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4.7. Late-arrival

A late-arriving exception can be handled in preference to a previous exception if the vector fetch has not started and the late-arriving exception has:

  • a higher priority than the previous exception

  • the same priority but a lower exception number than the previous exception.

A late-arriving exception causes a change of vector address fetch and exception prefetch. State saving is not performed for the late-arriving exception because it has already been performed for the initial exception and so does not have to be repeated. In this case, execution commences at the vector of the late arriving exception while the previous exception remains pending.

If a high priority exception is recognized after the vector fetch of the original exception has started, the late-arriving exception cannot use the context already stacked for the original exception. In this case, the original exception handler is pre-empted and its context is saved onto the stack.

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