• State Accepted Answer
  • Locked Locked
  • Replies 4 replies
  • Subscribers 350 subscribers
  • Views 2787 views
  • Users 0 members are here
Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

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

Parents
  • +1 in reply to Susumu Endoh

    The "Current Exception Number" is in the xPSR (Special Purpose Program Status Register)

    When there is a new exception taken, this is one of the registers that is saved on the stack.  On Return, this register is "restored".  The Exception Number restored indicates which priority should also be "restored"

Reply
  • +1 in reply to Susumu Endoh

    The "Current Exception Number" is in the xPSR (Special Purpose Program Status Register)

    When there is a new exception taken, this is one of the registers that is saved on the stack.  On Return, this register is "restored".  The Exception Number restored indicates which priority should also be "restored"

Children