From:	AYeryomin AT excelsior-usa DOT com (Alex Yeryomin)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Hardware Interrupt Latency in Protected Mode?
Date:	14 Jul 2003 23:55:52 -0700
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To:	djgpp AT delorie DOT com
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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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