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From: cyamamot@kilroy.jpl.nasa.gov (Cliff Yamamoto)
Newsgroups: comp.os.msdos.programmer
Subject: Is _chain_int safe in MSC 5.1?
Summary: Does it pop the stack before calling?
Keywords: interrupts, stack
Message-ID: <1991Feb28.081734.21649@elroy.jpl.nasa.gov>
Date: 28 Feb 91 08:17:34 GMT
Sender: news@elroy.jpl.nasa.gov (Usenet)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 33
Originator: cyamamot@kilroy
Nntp-Posting-Host: kilroy.jpl.nasa.gov

Greetings!

I'm about to redirect some interrupts into some code I'm hooking
onto Int 8 or 1C.  When I comes down to calling the 'savedintvector'
I'd like to call it safely.  Can I just call it or should I call it
through the _chain_int function?

I'm also using _dos_setvect and _dos_getvect which use the Int 21 interface
but I'm still don't understand where a new stack is created for the
interrupt routine.  Since DOS is not reentrant, I know its stack has to be
left alone while the interrupt uses its own stack.  Does _dos_setvect
and _dos_getvect take care of creating and deleting a new stack for me?

The reason I'm wondering whether to use _chain_int or not is because I'm
not sure exactly what it does.  I just don't want to risk clobbering the
DOS stack (which probably isn't very big) if my interrupt routine starts
using the stack heavily.  I don't intend to call any DOS routines in my
interrupt.

BTW. What the heck does the keyword 'interrupt' mean in MSC 5.1?  I can't
     find it described anywhere.  Does this somehow take care of keeping
     the DOS stack in order for me?

Any info or pointers to good literature/PD code would be appreciated.

Regards,
Cliff Yamamoto
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