PC386 Clock Tick Driver

Joel Sherrill joel.sherrill at OARcorp.com
Thu Jul 18 14:45:20 UTC 2013

On 7/18/2013 8:27 AM, Tim Cussins wrote:
> Hi SAeeD,
> On 17/07/13 12:19, SAeeD wrote:
>> When I use 10000 us for each tick, there is no problem. But when I use
>> 10 us for each tick, I continuously get "Spurious Interrupt: 7" error.
>> This is while 10 us for each tick on LPC3250 works as expected (No
>> spurious interrupt).
> 10us per system tick seems incredibly low. If your processor is handling
> a tick every 10us, are you sure there's enough cycles left to do
> meaningful work?
That is one big issue.

My recollection is that the "spurious interrupt 7" is associated with the
bit in the first 8259 PIC that has the second one associated with it.
AFAIK under a correct implementation of those cascaded interrupt
controllers, you should never get an interrupt 7.

There are buggy implementations of this but in this case, my guess is
that the clock interrupts are occurring faster than they can be effectively
cleared. Could be nesting interrupts, not clearing before another one, etc.
>> Thanks,
>> SAeeD
> Cheers,
> Tim
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Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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