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I think if you are going to talk about queuing and ATAPI on SATA, you
should just say no and go for a SAS solution. Because that's what SAS
is for.
At 11:08 AM -0500 11/15/05, Jeff Garzik wrote:
This message is from the T13 list server.
Hale Landis wrote:
Jeff Garzik wrote:
It's more than just that. Given that there is no READ FPDMA nor
WRITE FPDMA commands that are applicable to ATAPI, one would have
to contemplate use of a tagging system buried inside the command
set [SCSI].
Hmmm... I don't understand your comment... The tag number is in the
Sector Count register bits 7-3 for R/W DMA QUEUED, PACKET and R/W
FPDMA. Why would the tag need to be inside the PACKET SCSI CDB?
More generally, there is an inherent conflict between ATA queueing
and queueing that's already defined by the command set.
If we are to support ATAPI NCQ, I would think that would involve
some amount of coupling inside the device firmware between the ATA
and SCSI command responses, and behaviors.
If you think about it the FPDMA command codes were never needed. The
True.
But there is a strong ATA tradition to create new command codes for
minor variations of the same basic command
True. And its a silly tradition.
The PACKET command has never needed all this confusion of multiple
command codes for PIO or DMA or overlap/queuing because the PACKET
command uses the Features register as a way to select protocol and
execution options. So the OVL bit (in the PACKET command Features
register) could be used to select 'ncq' on a SATAPI device. But
again,
True.
What do I mean?
The SATA documents, pick one, ATA/ATAPI-7 or the secret society
specification, do not contain the equivalent to the PATA command
protocol state diagrams. The best you can find is ATA/ATAPI-7's
Annex J that is informative. I know a lot of people think the PATA
command protocol state diagrams are used to describe the SATA
command protocol but this is wrong and misleading. SATA is not
PATA. SATA is very
[...]
Ultimately, SATA is just a protocol for transporting anonymous data
packets. There, no state diagrams needed...
Jeff
--
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I make stuff go.
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Larry Barras
ATA CPU Software
Apple Computer Inc.
