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Path: utzoo!linus!decvax!duke!mcnc!ncsu!ncrcae!wescott
From: wescott@ncrcae.UUCP
Newsgroups: net.micro.68k
Subject: yet another 68k complaint
Message-ID: <1033@ncrcae.UUCP>
Date: Sat, 24-Dec-83 01:08:25 EST
Article-I.D.: ncrcae.1033
Posted: Sat Dec 24 01:08:25 1983
Date-Received: Tue, 27-Dec-83 03:18:22 EST
Lines: 19



Yet another 68k problem.  We have found the following
bug/feature (it was quite an annoyance finding it too!).
The movem instruction in the 68k, when reading from memory
into registers does an additional read cycle at the end
of the transfer addressing one word beyond that required.

No harm done, in most cases when the use is to save/restore
registers on the stack. But the movem op has also been used
to implement some fast bulk move routines (like blt, which
came with the MIT compiler, I believe.) If the routine
happens to use its movem op right up to the edge of a
segment the extra read can cause a bus error where
one is not expecting it.


Michael Wescott, NCR Corp., Columbia SC
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