About CD-ROM READ(10) Command

Gerry_Houlder at notes.seagate.com Gerry_Houlder at notes.seagate.com
Tue Apr 21 14:24:27 PDT 1998

* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Gerry_Houlder at notes.seagate.com
This brings up a question of what should be specified in the standard.
Clearly the T10 standard permits either action by the target. However, this
means that even a careful target designer could end up with a product that
doesn't conform to the expectations of the initiator. It also means that
targets are implemented with different firmware for different customers to
conform to their different expectations. Also note that option (a) is
defined as the PREFETCH command in the SCSI standard. If PREFETCH is
implemented, is it also proper to do the same thing for READ with zero
transfer length? Should PREFETCH be obsoleted if option (a) is the defined
resopnse for READ with zero transfer length?

The READ commands are defined separately in each command set document. Many
cases just refer to the SBC document for the command description. Perhaps
it is time to define a READ for CD ROM that defines the action in this
situation if it is not possible to get enough support to change the SBC

If no further guidance is possible from the standard, It is probably safer
for a target to implement option (a). This will satisfy initiators that
expect this operation. It probably will not cause a problem for initiators
that expect option (b), because that option doesn't promise any particular
operation. What do the host vendors think of this?

>   Could you advice us that which interpretation is right about
> this command, (a) or (b) ?
>       (a) Even if transfer length=0, seek to Logical Block Address
>            and buffering to drive RAM from medium, then finish.
>       (b) Because of transfer length=0, NO seek operation, and
>            NO buffering from medium, then finish.

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