Date: Wed, 17 Aug 1994 19:04:46 +0500
From: hvb AT netrix DOT com
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: timer interrupt - help

Dear all,

I'm trying to incorporate a perfomance analyzer (profiler) under
edebug32 of go32. I tried to use the timer interrupt (0x08) at 1000
times a second to get the eip of the current running program.

After installing the interrupt, the timer chip is reprogrammed
so that int 0x08 is called every 1 milisecond. This routine
runs fine until the other program try to access the disk, which
causes the computer to reboot.

Questions:
 1. How can I write the ISR in a way that allows every other
    actions to be processed right?
 2. Is there a way that I can write the ISR directly (without
    the overhead added by _go32_dpmi_...) ?
 3. Is there a better way to call the original int 0x08?
 4. How do I access the stack (to find the eip before the
    interrupt is called.)?

The interrupt routine is as follow:

#define calls_per_tick 55  /* calls per .055 sec. */

static _go32_dpmi_seginfo   rm_old_irq;
static _go32_dpmi_registers rm_regs;
static _go32_dpmi_seginfo   rm_si;
static _go32_dpmi_seginfo   pm_old_irq;
static _go32_dpmi_seginfo   pm_si;
static _go32_dpmi_registers alias_irq_regs;

volatile unsigned int tick_count = calls_per_tick;
/* ------------------------------------------------ */
void
rm_irq_08 ()
{
  asm("cli");

  get_and_analyze_eip (); /* Currently does nothing */

  tick_count--;
  if (tick_count)
  {
    asm("mov  $0x20,%al");
    asm("out  %ax,$0x20");
  }
  else
  {
    alias_irq_regs.x.cs = rm_old_irq.rm_segment;
    alias_irq_regs.x.ip = rm_old_irq.rm_offset;
    alias_irq_regs.x.ss = alias_irq_regs.x.sp = 0;
    _go32_dpmi_simulate_fcall_iret(&alias_irq_regs);
    tick_count = calls_per_tick;
  }
  asm("sti");
}
/* ------------------------------------------------ */
void
pm_irq_08 ()
{
}
/* ------------------------------------------------ */
static int
install_irq ()
{
  int ret;

  rm_si.pm_offset = (int) rm_irq_08;
  pm_si.pm_offset = (int) pm_irq_08;
  pm_si.pm_selector = _go32_my_cs();

  ret = _go32_dpmi_allocate_real_mode_callback_iret(&rm_si, &rm_regs);
  if (ret)
    return 0;

  disable();
  _go32_dpmi_get_real_mode_interrupt_vector(8, &rm_old_irq);
  _go32_dpmi_get_protected_mode_interrupt_vector(8, &pm_old_irq);

  _go32_dpmi_set_real_mode_interrupt_vector(8, &rm_si);
  _go32_dpmi_chain_protected_mode_interrupt_vector(8, &pm_si);
  enable();

  return 1;
}

Hung Bui
Netrix Corporation