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From: heintze@grane.enet.dec.com (Siegfried Heintze)
Newsgroups: comp.sys.ibm.pc.hardware,comp.os.msdos.programmer
Subject: How to roll my own Clock service routine and emit tones
Keywords: timers, speaker, tones
Message-ID: <16408@shlump.nac.dec.com>
Date: 16 Oct 90 18:16:31 GMT
Sender: newsdaemon@shlump.nac.dec.com
Reply-To: heintze@grane.enet.dec.com (Siegfried Heintze)
Followup-To: comp.sys.ibm.pc.hardware
Organization: Digital Equipment Corporation
Lines: 40

I have some questions about timers in the IBM PC/AT and its clones.  I wasn't
sure if this is a
hardware or software question.

(1)  What is the name of the chip they use to generate the clock interrupt every
18.2 ms?
(2)  Where can I get documentation on it?
(3)  I would like to establish my own clock interupt service routine that calls
the 
      default clock routine at the appropriate intervals by use of a counter. 
The purpose of
      this is to gain control at intervals with a granularity greater than 18.2
ms.
      (a)   What is the address of the countdown register?
      (b)   How do I read the current value and write a new value to this 
countdown register?
              I suspect I would use some inport and outport instructions.
      (c)   What is the location of the interupt vector element that holds the
address of the clock
              routine?  I would suppose I use one of the MSDOS services to fetch
the old value and
              write the address of my routine.  I don't recal which service this
is, but I remember
              seeing an example of this in the TURBO C++ documentation.

On a slightly different - but possibly related subject:

(4)  How does BORLAND implement their  sound and nosound routines in TC++?  
These routines
       allow you to generate a study tone while other CPU processing is in
progress.
(5)  How would I write a program that emits an uninterupted tone whose pitch is
controlled
       by the vertical position of the mouse on the screen?

                                                                               
Thanks much,

                                                                               
Sieg