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From: dixon@sagittarius.crd.ge.com (walt dixon)
Newsgroups: comp.sys.ibm.pc.programmer,alt.msdos.programmer
Subject: Re: which timer interrupt?
Message-ID: <7352@crdgw1.crd.ge.com>
Date: 3 May 90 18:43:17 GMT
References: <484@wjh12.harvard.edu>
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Organization: General Electric Corp. R&D, Schenectady, NY
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In a previous article David J. Birnbaum writes:

[first two paragraphs deleted]

>Why do some programs hook int 8, while others hook int 1ch?  Is
>there any reason to favor one approach over the other for certain
>applications?  I understand that int 8 operates first, but unless
>you plan to do something that depends on the reading of the system
>clock before int 8 updates it, why would you need to get in that
>early?

A while back I wrote a device driver to generate music on the PC
(using a superset of the BASICA SOUND command).  I needed a higher
resolution timer interrupt than provided by the standard BIOS timer.
I wound up reprogramming the timer to interrupt more frequently (by
a factor of 16).  Every 16th interrupt I called the old int 8 ISR.
Relying on int 1Ch would have resulted in unwanted side effects.

Walt Dixon		{internet:	dixon@crd.ge.com	}
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Walt Dixon dixon@crd.ge.com