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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