Date: Fri, 11 Nov 1994 08:01:47 -0500 (EST)
From: Long Doan <ldoan1 AT mason1 DOT gmu DOT edu>
Subject: Re: A question about writing interrupt handler in gcc
To: ALAN L HIGHTOWER <alh AT engr DOT engr DOT uark DOT edu>
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu

On Wed, 9 Nov 1994, ALAN L HIGHTOWER wrote:

> I have a handler that catches irqs off a Gravis UltraSound.  My main 
> problem centers around the timer.  Using MSC v6.0, the handler keeps up 
> with the UltraSound perfectly, even all the way up to the GUS's maximum 
> timer resolution of one tic per 80us, or 12500 times a second.  However, 
> using djgpp I hit the max at about 100 times a second.
  
  Look at the fullscreen debugger (fsdb104.zip : oak.oakland.edu 
  /SimTel/msdos/djgpp) The debugger's timer routine was designed to work
(and has been tested with) timer setting at 1ms. 

>     I'm using the dpmi chain pm int vector to establish the handler, 
> and doing nothing more than checking the type of int and calling the 
> appropriate function.  In the timers case, simply incrementing a var.
> As far as the functionality of the handler/irq, it works like a charm, 
> dma transfers are successfully done via an irq driven system, and voice 
> related functions are performed correctly, its just the response of the 
> irq or handler itself really lags.   

  You might want to bypass the _..._chain_interrupt because there is a 
'little' overhead involved.

>     I have also noticed an incredible performance hit when using the 
> outportb instructions to do just about anything.  In the MSC version, a 
> simple function to inb a voices real linear position could be called 
> thousands of times a second and never skip a single address in its 
> reports of where the voice was.  On djgpp, the same code takes a lot 
> longer to execute, and in a continuous loop, jumps speratically like it 
> isn't able to keep up its polling as fast as the same voice was running. 
> I am using cli/sti where needed.  How much of a hit is reasonable to 
> expect?

  Instead of outportb, or whatever, try:
  asm("movl _portnum, %dx");
  asm("movl _value, %al");
  asm("out  %al, %dl");

  Hope that helps,
  Long.

+--------------------------------------------------------+
| Long Doan                        ldoan1 AT mason1 DOT gmu DOT edu |
|                                          ld AT netrix DOT com |
+--------------------------------------------------------+