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From: stevens@vms.macc.wisc.edu (PAul STevens -- MACC)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: IBM PC Convertible Keyboard Question
Message-ID: <1991Jun5.004702.22218@macc.wisc.edu>
Date: 5 Jun 91 00:32:11 GMT
Sender: news@macc.wisc.edu (USENET News System)
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Organization: University of Wisconsin Academic Computing Center
Lines: 19

I have a more-or-less realtime application that will just barely keep
up with the world on a Convertible.  But I have what seems to be a 
problem with the keyboard interrupt.  I replace the keyboard interrupt
vector (at address 00:24h) and receive interrupts very nicely.  But
it appears that the interrupt itself requires about one millisecond!
At the interrupt address:
        push ax
 	in   al,21h
        or   al,2   ; disable keyboard
        out  21h,al
        mov  al,20h
        out  20h,al  ; reenable interrupt chip
        sti
        nop
It seems that it takes about one millisecond to get to the nop when a
keyboard interupt occurs.  What is going on??????  Is the keyboard actually
causing some other interrupt which is then passed on to me
after some thrashing about?  I cannot afford to spend one millisecond with
interrupts locked out.