Newsgroups: comp.sys.atari.st
Path: utzoo!lsuc!jimomura
From: jimomura@lsuc.on.ca (Jim Omura)
Subject: Re: Bug in TT hardware?
Organization: Consultant, Toronto
Date: Tue, 28 May 1991 13:02:52 GMT
Message-ID: <1991May28.130252.3634@lsuc.on.ca>
References: <1991May27.101719.2923@rhrk.uni-kl.de>

In article <1991May27.101719.2923@rhrk.uni-kl.de> seimet@rhrk.uni-kl.de (Uwe Seimet [Chemie]) writes:
>
>Did anyone ever try to save the last four bytes of TT-RAM on the TT's
>internal hard disk? This operation always fails because the scsi
>controller reports a bus error. (You don't get any bombs, because it's
>not a processor-related error. The hard disk driver simply aborts with
>the usual alert.)
>This problem doesn't seem to be driver dependant. It looks as if the
>controller tries to access not only the last bytes of TT-RAM but some
>bytes on higher adresses, too. Of course, at these adresses there is
>no RAM, so this explains the bus error. If the last byte to transfer
>lies at least four bytes below the end of the physical RAM everything
>is fine.
>Is there any reasonable explanation or is this some kind of hardware
>bug?
>


     It sounds like the 68030 has "pre-fetch" active.  You can
shut this off "manually".  Check a 68030 instruction list.  The
only problem might be that the "pre-fetch" might be built into
the driver and not over-rideable without writing your own driver.
That's probably not going to be a problem, but I've never seen
the code so I can't say.
-- 
Jim Omura, 2A King George's Drive, Toronto, (416) 652-3880
lsuc!jimomura
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