94-176R0 -- Proposed Change for PORT STATUS Command Operation Code

Ralph Weber -- VMS -- ZKO3-4/U14 weber at star.enet.dec.com
Sun Sep 4 14:58:57 PDT 1994


To:       Membership of X3T10

From:     Ralph O. Weber
          Digital Equipment Corporation

Date:     August 25, 1994

Subject:  Proposed Change for PORT STATUS Command Operation Code

Approved document X3T9.2/93-041R2 defines 11h as the operation
code for the PORT STATUS command.  This operation code definition
limits the types of devices that can support the PORT STATUS
command, and thus the types of devices that can offer complete
dual port device support.

Tapes cannot implement the op-code 11h PORT STATUS command
because they are required to support the SPACE command, whose
operation code already is 11h.  Similarly, disks, line printers,
processors, write-once read-many optical devices, and CD-ROM
devices all have operation code 11h marked as vendor-specific
in SCSI-2.

I propose that SCSI-3 assign operation code 1Fh to the PORT
STATUS command.  Operation code 1Fh is currently unassigned (as
far as I know).  Therefore, with the 1Fh op-code, the PORT STATUS
command can be implemented by any SCSI device type.  This allows
full generality in the dual port concepts for SCSI-3.

There is a down-side to this proposal.  Operation code 1Fh is the
last unassigned Group 0 (six-byte CDBs) operation code.  If more
six-byte commands are desired, we would need to either reclaim
some of the currently vendor specific Group 0 operation codes or
define Group 3 to be six-byte commands.

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