ANOTHER BIT IN INQUIRY DATA

Tom Wicklund wicklund at intellistor.com
Thu Aug 25 14:13:02 PDT 1994


John Lohmeyer asked:

   Should we add a bit to the INQUIRY Data to say
   the target supports Fast-20 to avoid any nasty surprises?

How do current initiators handle fast SCSI?  There is no INQUIRY bit
yet devices appear to be able to differentiate between the SCSI-1
200ns transfer period and SCSI-2's 100ns period.

It seems reasonable to assume that the same logic which prevents fast
SCSI problems will prevent FAST-20 SCSI problems.

If there are currently problems with the current fast SCSI and earlier
devices then perhaps a better solution is a byte someplace which
specifies the minimum transfer period the device can handle.

A further problem with the INQUIRY bit is that many initiators and
targets negotiate synchronous as their first action.  It's hard to get
INQUIRY data to decide on a data rate before the first data phase.  Of
course, one could negotiate a slower speed, get the INQUIRY data, then
negotiate the real speed, but this is getting awfully complicated in
order to work around what is probably a bug in device microcode.




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