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From: readdm@walt.cc.utexas.edu (David M. Read)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Programming the Mouse
Message-ID: <34725@ut-emx.UUCP>
Date: 31 Jul 90 05:54:46 GMT
References: <1990Jul30.182430.7493@uokmax.uucp>
Sender: news@ut-emx.UUCP
Reply-To: readdm@walt.cc.utexas.edu (David M. Read)
Organization: UT-Austin / Jerry's Kids
Lines: 35

In article [abridged] 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:
!>
!>.MODEL	SMALL
!>
!>.CODE
!>
!>  [...]
!>
!>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
!>
!>	END
>
I may be wrong here, but shouldn't this be an 'iret' instruction?  After
all, the routine *is* an interrupt service routine, called by a hardware
interrupt...If you return with a regular 'ret' call, none of the registers
are popped off the stack and restored to their state before the interrupt,
and the CPU doesn't know where to pick up, so it *should* freeze!

-Dave