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Tick priority

Posted by Chandra V on July 25, 2009

I wanted to assign proper interrupt priority (not task priority) in interrupt control register for a hardware timer, which is responsible for generating 2HZ system tick as my application need.


Controller : NEC V850
Compiler : IAR
Clk frequency : 2MHZ

My doubt is

Is any other thump rule defined (recommendation) by freeRTOS for system tick handling?
Like a) system tick must not interrupted by any other ISR b) it could be handled in tasks also c) nested interrupt is allowed during execution of tick isr etc.,


RE: Tick priority

Posted by Richard Damon on July 25, 2009
The basic rule is that interrupt that interact with the FreeRTOS kernel (the tick interrupt and any interrupt that calls the FromISR api) should not nest. If your post supports nesting, then interrupts that do not interact with kernel can nest or interrupt ones that do interact. Basically the FromISR routines assume that they are executing inside a critical section of sorts and don't need (or can't) worry about being interrupt in the middle of manipulating critical structures.

RE: Tick priority

Posted by Chandra V on July 25, 2009
Hello Richard,

So, i came to following conclusions based on your input:

1. Unexpected system behavior is expected when an interrupt that interact with the FreeRTOS kernel.
2. freeRTOS kernel delay service won't work in expected manner even if its managed to run.

Thanks a lot for your feedback.


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