From:	atlas_wang AT yahoo DOT com (Wang Yong)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Hardware Interrupt Latency in Protected Mode?
Date:	15 Jul 2003 04:30:39 -0700
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Well, I am doing the same test on a very old industrial PC now, which
has Pentium 90, SiS chipset, ISA Graphic Card, no PCI slot. On board
there has only IDE, 2 serial ports, 1 parallel port, 2 PS/2 (keyboard
and mouse). No network card. OS is FreeDOS. Input is 4KHz square wave
from function generator.

The singals are very stable observed from logical analyzer. Suppose
the time instant of nterrupt singal to IRQ7 is zero. Then the response
of ISR is about 6.x microseonds later, and ISR ends at 9.x
microseconds. And the testing program have been running for about 10
hours.

So, we can make sure that the sudden jitter of interrupt response time
in my previous post is due to hardware (or bios). I'll try to figure
out which part causes this problem. After all, the fact that new
generation of hardware gets bad result is really infrustrating.


Sincerely,
Wang Yong


AYeryomin AT excelsior-usa DOT com (Alex Yeryomin) wrote in message news:<96eb2770 DOT 0307142255 DOT 37239f2f AT posting DOT google DOT com>...
> Dear Wang Yong,
> 
> we have the same problem with real-time program on industrial microPC
> (CPU686E unit, Geode GX1-300MHz processor, onboard flash disk,
> built-in Ethernet10/100 Base-T, from Fastwel / National Semiconductor
> Co).
> 
> In short word, this program gets interrupt 'start' signal from outside
> then runs ADC, gets 'stop' signal and breaks ADC. Depending on ADC's
> samples we culcutale some results. We should be sure that there is no
> delay (or it is very small) between 'start' signal and when ADC runs.
> To catch any delay, we use nanosecond oscillograph. And, as a rule, no
> delay is observed. Really, we found that the delay varies a litte,
> from 5 to 30 mks. Is it OK for us, because we do not disable any
> interrupts and do not re-program Intel 8259 Interrupt Controller, it
> works as is after startup. (By the way, we use 'rdtsc' command to
> measure time intervals with high precision).
> 
> But sometimes we found that the delay is unexpectedly >80 mks! It
> happens in irregular way. We tried to understand but with no success.
> So, we are forced to live with that. :-(
> 
> If you will be more lucky to understand what happens and, more, how to
> fix this problem, please let me know.
> 
> Alex

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