From: jim@jagubox.gsfc.nasa.gov (Jim Jagielski)
Subject: Re: Quadra SCSI Problems???
Keywords: Quadra SCSI APS
Lines: 29
Reply-To: jim@jagubox.gsfc.nasa.gov (Jim Jagielski)
Organization: NASA/Goddard Space Flight Center

tzs@stein2.u.washington.edu (Tim Smith) writes:

>> ATTENTION: Mac Quadra owners: Many storage industry experts have
>> concluded that Mac Quadras suffer from timing irregularities deviating
>> from the standard SCSI specification. This results in silent corruption
>> of data when used with some devices, including ultra-modern devices.
>> Although I will not name the devices, since it is not their fault, an
>> example would be a Sony 3.5 inch MO, without the special "Mac-compatible"
>> firmware installed. One solution, sometimes, is to disable "blind writes"

>This doesn't sound right to me.  Don't Quadras use the 53C96?  If so, the
>Mac has nothing to do with the SCSI timing.  That's all handled by the
>chip.  About the only the timing could be wrong is if Apple programs the
>clock registers wrong on the 96.  That, however, should only really hurt
>synchronous transfer, which is not used by the Mac SCSI Manager.

>Furthermore, disabling blind writes should be meaningless on a Quadra.
>On Macs that used the 5380, which is a much lower level SCSI chip, the
>Mac was responsible for the handshake of each byte transferred.  Blind
>mode affected how the Mac handled that handshake.  On the 5396, the
>handshake is entirely handled by the chip.

The docs say that it's a SCSI Manager bug, if this changes things at all...
-- 
    Jim Jagielski               |  "And he's gonna stiff me. So I say,
    jim@jagubox.gsfc.nasa.gov   |   'Hey! Lama! How about something,
    NASA/GSFC, Code 734.4       |   you know, for the effort!'"
    Greenbelt, MD 20771         |

