UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 20 December 2013 746 of 841
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 user guide
34.3.3 Exception model
This section describes the exception model.
34.3.3.1 Exception states
Each exception is in one of the following states:
• Inactive
The exception is not active and not pending.
• Pending
The exception is waiting to be serviced by the processor.
An interrupt request from a peripheral or from software can change the state of the
corresponding interrupt to pending.
• Active
An exception that is being serviced by the processor but has not completed.
Remark: An exception handler can interrupt the execution of another exception
handler. In this case both exceptions are in the active state.
• Active and pending
The exception is being serviced by the processor and there is a pending exception
from the same source.
34.3.3.2 Exception types
The exception types are:
• Reset
Reset is invoked on power up or a warm reset. The exception model treats reset as a
special form of exception. When reset is asserted, the operation of the processor
stops, potentially at any point in an instruction. When reset is deasserted, execution
restarts from the address provided by the reset entry in the vector table. Execution
restarts as privileged execution in Thread mode.
• NMI
A NonMaskable Interrupt (NMI) can be signalled by a peripheral or triggered by
software. This is the highest priority exception other than reset. It is permanently
enabled and has a fixed priority of -2. NMIs cannot be:
– masked or prevented from activation by any other exception
– preempted by any exception other than Reset.
• Hard fault
A hard fault is an exception that occurs because of an error during exception
processing, or because an exception cannot be managed by any other exception
mechanism. Hard faults have a fixed priority of -1, meaning they have higher priority
than any exception with configurable priority.
• Memory management fault
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