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Date:      Thu, 18 Jul 1996 21:03:45 +0200 (MET DST)
From:      J Wunsch <j@uriah.heep.sax.de>
To:        freebsd-scsi@freebsd.org
Subject:   CD driver
Message-ID:  <199607181903.VAA06840@uriah.heep.sax.de>

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Hi all,

i'm currently playing with some improvements to the (SCSI) CD driver.
I've got the first prototype of multi-track support already running,
and have been playing a little with CD-DA.  (Sheesh, i should really
get a soundcard, i guess. :)

Alas, it seems that each vendor picked a different method to allow
digital reading of CD-DA tracks.  The SCSI-2 specs made the IMHO big
mistake to forbid reading these data with a regular READ command.
(The drive _must_ return BLANK CHECK / Illegal mode for this track
when attempting to read CD-DA data.)  So now, some of the vendors
apparently enable it by using a vendor-specific `density code' in the
MODE SELECT block descriptor (0x82, applicable to at least the Toshiba
3401 and higher), followed by a regular read.  Other drives seem to
use a specific command (0xd8) that is similar to READ(12) but reads
audio data (reported for Plextor, my Toshiba 3401 can also do this,
but, the Toshiba 3501 rejects it).  I didn't find anything specific in
the CD-R writer specs for my Plasmon, so i assume it can read them
regularly (perhaps requires a MODE SELECT with a block size of 2352
before, i have to test this).

The big question now is how to place the hooks in the CD driver that
allow for the various methods, and how to assign/enable the hooks.
They must be applicable to each device separately, since it's
certainly possible that someone has two or more different drives.  I
thought of using LKM's for it, but think this will be difficult for
multiple different drives.


While we are at it, does anybody know of other methods to enable
CD-DA?

-- 
cheers, J"org

joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)



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