This message is from the T13 list server.
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.
Quoting...
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.
Jeff
