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From: brianc@cognos.UUCP (Brian Campbell)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Dos Calls and Interrupts
Message-ID: <323@cognos.UUCP>
Date: Fri, 23-Jan-87 09:53:28 EST
Article-I.D.: cognos.323
Posted: Fri Jan 23 09:53:28 1987
Date-Received: Sat, 24-Jan-87 09:55:06 EST
References: <216700005@orstcs.UUCP> <115@interlan.UUCP> <1501@cit-vax.Caltech.Edu>
Reply-To: brianc@cognos.UUCP (Brian Campbell)
Organization: Cognos Inc., Ottawa, Canada
Lines: 40
Summary: 

In article <1501@cit-vax.Caltech.Edu> tim@tomcat.caltech.edu (Tim Kay) writes:
>>
>>	Calling DOS from an ISR can be done safely; its tricky, and there
>>	are a number of things to be taken into account.  However, you must
>>	use undocumented DOS calls to do so.
>>
>>  [description of how to do it deleted]
>
>I wonder if a ^C handler could be written that would kill the current
>program even if the program isn't doing any dos calls.
>
>Currently, if you hit ^Break or ^C, a bit is set.  Then when you call
>dos, it checks the bit.  If set, the ^C handler is called, and your
>program (by default) is terminated.  The problem is that many programs
>don't make dos calls, and they can't be killed.  For example, if you
>are running a Turbo Pascal program that gets into an infinite loop,
>you have to reboot the machine.  (I know that there is a {$U+} switch,
>but this makes the program run slower, so I would rather not use it.
>My C compiler doesn't have the equivalent of {$U+}.)
>
>Would it be possible to write a TSR program that notices when ^C is
>hit and sets a bit.
>The next time a clock interrupt happens (as described in the article),
>both this bit and the dirty bit are checked.  If ^C has been hit, and
>it is safe to call dos, then the handler should issue a dos terminate
>call to terminate the interrupted program.

I believe that there is such a TSR utility.  It was presented in one of
the earlier issues of PC-Magazine last year.  I think it was called UNCRASH.
The idea was that hitting Ctrl-Break once would function as always, hitting 
it twice did something further, and hitting it three times would get you out
of just about anything (including a JMP $+0) and terminate the program.  I 
think it was implemented using the keyboard interrupt, but I'm not sure on 
that.

If necessary, I can dig out the issue and either post or email the code
(assuming I'm not breaking any copyrights Ziff-Davis may have).

Brian Campbell