Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!seismo!vrdxhq!tom
From: tom@vrdxhq.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Masking ints while setting interrupt vectors
Message-ID: <3423@vrdxhq.UUCP>
Date: Wed, 15-Apr-87 18:36:41 EST
Article-I.D.: vrdxhq.3423
Posted: Wed Apr 15 18:36:41 1987
Date-Received: Fri, 17-Apr-87 05:01:08 EST
References: <5523@shemp.UCLA.EDU>
Organization: Verdix Corporation, Chantilly, VA
Lines: 44
Keywords: interrupts, masking
Summary: masking off interrupts


There are two ways to do it.

One way is simply to turn off interrupts and turn them on again ...

      PUSHF
      CLI
      << your code to install vector >>
      POPF


Or, you can mask off the timer interrupt at the 8259 interrupt
controller via ...

      ; get the current mask

      MOV  DL, 021H        ; 21h is mask port in AT
      IN   AH, DL

      ; save current mask

      PUSH AX
      
      ; mask off the timer

      OR   AH, Timer_interrupt   ; i don't know which line it is
 
      ; put new mask to 8259

      OUT  AH, DL

      << insert vector installation code here >>

      ; restore old mask

      POP  AX

      OUT  AH, DL

I'm sure I got some of the operand orders wrong, cause I don't
have any books in front of me, but you get the idea ...

Also, the literal Timer_interrupt should be replaced with 3 or
4 or 2 or whatever the timer interrupt into the 8259 is.