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  <TITLE>Specification of IDE DMA YaST2 configuration module</TITLE>
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<!-- $Id: idedma_specification.html 12532 2003-10-30 12:06:48Z lslezak $ -->

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<H2>IDE DMA module specification</H2>

<P>
<I>Author: Ladislav Slezak &lt;<A HREF="mailto:lslezak@suse.cz">
lslezak@suse.cz</A>&gt;</I>
</P>

<P>
Changes:
</P>

<P>
<UL>
  <LI><B>2003-10-29:</B> Added Details section</LI>
  <LI><B>2003-02-14:</B> Update - set transfer DMA mode</LI>
  <LI><B>2002-01-21:</B> Initial version</LI>
</UL>
</P>

<HR>


<H3>Why set IDE DMA mode</H3>

<P>Some IDE devices are broken and they do not work properly if they have DMA
mode enabled (especially CD-ROM drives) or Linux kernel sometimes detect wrong
maximux DMA transfer mode. DMA mode is enabled by kernel after boot for disk
devices and disabled for CD-ROMs. Default DMA mode can be changed by
boot.idedma init script after boot.</P>

<P>This YaST2 module uses boot.idedma initscript which is frontend for hdparm utility.</P>


<H3>Module description</H3>

<P>
In this YaST2 module DMA mode of selected device
can be enabled, disabled or changed (e.g. from UltraDMA/100 to UltraDMA/66).</P>

<P>Features of YaST2 module are available <A HREF="idedma_features.txt">here</A>.</P>

<P>Settings are stored in file /etc/sysconfig/hardware in variable
DEVICES_FORCE_IDE_DMA. This variable contains pairs
&lt;device&gt;:&lt;DMA_mode&gt; separated by space. <EM>Device</EM> is device
file (e.g. /dev/hdc), <EM>DMA_mode</EM> is on (enable default DMA mode), off
(disable DMA mode, use PIO mode instead) or DMA mode specification supported by
hdparm (e.g. mdma2, udma2, udma5,...). </P>

<P>Other devices (not specified in DEVICES_FORCE_IDE_DMA variable) have their
DMA mode unchanged.</P>


<H3>Workflow</H3>

<P>IDE DMA configuration module has only one dialog.</P>

<P>
<IMG SRC="idedma.png">
</P>

<P>There are displayed all attached IDE devices in the table. Column 'Required
DMA mode' contains DMA mode which will be set after 'Finish' button is pressed
and after boot by init script. Other columns contain device information and
current DMA mode.</P>

<P>To change DMA mode select device in the table and select required DMA mode
in combo box below the table. Press Finish to save values to sysconfig/hardware
file and activate changes. </P>

<H3>Details</H3>

<P>Disc cache is flushed (/bin/sync) before DMA is enabled to minimize data loss
if the machine hangs just after enabling DMA.</P>

<P>IDE devices which use ide-scsi emulation (usually CD recorders) can be
also configured by this tool. Their original IDE device name is used to set up
DMA mode.</P>

<P>Although not all DMA modes can be set in the Yast2 module (e.g. UltraDMA/44)
they can be set up manually in the sysconfig file. These modes are read-only
for Yast2 to not confuse users with too many (usually not used) DMA modes.</P>

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