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From: rkl@cbnewsh.att.com (kevin.laux)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Accurate timing request
Message-ID: <1991Mar15.135016.25325@cbnewsh.att.com>
Date: 15 Mar 91 13:50:16 GMT
References: <1991Mar6.145414.8747@uwovax.uwo.ca> <1991Mar14.202729.7884@qualcomm.com>
Distribution: na
Organization: AT&T Bell Laboratories
Lines: 41

In article <1991Mar14.202729.7884@qualcomm.com>, rdippold@maui.qualcomm.com (Ron Dippold) writes:
> In article <1991Mar14.040625.13212@comp.vuw.ac.nz> Timothy.Litton@comp.vuw.ac.nz (Tim Litton) writes:
	<clock tick debate deleted>

	I've been following this thread for a bit.  At this time I'd like
to point out that for AT's and most PS/2's with a Real-time clock there are
two services available for timing.  They are Int 15h Function 83h and 86h,
Event Wait and Delay, respectively.  Event Wait will set the high order bit
in a byte flag when the interval expires, while Delay will pause until the
interval expires.  The timing is accurate to 976 microseconds but with
Int 70h it's more like 1 millisecond.

	Event Wait

	AH:	83h
	AL:	00h	Set Interval
		01h	Cancel Interval
	CX:		High order microseconds word
	DX:		Low order microseconds word
	ES:BX		Pointer to flag byte that gets high order bit set
			as soon as possible after end of interval

	Carry Flag clear if successful
	Carry Flag set if error	(Timer already running / function not supported)
	AL:	80h	PC
		86h	XT, AT

	Delay

	AH:	86h
	CX:		High order microseconds word
	DX:		Low order microseconds word

	Carry Flag clear if successful
	Carry Flag set if error	(Timer already running / function not supported)

-- 
________________________________________________________________________________
	R. Kevin Laux				Email: rkl1@hound.att.com
	AT&T Bell Labs				Voice: (908) 949-1160
	Holmdel, NJ 07733			Fax:   (908) 949-0959