1<html><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 V1.78.1"><link rel="home" href="index.html" title="libATA Developer's Guide"><link rel="up" href="libataEH.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 bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><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"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1120618924"></a>How commands are processed</h2></div></div></div><p> 2 Depending on which protocol and which controller are used, 3 commands are processed differently. For the purpose of 4 discussion, a controller which uses taskfile interface and all 5 standard callbacks is assumed. 6 </p><p> 7 Currently 6 ATA command protocols are used. They can be 8 sorted into the following four categories according to how 9 they are processed. 10 </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">ATA NO DATA or DMA</span></dt><dd><p> 11 ATA_PROT_NODATA and ATA_PROT_DMA fall into this category. 12 These types of commands don't require any software 13 intervention once issued. Device will raise interrupt on 14 completion. 15 </p></dd><dt><span class="term">ATA PIO</span></dt><dd><p> 16 ATA_PROT_PIO is in this category. libata currently 17 implements PIO with polling. ATA_NIEN bit is set to turn 18 off interrupt and pio_task on ata_wq performs polling and 19 IO. 20 </p></dd><dt><span class="term">ATAPI NODATA or DMA</span></dt><dd><p> 21 ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this 22 category. packet_task is used to poll BSY bit after 23 issuing PACKET command. Once BSY is turned off by the 24 device, packet_task transfers CDB and hands off processing 25 to interrupt handler. 26 </p></dd><dt><span class="term">ATAPI PIO</span></dt><dd><p> 27 ATA_PROT_ATAPI is in this category. ATA_NIEN bit is set 28 and, as in ATAPI NODATA or DMA, packet_task submits cdb. 29 However, after submitting cdb, further processing (data 30 transfer) is handed off to pio_task. 31 </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="libataEH.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> 32