[SeaBIOS] IDE DMA initialization

Magnus Christensson mch at virtutech.com
Tue Jan 19 15:58:24 CET 2010

On 01/14/2010 02:48 PM, Kevin O'Connor wrote:
> On Thu, Jan 14, 2010 at 10:48:33AM +0100, Magnus Christensson wrote:
>> Hi,
>> The recently introduced DMA support in Seabios fails to work on
>> Virtutech Simics. The reason is that DMA has not enabled in the
>> disk. I'm trying to figure out if this is a bug in my setup of
>> Simics, or a bug in Seabios. Shouldn't Seabios enable DMA in the
>> disk through the SET FEATURES command?
> My read of the spec was that the set_features command was only needed
> to specify which dma mode was desired, and that the drive would
> default into mwdma mode by default.  I'll take a closer look through
> the spec this weekend.  The current code does seem to work with the
> real drives I have.
The spec does suggest that mwdma mode is default after power-up. I'll 
change Simics' device model.
> In either case though, we probably should have a CONFIG_ATA_DMA
> define to manually disable that support.
Good. CONFIG_ATA_DMA does work now with Simics, and we'll keep it on 
since it provides a significant performance improvement (rep 
i/o-operations are not handled very efficiently in Simics).


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