[t13] SAT: Reminder - Teleconference Thur 8/12 9:00 AM PDT

Jeff Garzik jgarzik at pobox.com
Wed Aug 11 19:28:28 PDT 2004

* From the T10 Reflector (t10 at t10.org), posted by:
* Jeff Garzik <jgarzik at pobox.com>
Curtis Stevens wrote:
>             Just a heads up, I posted a proposal (04-260.PDF) for 
> documenting how a SCSI command maps to an ATA command.

Another quick comment.  Sorry I didn't include this in the first email.

> The host shall set the DEV bit to 0 and the device shall ignore the DEV 
> bit. This is required because the presence of multiple devices cannot be 
> detected. If multiple devices are present on a single cable, the host 
> may indicate this to the host software by reporting multiple LUNs. If 
> there are multiple LUNs, the bridge shall set the DEV bit to the 
> appropriate value before setting the ATA command register.

I agree with this, but for a reason not stated:

If the SAT translator software exports ATA devices as individual SCSI 
targets (rather than LUNs), then the DEV bit is irrelevant at the ATA 
passthru level.  The low-level ATA driver _must_ set or clear the DEV 
bit as appropriate, and the SCSI I/T nexus provides all the information 
necessary to do so.

And a parting shot:  existing SATA controllers _do_ occasionally present 
SATA devices as master/slave.  Several (Intel, SiS, VIA, others?) have a 
compatibility mode that in current hardware is often enabled by default, 
presenting two SATA devices as a master/slave pair.


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