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From: sonny@charybdis.harris-atd.com (Bob Davis)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Backgroup processing (Was Re: DOS idle interrupt (INT28))
Message-ID: <5188@trantor.harris-atd.com>
Date: 5 Jan 91 17:55:23 GMT
References: <5094@trantor.harris-atd.com> <1537@netmbx.UUCP> <1990Dec19.050307.16450@engin.umich.edu> <1991Jan5.043055.17637@bronze.ucs.indiana.edu> <773@csource.oz.au>
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Reply-To: sonny@trantor.harris-atd.com (Bob Davis)
Distribution: comp
Organization: Advanced Technology Dept., Harris ESS, Melbourne, FL
Lines: 28

In article <773@csource.oz.au> david@csource.oz.au (david nugent) writes:
>In <1991Jan5.043055.17637@bronze.ucs.indiana.edu> yawei@bronze.ucs.indiana.edu (mr. yawei) writes:
>
>> If you must use the timer interrupts, appending to int 8 is preferrable 
>> than attaching to int 1Ch.
>
>How so?
>
>Using the timer (hardware) interrupt is guaranteed to cause problems where
>some previously installed TSR or device driver speeds up the timer rate.
>Normally such programs filter those to make any "higher level" timer
>handler receive control at the correct rate.
>
>Also, the PIC is rearmed by the time INT 1cH gets control, so you don't
>have to fiddle around with EOI's at all.  It's an "ideal" place to pop-up.

Are you sure that the PIC is rearmed? I read that hardware interrupts
are still locked out at the time that the 1Ch handler gets control, and
that you can compromise things like interrupt-driven comm programs using the 
serial ports if you dawdle too long in EITHER an INT08 handler or in an INT1C 
handler. [Reference: Dettmann's _DOS Programmer's Reference, 2nd Ed._, p. 512]

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