From: Eduardo TUDA Lorenzetti Pellini <dochell AT MailAndNews DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Basic IRQ mapping ... What am I doing wrong ?
Date: Fri, 6 Apr 2001 13:42:06 -0400
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Hi friends...

I'm trying to hook a &^@&^#&^ IRQ with my DJGPP program.
I hate to post code on the newsgroup, but i don't have more options.
The program is running over plain DOS (IO.SYS, MSDOS.SYS and COMMAND.COM 
ONLY).
I'm trying to hook IRQ 0 - System Timer Interrupt (0x08) with no sucess.
I can hook INT 0x1C, but i need the real IRQ ISR INT 0x08 
8((
Please, if you have time, take a look to this (minimum) code and tell me 
what 
is wrong. It works for INTERRUPT = 0x1C, but don't for 0x08.
Do i need to hook the real mode 0x08 interrupt ? Or both the protected and 
real mode ones ?

---8<--- cut here ---8<----

#include <stdio.h>
#include <go32.h>
#include <dpmi.h>
#include <pc.h>
#include <unistd.h>

#define INTERRUPT 0x08  //works for INTERRUPT 0x1C

unsigned int ct;
_go32_dpmi_seginfo oldvect;
_go32_dpmi_seginfo newvect;

void hookint(void);
void unhookint(void);

int *newtimer(void)
{
 ct++;
}

int *endtimer(void)
{
}

int main(void)
{
 sound(500);usleep(50000);nosound();
 printf("Hooking INT %X...\n",INTERRUPT);
 ct=0;
 hookint();
 while(ct<=100); //just to wait a few seconds...
 unhookint();
 printf("The End\n");
 sound(900);usleep(50000);nosound();
 return(1);
}

void hookint(void)
{
 _go32_dpmi_lock_code (newtimer, (long)endtimer - (long)newtimer);
 _go32_dpmi_lock_data (&ct,sizeof(ct));
 _go32_dpmi_get_protected_mode_interrupt_vector (INTERRUPT, &oldvect);
 newvect.pm_offset = (long)newtimer;
 newvect.pm_selector= _go32_my_cs();
 _go32_dpmi_allocate_iret_wrapper (&newvect);
 _go32_dpmi_set_protected_mode_interrupt_vector (INTERRUPT, &newvect);
}

void unhookint(void)
{
 _go32_dpmi_set_protected_mode_interrupt_vector (INTERRUPT, &oldvect);
 _go32_dpmi_free_iret_wrapper(&newvect);
}

---8<--- cut here ---8<---

Thanks in advance for your help and attention !!

Eduardo TUDA DocHell Lorenzetti Pellin
PEA - Electrical Energy and Automation Department
USP - Politechnical School of Sao Paulo University - BRAZIL
http://www.pea.usp.br/~epellini
---------------------------------
And if you have a time to loose,
an open mind, and right to choose,
would you care to take a look,
or can you read me like a book...
time's is allways on my side...
--------------------------------- (Up the Irons !!!)