Path: utzoo!attcan!uunet!cs.utexas.edu!yale!cmcl2!adm!news
From: CDCKAB%EMUVM1.BITNET@cunyvm.cuny.edu ( Karl Brendel)
Newsgroups: comp.lang.pascal
Subject: (R)interupt problems
Message-ID: <24565@adm.BRL.MIL>
Date: 20 Sep 90 17:09:56 GMT
Sender: news@adm.BRL.MIL
Lines: 28


In article <9009191305.aa17055@VIM.BRL.MIL>,
  carl david <DAVID%UCONNVM.BITNET@cunyvm.cuny.edu> writes:

>I am trying to write an interupt handler for interupt 9, the keyboard
>interupt, which accepts two keystrokes, swallows the first, and
>processes the second.

>The problem is that when I try to chain from my second) interupt back to
>the original interupt 9 handler, after doing "my thing", some stack
>somewhere appears to be goofed.

Have you considered avoiding reentrancy altogether by setting and
clearing an appropriate flag? When you see the keystroke you want to
swallow, swallow it and set a flag that says "I ate it". Return from the
interrupt. When you see the next keystroke, process it, clear the flag
and return (or chain). When you see any other keystroke, clear the flag
and chain. (By "chain", I mean "pass the interrupt call on to whatever
process you stole the interrupt from".)

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