Date: Thu, 19 Dec 2002 22:18:23 +0100
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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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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