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From: everett@hpcvra.CV.HP.COM (Everett Kaser)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Programming the Mouse
Message-ID: <31600001@hpcvra.CV.HP.COM>
Date: 31 Jul 90 19:24:49 GMT
References: <1990Jul30.182430.7493@uokmax.uucp>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 31

/ gene@uokmax.uucp (Gene E. Johannsen) writes...
>	I am writing a program that I want to use the mouse with.  I don't
>have a reference work to the mouse so I am using a list of interrupts.  Below
>is a small program I writing to learn how to use the mouse.  All it will do is
>set up and turn on the mouse and then print an '*' when I press the left
>button.  It prints the '*' but freezes immediately afterwards:

>BUTTON		PROC	FAR
>	push ax		;This is where the problem comes.  It prints 
>	push dx		;the '*' okay, but then it freezes.
>	mov ah,02h	
>	mov dl,2ah
>	int 21h
>	pop dx
>	pop ax
>	ret
>BUTTON		ENDP

I believe that your problem is the call to DOS (INT 21h) inside your mouse
event handler routine.  Since the mouse generates a hardware interrupt, which
controls CPU execution to be vectored to the mouse driver, which then calls
your routine, you cannot call DOS, only manipulate your own code/data space,
make calls to INT 33h (the mouse driver), directly manipulate the display
(dangerous), etc.  Since in your main program you've called DOS to get a key,
when you call DOS from the mouse event handler (which was called from a hard-
ware ISR), you're re-entering DOS.  DOS was not designed to be re-entrant and
you screw up their stacks and flags and stuff.

Everett Kaser                   Hewlett-Packard Company
...hplabs!hp-pcd!everett        work: (503) 750-3569   Corvallis, Oregon
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