Subject: SCSI chips
To: None <>
From: David Jones <>
List: amiga
Date: 10/07/1994 13:28:09
> >I've been getting this error (with subsequent disk lockup) intermittently
> >(once 4 times in an hour) under heavy scsi disk load.  Any hints?
> I believe a BETA a3000 SCSI controller may cause SCSI lockups.
> May this be the case?


There are two versions of the WD3393 SBIC used in the A3000.  The older version
has a microcode bug that can cause the bus to lock when driven by naive
SCSI drivers.

The bad version of the chip is one of the following:
WD33c93-00-04 or Am33c93A

(The presence or absence of the word "PROTO" is not indicative)

The good version of the chip is one of the following:

WD33c93-00-08, WD33c93B, WD33c93C, Am33c93B, Am33c93C

The WD parts are available from Western Digital, and the Am parts are available
from Advanced Micro Devices, who are second-sourcing the WD design.

You can easily open up your Amiga and take a look.

HOWEVER... starting with vmunix.644 (about a year ago today!) or so, the sbic
driver has had hacks that work around all known microcode bugs.  I am running
a WD33c93-00-04 (bad), with a Maxtor LXT7345S and Quantum Q105S and Insite
Floptical, with NO lockups EVER from vmunix.644 onward.  That doesn't mean that
the bugs are completely fixed, but it gives me a lot of confidence.

If you think the "beta" SCSI chip is causing your problem, then feel free to
find a "good" chip from one of the parts listed above, and try it.

David Jones, M.A.Sc student, Electronics Group (VLSI), University of Toronto
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