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

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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