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From: peterk@cbmger.UUCP (Peter Kittel GERMANY)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Assembly question from turnip
Keywords: can allocmem crash?
Message-ID: <543@cbmger.UUCP>
Date: 30 Oct 90 13:31:59 GMT
References: <2169@lpami.wimsey.bc.ca> <1990Oct29.205140.28826@zorch.SF-Bay.ORG>
Reply-To: peterk@cbmger.UUCP (Peter Kittel GERMANY)
Organization: Commodore Bueromaschinen GmbH, West Germany
Lines: 23

In article <1990Oct29.205140.28826@zorch.SF-Bay.ORG> xanthian@zorch.SF-Bay.ORG (Kent Paul Dolan) writes:
>lphillips@lpami.wimsey.bc.ca (Larry Phillips) writes:
>
>>There is no guarantee that the last operation to affect the condition codes is
>>the one you are interested in (the move of the result to D0). In other words,
>>the result might be moved to D0, then something else moved to or from another
>>data reg, before control is returned to your program.
>
>WHAT? How can you do multitasking at  all,  if  whatever's  the  68000's
>version of the program status register's set of condition  flags,  isn't
>restored after a context switch?
                  ^^^^^^^
He didn't talk about a context switch but about returning from a
system function called by your program, and this hasn't anything
to do with multitasking and task switching. He explained what can
happen near the very end of such a library routine, shortly before
the finishing RTS. The simple summary is: Do a TSTB or other check
for the flags by your own, but don't rely on the flags being set
just after RTSing.

-- 
Best regards, Dr. Peter Kittel  // E-Mail to  \\  Only my personal opinions... 
Commodore Frankfurt, Germany  \X/ {uunet|pyramid|rutgers}!cbmvax!cbmger!peterk