Xref:	news2.mv.net comp.os.msdos.djgpp:801
From:	larryb AT comtch DOT iea DOT com (Larry Blanchard)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Timer interrupts
Date:	4 Feb 1996 17:55:04 GMT
Organization:	CompuTech
Lines:	21
Message-ID:	<4f2rto$dbp@krel.iea.com>
References:	<DM41sD DOT GLL AT granite DOT mv DOT net>
NNTP-Posting-Host:	comtch.iea.com
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

James T. Sweeten Jr. (sweeten AT belgarath DOT nwscc DOT sea06 DOT navy DOT mil) wrote:
: 	I have a question concerning the timer interrupt 8.
: What is the difference between the protected mode int8 and the real mode
: int 8?
: 	I need to output a value on a d/a board at specific intervals.  I
: originally did this with borland by installing my own timer interrupt routine.
: I was able to get down to 100 micro second (10khz) resolution.  I am trying to
: do the same thing using djgpp.  I have read the faq and have also gotten
: pctime13.zip (This has milisecond resolution for djgpp).  I modified the
: interrupt routines in pctime13.zip, (gccint8.c), to output the data to the
: d/a board ok but I can't get down to 100 micro second resolution.  With an
: input value of 3000 hz I get a nice 1500 hz square wave.  With a value of 
: 4000 hz it works for a while but then locks the machine up.  Any help would
: be appreciated.
: 	I am using 1.12m4 on a 486/66.

I recently had exactly the same need, tried just what you did (also on a
2/66), and got almost the same results.  Mine sometimes even hung at 3000.
Apparently, the overhead of the DPMI stuff is just too great for high
frequencies.  I gave up on djgpp and did it in real mode.  I can do 20Khz
with no problems.

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