Date:	Thu, 19 Dec 2002 22:24:53 +0100
From:	Ewout Boks <kiwanda AT boks DOT com>
Organization:	Boks Embedded Systems
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Newsgroups:	comp.os.msdos.djgpp
Subject:	djgpp hw interrupt seg fault
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

hi,
I am trying to port some generic software to the 80386 and use DJGPP as
the compiler for this.

My problem is this: I am trying to hook onto the timer interrupt and
install a handler that increments a counter and, if necessary, swaps the
stack frame (FYI the generic software is the Micro/C OS-II RTOS by Jean
Labrosse ). So, I read the DJGPP HW Interrupt FAQ and discovered that
the timer interrupt hook is basically a software interrupt (int $0x1c ).
I have two other SW interrupt  handlers in my code and they work fine.

I installed a similar handler for the timer hook (using
_go32_dpmi_set_protected_mode_interrupt_vector() ) and I locked all
variables and code involved using the go32 lock functions. The handler
itself does all the necessary pushing and pooing of registers etc.

When I run the code (on Win NT in a DOS box) I get a segmentation fault
as soon as the handler tries to modify a global variable - data local to
the handler can be manipulated without problems. Also I noticed that the
stack frame seemed different from the other software interrupts.  I have
no idea what is happening. Does anybody know the cause of this or knows
about similar things?


Thanks,


Ewout Boks (kiwanda  <---@---> b . o  . k  . s  .. c . o . m

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