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From: yingda@vms.macc.wisc.edu (Ying-Da Lee)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Help needed with MASM and Interrupts
Message-ID: <1802@uwmacc.UUCP>
Date: Thu, 3-Sep-87 11:23:21 EDT
Article-I.D.: uwmacc.1802
Posted: Thu Sep  3 11:23:21 1987
Date-Received: Sat, 5-Sep-87 10:40:30 EDT
References: <69@sickkids.UUCP>
Sender: news@uwmacc.UUCP
Reply-To: yingda@uwwircs.UUCP (Ying-Da Lee)
Organization: UW-Madison Academic Computer Center
Lines: 32

In article <69@sickkids.UUCP> gw@sickkids.UUCP (CFI/Graham Wilson (977-5450) [RI7921Z]) writes:
>I am writing an interrupt handler and have run into a snag with MASM.
>The solution may be obvious, but I can't seem to figure it out.
>
>The situation is as follows.  The clock tick (IRQ0) has been speeded up
>by a factor of 32, and IRQ0 (INT 8) jumps to my routine.  Every 32 interrupts,
>control passes to the BIOS INT 8 handler when my routine is done.  The
>problem is that I can't figure out how to pass control to the BIOS routine.
>
>I tried saving the offset and segment values from the interrupt table
>before changing to my address.  These values are saved as *CODE SEGMENT*
>variables jmpoff and jmpseg respectively (in that order).  If control
>is to pass through to BIOS, I execute the command:
>
>	jmp	FAR [cs:jmpoff]
>

What you need is

	jmp	dword ptr cs:jmpoff

Alternatively, you could define an additional label, e.g.,

old_int8	equ	dword ptr $
jmpoff		dw	?
jmpseg		dw	?

then a simple

	jmp	cs:old_int8

will do.