Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!keith
From: keith@Apple.COM (Keith Rollin)
Newsgroups: comp.sys.mac.programmer
Subject: Re: MemErr and SetGrowZone on IIci
Message-ID: <47484@apple.Apple.COM>
Date: 19 Dec 90 01:31:05 GMT
References: <1CE00001.1p63kl@tbomb.ice.com>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 49

In article <1CE00001.1p63kl@tbomb.ice.com> time@tbomb.ice.com writes:
>
>In article <22228@well.sf.ca.us>, gurgle@well.sf.ca.us (Pete Gontier) writes:
>> In (thinly) related news, we spent hours trying to track down the misbehavior
>> of the low memory global MemErr after a call to SetGrowZone. We had
>> in MacsBug, the instruction 'TST.W MemErr' listed. We'd do a 'dw MemErr' and
>> get an error code we'd never seen before and wasn't listed anywhere. After
>
>This error code was nothing of the sort. It is a pointer to something
>and when looked at as a short appears to be a boagus error code.
>
>> single-stepping the TST, we'd do another 'dw MemErr' and it would turn
>> out to have CHANGED to 0. We finally decided that on the IIci, there
>> was something wrong with the MMU, because this behavior did not appear on
>> other machines. Anybody ever seen or heard of anything like this?
>
>I presume you meant 'dm MemErr' (MacsBug right?). The MemErr global
>is set by the glue code used to implement the SetGrowZone() in your
>high level language (MPW or Think?). Why the TST.W would affect this
>MemErr value I do not know, unless you missed some other code hitting
>it. Sounds like you stepped right through the one instruction properly,
>so it does sound a little wierd. Maybe, because the glue code is supposed
>to treat this as a procedure (no return value) it is setting MemErr
>to noErr to clean up.

Tim,

"dw xxxx" should work fine in Macsbug. "dw" stands for Display Word.

Also, I think that this whole thing with MemErr getting set to zero
was the result of a bug in MacsBug. Macsbug would make a call to the
Graphics Device Manager, which would make a call to the Memory Manager,
which would set MemErr. Therefore, it was Macsbug that was clearing
MemErr.

I'm not sure what versions of Macsbug suffer from the bug.

BTW: I don't know if this is true about SetGrowZone specifically, but
on all ROMs subsequent to the 64K ROMs, the Memory Manager sets MemErr
itself. Previously, this was done by the high-level glue provided by
the development system. In MPW 3.2, this glue has been taken out, along
with support for the 64K ROMs.

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"Argue for your Apple, and sure enough, it's yours" - Keith Rollin, Contusions