ISR priority and tick interrupt??

nobody wrote on Monday, January 08, 2007:

I am using STR91x port of FreeRTOS. And have following queries regarding FreeRTOS:

1. The OS tick is a watchdog interrupt with priority 10. Why it is not given highest priority i.e 0?

2. If I am having an ISR with priority greater than the Tick interrupt priority, will the tick interrupt will execute in between of the ISR? How can I ensure that my ISR executes uninterrupted? Also if my ISR is of less priority than tick interrupt, how can I ensure that my ISR executes uninterruted after it gets started?

nobody wrote on Monday, January 08, 2007:

By default and in the examples the interrupts in FreeRTOS are not themselves interruptible.  Nesting cannot occur.  The hardware priority of the interrupt only then has an effect when deciding which interrupt to run first when more than one are asserted at the same time.

You can of coarse enable interrupts from an interrupt if you want to but need to do some twiddles in FreeRTOS (?) to make sure it is handled properly.  The best way is to handle the data from an interrupt in a task where interrupts can remain enabled.  You can then priorities your tasks with great flexibility.  If your interrupt handling tasks are higher priority than other normal tasks then the processing still occurs immediately as the high priority task will run as soon as the interrupt completes.

See my answer just given to

nobody wrote on Tuesday, January 09, 2007:

Thanks for ur answer.

But if interrupts are not interrutible then what will happen if the tick interrupt occurs while some other ISR is running? will tick interrupt be delayed?

nobody wrote on Tuesday, January 09, 2007:

This depends on the hardware you are using but generally the tick will be held pending momentarily while your very short other interrupt is being processed.  Some microseconds.