categories according to how they are processed. </p><div class="variablelist"><dl><dt><span class="term">ATA NO DATA or DMA</span></dt><dd><p> ATA_PROT_NODATA and ATA_PROT_DMA fall into this category. These types of commands don't require any software intervention once issued. Device will raise interrupt on completion. </p></dd><dt><span class="term">ATA PIO</span></dt><dd><p> ATA_PROT_PIO is in this category. libata currently implements PIO with polling. ATA_NIEN bit is set to turn off interrupt and pio_task on ata_wq performs polling and IO. </p></dd><dt><span class="term">ATAPI NODATA or DMA</span></dt><dd><p> ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this category. packet_task is used to poll BSY bit after issuing PACKET command. Once BSY is turned off by the device, packet_task transfers CDB and hands off processing to interrupt handler. </p></dd><dt><span class="term">ATAPI PIO</span></dt><dd><p> ATA_PROT_ATAPI is in this category. ATA_NIEN bit is set and, as in ATAPI NODATA or DMA, packet_task submits cdb. However, after submitting cdb, further processing (data transfer) is handed off to pio_task. </p></dd></dl></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch03s02.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch03.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch03s04.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">How commands are issued </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> How commands are completed</td></tr></table></div></body></html>
