[time-nuts] PC clock comparison software?

Jack Hudler jack at hudler.org
Wed Dec 20 12:14:30 EST 2006


The Timer/Clock interrupt is IRQ 0 no other interrupt has a higher priority,
therefore this interrupt is rarely missed. If it were missed then interrupts
would have to be turned off longer the 110ms (2 times the clock rate) which is
an enormous amount of time and due no doubt to an improperly written device
driver or faulty motherboard/card.

Having said this; a device driver writer would not have interrupts turned off
for long anyway, this is a bit heavy handed on a system. That's what IRQL are
for.

99.9% of ISR routines are microsecond range. So this is not a source of lost
timer interrupts.

Time is extremely important on a telescope (which why I'm going to try the TAPR
Clock Block when I get time) and I've studied this issue of lost timer
interrupts. I can tell you that they just don't occur even when the system is
loaded to the max. We have a watchdog card in our system to detect just such an
event, it has never triggered (except when you push the test button). 

Jack






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