Re: CD changers

Gadi Oxman (
Sat, 7 Mar 1998 08:11:12 +0300 (IST)

On Fri, 6 Mar 1998, Wakko Warner wrote:

> Isn't there some way of having the kernel detect how many units there are on
> a cdrom drive and assign like (assuming the drive is hdd) the current slot
> to hdd (like it is now, or maybe it be the first slot), then hdd1 is slot1?
> Or isn't there a way to have the ide-scsi detect more than 1 lun on the
> device?

CD changers is one area in which the ATAPI model is different than the
SCSI model.

The firmware in a SCSI CD changer handles each slot as a different logical
unit, but the ATAPI CDROM specification supports one "active" slot in
combination with a "change active slot" command.

I had assumed that perhaps, if the ATAPI model of various vendors was
internally based on the SCSI model, perhaps the functionality will still
be available in the firmware, and the ide-scsi driver would be able to
"restore" the hidden firmware functionality. Apparently this is not the
case, and current ATAPI changers do not support multiple logical units in
the firmware.

We can try to emulate this SCSI firmware functionality in software, using
multiple queues in the IDE driver, one for each slot, and issuing the "change
slot" command whenever we switch queue. This is not a trivial change, however.


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