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From: petera@utcsri.UUCP (Smith)
Newsgroups: net.micro.pc
Subject: Re: Interrupts and Microsoft C
Message-ID: <2873@utcsri.UUCP>
Date: Fri, 30-May-86 08:56:44 EDT
Article-I.D.: utcsri.2873
Posted: Fri May 30 08:56:44 1986
Date-Received: Fri, 30-May-86 09:58:02 EDT
References: <674@hou2f.UUCP>
Organization: CSRI, University of Toronto
Lines: 54

> 
> 
> 	I have an interrupt service routine which is linked with
> 	my Microsoft 'C' application program. When the program is started
> 	it installs the pointer to the service routine in the vector table.
> 	As soon as the first interrupt is generated I get a stack overflow 
> 	message on the screen and the system hangs. If I disable the external
> 	interrupt source everything works fine. Sounds like a problem in the 
> 	interrupt service routine.
> 
> 	History:
> 	This service routine is written in assembler and works fine when
> 	linked with compiled MS basic. To link with 'C' I changed it
> 	to assume the _TEXT segment for code and DGROUP for data, bss, and 
> 	stack, as per the Microsoft 'C' manual. I allocated more stack during
> 	the linking phase but that didn't seem to help.
> 
> 	One thing that I'm doing that may be a problem is the way I
> 	install the interrupt vector. Rather than using the get/set interrupt
> 	vector functions in DOS I just poke the segment and offset into the
> 	vector page at address 0x2c (IRQ3). I don't understand why this should 
> 	cause a problem.  I did it this way with the compiled basic version.
> 
> 
> 	Is there anything special I need to do when installing a
> 	interrupt service routine which is  used by a Microsoft 'C'
> 	program. Any comments or code examples would be welcome.
> 
> 
> 					Thank You,
> 				
> 					John Antrosiglio
> 					ATT-Bell Labs
> 					ihnp4!hou2f!jca

       Re: Installing an interrupt service routine in C. 

    Since you are getting a stack overflow what is probably happening is
that the Lattice/Microsoft Compiler is generating stack checking code. Ie
every time a function is entered it compares the stack top pointer with
some maximum value, if it is greater it then aborts with a 'stack overflow'
message. The reason you are getting this is due to the fact that the stack
at the time of the interrupt will not be the same one that the C program
is using, the segment may even be different. It is ok to use this stack,
but only for about 20 or 30 pushes. In any case the C stack checking code
will most of the time catch the fact that the stack top is wrong. There
are two solutions. 1: Disable the stack checking code when you compile
this module or 2: Alter the stack overflow trap routine to do nothing.
Note that when you trap the interrupt in C you cannot do any calls to
read/write/malloc etc because they all result in an INT which will
when it returns, prematurely switch on your interrupts. 

  Peter Ashwood-Smith
  University Of Toronto.