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Cortex-M4 interrupt priority dynamically change while in ISR

Adnan Ashraf

Hello,

I am using STM32F407ZGT6 Cortex-M4 microcontroller. I am interested in changing the priority of a certain interrupt while servicing the same interrupt. Is that possible?

More elaborately, lets say I have an interrupt which has a priority of 4. The interrupt has arrived and I am currently in the ISR servicing that interrupt. After running a certain code (in the ISR), I want to run the remaining code (in the ISR) to run at higher priority (say 2). And when I was about to leave the ISR, I again change its priority to 4. Is this possible?

Currently, I have achieved this by calling a higher priority interrupt inside the lower priority interrupt.

Thanking in anticipation for your time and help.

Parents
  • 0 in reply to Adnan Ashraf

    > BASEPRI / PRIMASK registers prevent other low priority exceptions. I don't think, they will be useful in my case.

    Wouldn't changing the priority also prevent other low priority exceptions as well ?

    As far as I understood it, this is how the priority mechanism actually works (but I may be wrong).

    Have you tried ...

    IRQHandler_4

    {

       Code A

       dump contents of BASEPRI

       execute SVC, which has priority 2

       dump contents of BASEPRI

    }

    SVC

    {

    dump contents of BASEPRI

    }

    ... (try making a short test-program, which does nothing except from the above and trigger IRQHandler_4 once only.

    -So using __set_BASEPRI(priority) for setting / restoring it inside the interrupt would have the same effect; you should not have to call/trigger a higher priority interrupt manually.

Reply
  • 0 in reply to Adnan Ashraf

    > BASEPRI / PRIMASK registers prevent other low priority exceptions. I don't think, they will be useful in my case.

    Wouldn't changing the priority also prevent other low priority exceptions as well ?

    As far as I understood it, this is how the priority mechanism actually works (but I may be wrong).

    Have you tried ...

    IRQHandler_4

    {

       Code A

       dump contents of BASEPRI

       execute SVC, which has priority 2

       dump contents of BASEPRI

    }

    SVC

    {

    dump contents of BASEPRI

    }

    ... (try making a short test-program, which does nothing except from the above and trigger IRQHandler_4 once only.

    -So using __set_BASEPRI(priority) for setting / restoring it inside the interrupt would have the same effect; you should not have to call/trigger a higher priority interrupt manually.

Children
  • 0 in reply to Jens Bauer

    Thanks for the reply!

    I am still unable to understand why I need to use BASEPRI. Because SVC has a priority higher than IRQHanlder_4, so the SVC interrupt will easily pre-empt the IRQHandler_4 and I don't need to change BASEPRI. Please correct me if I am wrong.

    Any ways, the idea of using SVC is as similar as I am already achieving by calling a higher priority (software) interrupt inside IRQHandler_4. Please correct me if I am wrong.

    Many thanks for your time and help!