REQUIRE AN IDENTIFY MESSAGE IN SIP
wicklund at intellistor.com
Tue Aug 16 09:36:57 PDT 1994
Gerry Houlder writes:
> This is the change proposed by Giles:
> >"The first message sent by the initiator after the SELECTION phase
> >shall be an IDENTIFY, ABORT, or BUS DEVICE RESET message. If a target
> >receives any other message it shall issue a BUS FREE request."
> >All that is needed is to reword the last sentence as follows:
> > "If -ATN IS NOT ACTIVATED OR IF the target receives any other
> > message..." (CAPS indicate the change.)
> This change means that SCSI-3 targets cannot function in SCSI-1 or SCSI-2
> systems that use selection without ATN. This will absolutely require initiators
> to put the drive in "SCSI-2 mode" or "SCSI-3 mode" before installing it in the
> system. Or it could require target manufacturers to support even more different
> and unique code versions than we have to now. I don't think this is a good
> idea. The target manufacturer's problem of selling a SCSI drive to a
> distributor and having that drive work in a wide variety of SCSI-1, SCSI-2, or
> SCSI-3 systems and have it be able to plug and play (not necessarily a
> reference to the Plug and Play SCSI proposal) will become impossible.
I don't see how this will be true.
SCSI-2 already requires that the IDENTIFY message be used to identify
the logical unit -- (see section 7.2.2), yet I'm sure most SCSI-2
devices will also accept SCSI-1 selection without the IDENTIFY message
and use the LUN field in the CDB (especially when popular systems like
Sun issue selection without IDENTIFY during system boot).
In the same way, I don't see why a SCSI-3 device might not accept
selection without ATN as a signal to revert to SCSI-1 operation. It
might fail a strict SCSI-3 compliance tester, but won't affect normal
operation on a "real" system.
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