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What happens if an exception occurs during exception processing (a nested exception)?

April 26, 2017exception happens nested occurs

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What happens if an exception occurs during exception processing (a nested exception)?

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When the CPU enters an exception service routine, the EXC bit in TSR is set to indicate an exception is being processed. If a new exception is recognized while this bit is set, then the reset vector is used when redirecting program execution to service the second exception. In this case, NTSR and NRP are left unchanged. TSR is copied to ITSR and the current PC is copied to IRP. TSR is set to the default exception processing value and the NMIE bit in IER is cleared in this case preventing any further external exceptions. The NTSR, ITSR, IRP, and the NRP can be tested in the users boot code to determine if reset pin initiated reset or a reset caused by a nested exception.