Subject: Re: SCSI CD changers supported?
To: None <current-users@NetBSD.ORG>
From: Tom I Helbekkmo <tih@Hamartun.Priv.NO>
List: current-users
Date: 09/10/1996 13:56:59
My thanks again to those who helped me get my Pioneer DRM-610 CD
changer online, and particularly to Michael L. Hitch, whose advice
also enabled me to get an old tape station operative.

There are still a couple of problems with the DRM-610, though.  The
first is that it takes 5-6 seconds for it to change CDs, which
wouldn't be too bad except that the whole SCSI bus is locked during
this time, which is sort of silly.  It gets especially bad when I
exercise it a bit harder, by working actively on two CDs at the same
time: after a couple of changes, the system will panic with a timeout
on one of my magnetic disk drives.  I'm guessing that a command to the
disk drive happens to be sent to the controller after commands have
been queued that will demand two CD changes before the command for the
disk will be processed, and the jump from 5-6 seconds to 10-12 causes
some timeout limit in the SCSI driver to be reached.  Is there no way
around this sort of thing?  Couldn't the driver ask the controller how
the command is faring, and be told "hold your horses; we're getting
around to it"?

The other problem is one of throughput, quite simply.  Using dd(1) to
sequentially read a large file from a CD, and dumping it to /dev/null,
I get about 6 kilobytes per second.  There are no error messages, but
I suspect a hardware problem with the Pioneer unit, as my magnetic
disks all show periodic brief spurts of activity while the CD is being
read, as if they only get access to the SCSI bus once in a while, for
a split second, and then have to wait for the CD again.  This looks to
me like the CD player may be having trouble reading its disk, and then
having to retry lots and lots of times for every read operation.

Any hints regarding how to research this problem would be appreciated!

nothing really rocks and nothing really rolls and nothing's ever worth the cost