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