Re: Setting Interrupt mask

Ed Casas (edc@ece.ubc.ca) Mon, 20 Nov 2000 19:38:01 -0800 

Date: Mon, 20 Nov 2000 19:38:01 -0800
From: Ed Casas <edc@ece.ubc.ca>
Subject: Re: Setting Interrupt mask



> I think you need to set(enable) interrupt number 7 in
> the PICs interrupt mask register by 

> 	mov al, 7fh     ;mask everthing except irq7
>       out 21h, al     ;write it to pic

Since you don't know which other interrupts have ISRs active, you
should not alter the state of the other interrupt mask bits.
It's better to do:

	mov	dx,21H
	in	al,dx
	and	al,7FH
	out	dx,al

Exercise: Does this code alter "variables" that could be modified
by different threads?  Should it be put in a critical section?

-- 
Ed Casas   edc@ece.ubc.ca   http://casas.ece.ubc.ca   +1 604 822-2592