Article View: comp.os.msdos.programmer
Article #4054Re: Interrupt Driven Communication
From: Kent Williams
Date: Fri, 28 Dec 1990 18:39
Date: Fri, 28 Dec 1990 18:39
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1354 bytes
38,400 BPS is too fast on an XT unless you do a hard polling loop in
assembly language.
38,400 BPS = 3,840 CPS (at 8 bits per byte). That means an interrupt
roughly every 275 microseconds. You have roughly one instruction per micro-
second on an XT (and that's being generous). I would estimate you couldn't
do a bare bones interrupt service in under 50 instructions, so you would tie
up the CPU 1/5 of the time in interrupt services for the serial port. Then,
consider how many instructions it takes to effect a task switch from the timer
tick interrupt. What do you get? Missed serial port interrupts!
--
Kent Williams --- williams@umaxc.weeg.uiowa.edu
"'Is this heaven?' --- 'No, this is Iowa'" - from the movie "Field of Dreams"
"This isn't heaven, ... this is Cleveland" - Harry Allard, in "The Stupids Die"
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!ns-mx!umaxc.weeg.uiowa.edu!williams From: williams@umaxc.weeg.uiowa.edu (Kent Williams) Newsgroups: comp.os.msdos.programmer Subject: Re: Interrupt Driven Communication Message-ID: <3746@ns-mx.uiowa.edu> Date: 28 Dec 90 18:39:35 GMT References: <53025@eerie.acsu.Buffalo.EDU> Sender: news@ns-mx.uiowa.edu Reply-To: williams@umaxc.weeg.uiowa.edu.UUCP (Kent Williams) Organization: U of Iowa, Iowa City, IA Lines: 16