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From: dave@tygra.ddmi.com (David Conrad)
Newsgroups: comp.lang.pascal
Subject: Re: Problems with interrupt handler for interrupt 08 or 1C in TP 6.0
Message-ID: <1991Jan7.112746.8829@tygra.ddmi.com>
Date: 7 Jan 91 11:27:46 GMT
References: <11648@j.cc.purdue.edu> <139.2787282f@vax1.cc.lehigh.edu>
Organization: Moore Software, Detroit, MI
Lines: 31

In article <139.2787282f@vax1.cc.lehigh.edu> lukrw@vax1.cc.lehigh.edu writes:
>                                                The other thing to
>be very careful of is the stack size at the time of the interrupt.  
>It is very unpredictable, and you may be running out and not know it.
>Be sure to turn off all runtime check to help keep your interrupt
>from overflowing the stack, and keep the processing to an absolute
>minimum (try not to use any procedures or local variables as well).
>It is possible to switch to an alternate stack using an assembly 
>routine, which would make things much safer.  Email me for the
>procedure if you need it.  -- Kevin

That may not make things safer.  In fact, if not done extremely carefully,
it could be really, really dangerous.  The reason is that if you switch to
an alternate stack then your handler will most likely not be reentrant, and
if it does reenter it trashes its own stack.  I can think of ways to make
handlers which switch stacks reentrant, but they are ugly and complex (How
about storing the state of the stack in a global variable and have all
instructions which affect the stack execute in `critical' sections of code
with interrupts turned off and the global variable gets updated at the same
time.  Sound like fun?  No?  I didn't think so).
--
David Conrad		|	Computer: SYNTAX ERROR.
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"Why not just go mad?"	|			-- Dave Barry
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