Date: Tue, 27 Feb 1996 12:36:26 -0500
From: Andrew Szymkowiak <aes AT rosserv DOT gsfc DOT nasa DOT gov>
Message-Id: <199602271736.MAA06762@rosserv.gsfc.nasa.gov>
To: djgpp AT delorie DOT com
Subject: pctime13 troubles/questions

  When people ask here about interrupts and timer code, they are pointed
to pctime13.zip.  I am trying to use this code with version 2, and have
run into a few problems.

The executable in the zip ("test70.exe") works fine.
When I edit "test70.c" to include "gccint70.h" (it comes
including "tcint70,h", the turbo-c version) and compile
with:
      gcc -g -o test test70.c gccint70.c
The executable GPF's pointing into "_int86". This was using
the v2 release, with CWSDPMI as the server.

Has anyone else seen this, and knows what to change?  I cannot tell
if this code was ever checked with version 2; perhaps it is version 1
specific (though I don't know why).

  I also have a few comments about using this as a pedagogical example:

(1) The subroutine never does anything about locking memory, nor does
the test main set the magic crt0 flags.  It might be good to include
an example of one of the above.

(2) Someone might want to point out that these routines will not allow
really high interrupt rates, since the real mode routine has to perform
two mode switches ( I think). If all one wants to do at interrupt time
is count up the tick counter, wouldn't they be better off to
allocate the tick counter out of DOS memory, and have the real mode
routine increment it directly, and the pm mode routine increment it
using far pointers?  (I will attempt to find time to experiment with
this, but do not feel proficient enough to contribute this yet, since
I think one might have to hand assemble the code for the real mode
interrupt (since the compiler/assembler makes pm code), copy the bytes
into low memory, and hack the interrupt vector to point to it)
 
  -Andy S.