Media changers attached to CD-ROM devices currently proh
Falk, Erik
erikf at adicco.wa.com
Wed Nov 23 14:23:54 PST 1994
>FROM: Ralph Weber -- VMS -- ZKO3-4/U14 <weber at star.enet.dec.com>
>
>I have been working through the SPC numeric listing of opcodes.
>During that process, I have discovered that READ ELEMENT STATUS and
>SET CD-ROM SPEED share the B8h opcode. Since READ ELEMENT STATUS is
>a necessary part of an attached medium changer implementation, this
>shared usage of opcodes means that CD-ROM devices cannot have
>attached medium changers.
>
>This seems to prevent a valid use of the attached medium changer
>model. Does anybody care?
>
>Thanks.
>
>Ralph::
Since --any-- removable medium device is a potential candidate for
integration with a medium changer, and also because SPC defines the
"attached medium changer configuration" for a device as responding as
a single logical unit, other potential opcode conflicts exist. All of
these other potential conflicts are carry-overs from SCSI-2, which
excluded the single-logical-unit configuration.
Table B.2 of SPC rev3 shows that these other potential conflicts in
opcode are as follows:
D - DIRECT ACCESS DEVICE Device column key
.T - SEQUENTIAL ACCESS DEVICE M = Mandatory
. L - PRINTER DEVICE O = Optional
. P - PROCESSOR DEVICE V = Vendor-specific
. .W - WRITE ONCE READ MULTIPLE DEVICE R = Reserved
. . R - READ ONLY (CD-ROM) DEVICE
. . S - SCANNER DEVICE
. . .O - OPTICAL MEMORY DEVICE
. . . M - MEDIA CHANGER DEVICE
. . . C - COMMUNICATION DEVICE
. . .
OP DTLPWRSOMC Description
--+----------+--------------------------------------------------------
07 O INITIALIZE ELEMENT STATUS
07 OVV O OV REASSIGN BLOCKS
2B O LOCATE
2B O POSITION TO ELEMENT
2B O OO O SEEK(10)
A5 M MOVE MEDIUM
A5 O PLAY AUDIO(12)
(Please also note that opcode 07h is listed as being both Optional
--and-- Vendor-specific for medium changer devices.)
For these reasons, I propose that the following --optional-- commands
be added to SMC:
INITIALIZE ELEMENT STATUS(10)
+=====================================================================+
| Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|Byte | | | | | | | | |
|=====+===============================================================|
| 0 | Operation code (50h) |
|-----+---------------------------------------------------------------|
| 1 | Reserved |
|-----+---------------------------------------------------------------|
| 2 | Reserved |
|-----+---------------------------------------------------------------|
| 3 | Reserved |
|-----+---------------------------------------------------------------|
| 4 | Reserved |
|-----+---------------------------------------------------------------|
| 5 | Reserved |
|-----+---------------------------------------------------------------|
| 6 | Reserved |
|-----+---------------------------------------------------------------|
| 7 | Reserved |
|-----+---------------------------------------------------------------|
| 8 | Reserved |
|-----+---------------------------------------------------------------|
| 9 | Control |
+=====================================================================+
The INITIALIZE ELEMENT STATUS(10) command would be an optional command
which functions identically to the INITIALIZE ELEMENT STATUS command.
It is intended for use in attached medium changer devices where the
INITIALIZE ELEMENT STATUS command would conflict with the REASSIGN
BLOCKS command.
POSITION MEDIUM TRANSPORT
+=====================================================================+
| Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|Byte | | | | | | | | |
|=====+===============================================================|
| 0 | Operation code (51h) |
|-----+---------------------------------------------------------------|
| 1 | Reserved |
|-----+---------------------------------------------------------------|
| 2 | Reserved |
|-----+---------------------------------------------------------------|
| 3 | Reserved |
|-----+---------------------------------------------------------------|
| 4 | (MSB) |
|-----+--- Destination Element Address ---|
| 5 | (LSB) |
|-----+---------------------------------------------------------------|
| 6 | Reserved |
|-----+---------------------------------------------------------------|
| 7 | Reserved |
|-----+---------------------------------------------------------------|
| 8 | Reserved |
|-----+---------------------------------------------------------------|
| 9 | Control |
+=====================================================================+
The POSITION MEDIUM TRANSPORT command would be an optional command
which functions identically to the POSITION TO ELEMENT command, except
that no transport element address is specified. It is intended for use
in attached medium changer devices where the POSITION TO ELEMENT
command would conflict with the SEEK or LOCATE commands, although it
could also be used by independent medium changer devices which have
only a single medium transport element.
MOVE MEDIUM(10)
+=====================================================================+
| Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|Byte | | | | | | | | |
|=====+===============================================================|
| 0 | Operation code (52h) |
|-----+---------------------------------------------------------------|
| 1 | Reserved |
|-----+---------------------------------------------------------------|
| 2 | (MSB) |
|-----+--- Source Element Address ---|
| 3 | (LSB) |
|-----+---------------------------------------------------------------|
| 4 | (MSB) |
|-----+--- Destination Element Address ---|
| 5 | (LSB) |
|-----+---------------------------------------------------------------|
| 6 | Reserved |
|-----+---------------------------------------------------------------|
| 7 | Reserved |
|-----+---------------------------------------------------------------|
| 8 | Reserved | Inv |
|-----+---------------------------------------------------------------|
| 9 | Control |
+=====================================================================+
The MOVE MEDIUM(10) command would be an optional command which
functions identically to the MOVE MEDIUM command, except that no
transport element address is specified. It is intended for use in
attached medium changer devices where the MOVE MEDIUM command would
conflict with the PLAY AUDIO(12) command, although it could also be
used by independent changer devices which have only a single medium
transport element.
In addition to adding the above commands to SMC, those opcodes
specific to medium changer devices, and which do not conflict with
existing SCSI-2 opcodes, should be excluded from assignment to SCSI-3
removable medium device command sets (SBC, SSC, MMC, etc). This means
that the SET
CD-ROM SPEED command would need to be assigned to a different opcode.
The restricted opcodes would be as follows, subject to revision of SMC
as proposed:
COMMAND OPERATION CODE
------------------------------ --------------
INITIALIZE ELEMENT STATUS(10) 50h
POSITION MEDIUM TRANSPORT 51h
MOVE MEDIUM(10) 52h
EXCHANGE MEDIUM A6h
REQUEST VOLUME ELEMENT ADDRESS B5h
SEND VOLUME TAG B6h
READ ELEMENT STATUS B8h
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