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From: Jason Mills <jmills AT cs DOT mun DOT ca>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Timer inside interrupt handler
Date: Sun, 24 Oct 2004 13:05:32 -0230
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Eli Zaretskii wrote:
> How about reading the BIOS tick counter?  That's a simple memory read
> from a fixed address, so it should be safe.  The resolution you get is
> 54 msec.

How exactly? (As you can see I have not had much experience at
low level programming). _bios_timeofday() issues an Int
(according to the sources). I did come across the following on
the newgroup. Does it implement what you suggest?

   #include <go32.h>
   include <sys/farptr.h>

   A variable:

   long tick;

   Convert the real mode segment:offset pair to a linear address offset
   (relative to _dos_ds) like this:

   0x40 * 16 + 0x6c = 0x460

   Use it in the _farpeekl() function like this:

   tick = _farpeekl(_dos_ds, 0x460);

> OTOH, invoking any library functions that may issue Int 21h or other
> real-mode software interrupts is a no-no in an interrupt handler.

Thanks.