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You guys just don't get it!
I think I get it, for one?
From what I can see of this conversation, I'm inclined to hope we're actually all in violent agreement already?
I am a BRIDGE and I receive some whacked out command. It may be "standard"
or it may be some vendor specific command. The information about the data
transfer, including byte count and transfer direction, were handled by the host
driver and I am far removed from that So if it's one of your "standard"
commands, I have to look at the command to figure this stuff out. If it's a READ10,
say, I have to go get the damned MODE PAGES from the disk or whatever to
figure out how many BYTES because the CDB has a block count. If it's some
vendor-specific or future command I'm SOL.
Can you hear us now?
I did a bridge in 1998, and I suffered the same pain then. I was doing SCSI over USB to PATAPI, rather than ATA over SCSI to SATA or PATA, but I think that's not a significant difference for this issue.
How to wholly support the vendor-specific and future standard ops is an intriguingly difficult concept to get across in words. I think many people begin by believing the CDB should unequivocally express the expected data copy direction and byte length. They think we should not have to add separate and technically redundant, and therefore potentially contradictory, fields to convey that information.
That perspective is both entirely correct and utterly irrelevant.
The legacy of design for the ATA op and parameters, same as the SCSI op and parameters, has no history of unequivocally expressing the expected direction and length. Only an a priori agreement to convey nothing but old standard ops can escape the need to convey this info redundantly.
Everybody should agree over this. It is a plain truth - a trivially repeatable, empirical, scientific observation - not a matter of debate. It becomes plain - as it did here - so soon as you get to the development stage of writing the code to pass thru an arbitrary command.
Yet still I've never seen this point raised without provoking enough controversy that people give up and drop out of the conversation without having learned to communicate.
I wish I knew why.
Pat LaVarre http://members.aol.com/plscsi/cdbcomplete.html http://ide-byte-counting.blog-city.com
