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How does cortex-M33, for example, know previous exception priority?

Susumu Endoh

Hello

I want to know about exception priority.

In following situation

  • A has highest priority, described as priority A.
  • B has medium priority, described as priority B.
  • C has lowest priority, described as priority C.

when following sequence is occurred.

  1. CPU runs in thread mode
  2. Exception C occurs. The CPU enter the handler mode. And the execution priority is priority C.
  3. Exception B occurs. The execution priority is priority B.
  4. Exception A occurs. The execution priority is priority A.
  5. When ISR for Exception A reaches end of task so use EXC_RETURN to return exception.
  6. Now execution back to ISR for B and the execution priority might be priority B.

My Question is how does the Cortex-M33 know correct priority number(priority B in above sequence #6)

Regards,

Susumu

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  • 0 in reply to Robert McNamara

    Robert,

    Thank you for your reply, But I want to clear more.
    In the Exception B handler on priority B, then Exception A occurrs, priority will be Priority A.
    To restore priority B when back from Exception A. Where is location to save Priority-B?

    I Think the saved context which you mentioned is right place to save current priority(Priority-B in above situation).
    But I Could not find out.

    Please show me more details.

    Thanks,
    Susumu

Reply
  • 0 in reply to Robert McNamara

    Robert,

    Thank you for your reply, But I want to clear more.
    In the Exception B handler on priority B, then Exception A occurrs, priority will be Priority A.
    To restore priority B when back from Exception A. Where is location to save Priority-B?

    I Think the saved context which you mentioned is right place to save current priority(Priority-B in above situation).
    But I Could not find out.

    Please show me more details.

    Thanks,
    Susumu

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