SCSI Tagged Queueing And Autosense
Alan Spalding (714) 932-5916
SPALDING_AL at a1.WDC.com
Fri Dec 22 18:49:00 PST 1995
* From the SCSI Reflector, posted by:
* <"Alan Spalding (714) 932-5916" <SPALDING_AL at A1.WDC.COM>>
Date: Fri, 22 Dec 1995 01:38 PST
Subject: SCSI Tagged Queueing Vs Autosense Question
Sender: "wdcscsi-owner at dt.wdc.com" <WDCSCSI-OWNER at DT.WDC.COM>
To: "WDCSCSI at dt.wdc.com" <WDCSCSI at DT.WDC.COM>
Posting-date: Fri, 22 Dec 1995 07:00 PST
Date: Fri, 22 Dec 1995 00:43 PST
Subject: Tagged Queueing Vs AutoSense question
Sender: "Alan Spalding (714) 932-5916" <SPALDING_AL at A1.WDC.COM>
To: Alan Spalding <SPALDING_AL at A1.WDC.COM>
Posting-date: Fri, 22 Dec 1995 01:36 PST
I'm not particularily familiar with Tagged queueing and would like make sure I
have understood the SCSI-2 spec correctly.
A specific question that I have is how a SCSI HBA should implement autosense. My
first thought was that when a check condition is reported an untagged request
sense should be issued. But my understanding of the spec is that when this R.S.
has completed any queued commands will be restarted (unless QErr bit is set to
0). This would seem to be incorrect for certain error conditions such as
replaced media - maybe the device aborts I/Os when the media is replaced). Is
the only safe algorithm to use:
on receipt of the check condition - issue either an abort tag msg for each I/O
in the queue or a clear queue message prior to issuing the untagged R.S.?
Am I correct in my assumption that the first untagged command restarts the
suspended queue and that any tagged commands issued prior to the first untagged
command will simply be queued in the device queue?
alan spalding (internet spalding_al at a1.wdc.com)
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