Subject: Re: SCSI cd question
To: Jaromir Dolecek <>
From: Zdenek Salvet <>
List: tech-kern
Date: 04/27/2000 19:18:34
> Hi,
> I've bumped into pretty annoying feature of one NEC CD-ROM DRIVE:461, 2.3d.
> It's normally like 6-speed CDROM, but if it encounters error, it slows
> to 1x speed and after a while it changes back to 6x speed. If the
> CD-ROM in drive is not quite as the NEC likes it, this means
> periodic pauses in CD-ROM reading, as the drive tries to adjust speed.
> This is very annoying especially when playing MP3 ;-)

You can add some buffering to your MP3 player :-)

> Is it possible to somehow say the drive that is should stay
> on some speed ?

Yes, SCSI-3 has such command ("read at XX kB/s or slower"),
although it is marked obsolete in current version of the standard.

> e.g. the driver in kernel would keep track of
> how many read errors occured and force the drive to stay
> on low speed if needed.

It's possible, but may be undesirable with better drive reading scratched CD.
I can create manual CD speed control for you if you still want it.
(Adaptive driver would be more work and tuning). 

Zdenek Salvet                                     
Ustav vypocetni techniky Masarykovy univerzity, Brno
tel.: ++420-5-41 512 257                           fax: ++420-5-41 212 747
         God isn't dead, He's just trying to avoid the draft.