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The jitter you see is the differnce in time it takes the RTOS to respond to your IRQ, this is normal. If you want IO lines toggled at very precise time intervals, you need to move the logic into hardware. Nios is just a micro controller, it shouldn't be used to generate clock signals etc.
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I don't understand this point. I thought the irq handler should be indipendent from OS: I expected a jitter in the semaphore pending task but not here.
In this irq handler only deterministic hardware is apparently involved: timer has the highest priority and should be serviced immediately when timer elapses.
I made these hypothesis to explain the behaviour:
- OS uses OS_ENTER/EXIT_CRITICAL macros which sometimes disable IRQs for a while
- OS has an own interrupt dispatcher, so that isr are not called directly
- irq nesting is disabled
At the moment the precision I get is quite enough for my needs, so I didn't verify which one is correct, if any.
However any advice is greatly welcome. Thanks
Regards.
Honored Contributor
