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From:	"Tim Nicholson" <djgpp AT gizzy DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: DPMI Interrupt latency ?
Date:	Sat, 26 Jan 2002 18:26:48 +0000 (UTC)
Organization:	BT Openworld
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If it helps, I wrote an ISR for the parallel port using just DJGPP and I
found that it worked in DOS mode up to a frequency of about 200Khz. After
with it just failed to keep up. I make that 5000 clocks per iteration.

The CPU was running at 1Ghz and the ISR was a simple counter which sounded
the bell (\007) every 100 000 iterations of the counter.

In Windows, the DOS box caused a protection fault at frequencies above
100Khz, I put that down the virtual machine going t*ts up!

Let me know if you get a really fast routine running as I need to clock in
EPP data using an ISR as fast as possible - 200 kHz is OK but if I can
better it then great! :-)

Tim

"Babu Kalakrishnan" <kala AT sankya DOT com> wrote in message
news:slrna5524i DOT 43o DOT kala AT ganga DOT sankya DOT com...
> Could anyone tell me what is the order of delay (in clocks) required for
> the CWSDPMI server to reflect a hardware interrupt from Real mode to the
> protected mode handler ?
>
> I need to write a Hardware Interrupt handler where latency is very
> critical. Any suggestion regarding which DPMI server would provide me
> the best latency figures would also be welcome. (The application need
> not be portable - and I can specify the environment).
>
> I would have liked to setup a Real mode interrupt handler as well to
> reduce the latency - but the problem is that my Interrupt routine needs
> random access to a 4MB buffer in extended memory. Would it be possible
> to hack the DPMI server source code so that real mode handler can access
> memory above 1MB using 32 bit pointers ? (the Flat mode)- in which case,
> which Descriptor do I need to modify ?
>
> Thanks in advance.
>
> BK
>
>

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