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Mail Archives: djgpp/1997/03/22/17:01:46

From: "Anthony Q. Bachler" <cwhizard AT NOSPAM DOT sockets DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: DJGPP gurus: interrupts wrappers are reentrant ?
Date: 21 Mar 1997 21:59:11 GMT
Organization: Apcad Engineering
Lines: 69
Message-ID: <01bc3638$070ea500$LocalHost@anthonyb>
References: <199703211327 DOT OAA21219 AT math DOT amu DOT edu DOT pl>
NNTP-Posting-Host: 208.16.64.202
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

I have now noticed this behavior in ISR's.  I am getting an error in my
program that causes a fault when the ISR is entered for the second time. 
It works fine the first time and updates the variable "volatile long time;
", but when it tries to do it again 55ms later, it comes up as an invalid
instruction or a segment violation (SETSEGV).


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Mark Habersack <grendel AT hoth DOT amu DOT edu DOT pl> wrote in article
<199703211327 DOT OAA21219 AT math DOT amu DOT edu DOT pl>...
> Once upon a time (on 20 Mar 97 at 14:55) Anthony Q. Bachler said:
> 
> > Try clearing the interupt enable bit of the MSW as one of the first
steps in
> > the ISR.  This will cause the hardware to store any interupts that
occur and
> > execute them when you reenable them.  To disable them use the CLI
assembly
> > instruction.  To reenable them use the STI instruction.  A word of
caution,
> > STI should be immediately followed by an IRET to prevent the problem
you are
> > experienceing.  The problem you are having is that the stack is being
> > corrupted.  When you perform an STI, the processor should hold off
executing
> > any pending interupts until after the next command.  I know for a fact
that
> > it works this way on the 8086-80686.  On a different processor, it may
work
> > differently.  The above details are for the intel CPU's, but the method
is
> > the same for most others.
> This won't work under many DPMI servers (as well as under many, perhaps
all, 
> multitasking environments - WinNT, Linux/DOSEMU, OS/2, OpenDOS
MultiTasker) - 
> they virtualize the interrupts and STI & CLI instructions are emulated by
the 
> underlying software. They have effect only on the current application/VM.

> Several days ago I've posted to this newsgroup a short proggy which makes
the 
> interrupts reentrant. Subject: line of the thread had an ISR string in it
- 
> browse mail archives on http://www.delorie.com/djgpp/ and you should be
able 
> to find the message. If not then e-mail me privately and I'll send you
the 
> code.
> 
> ---------- Visit http://ananke.amu.edu.pl/~grendel ------------
> You're just a waste of time, you're just a babbling face, you're
> just three sick holes that run like sores, you're fucking waste
> you're like a slug on the floor, oh you're usless and ugly and
> useless and ugly, and shiver and shake when I think of how you
> make me hate.
> 

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