![Texas Instruments SimpleLink Ethernet MSP432E401Y Technical Reference Manual Download Page 106](http://html1.mh-extra.com/html/texas-instruments/simplelink-ethernet-msp432e401y/simplelink-ethernet-msp432e401y_technical-reference-manual_1095578106.webp)
Exception Model
106
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Cortex
®
-M4F Processor
NOTE:
After a write to clear an interrupt source, several processor cycles may be needed for the
NVIC to identify the interrupt source deassert. Thus if the interrupt clear is done as the last
action in an interrupt handler, it is possible for the interrupt handler to complete while the
NVIC sees the interrupt as still asserted, causing errant re-entry of the interrupt handler. This
situation can be avoided by either clearing the interrupt source at the beginning of the
interrupt handler or by performing a read or write after the write to clear the interrupt source
(and flush the write buffer).
See
for more information on exceptions and interrupts.
1.6.1 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 is being serviced by the processor but has not completed.
NOTE:
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.
1.6.2 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 non-maskable Interrupt (NMI) can be signaled using the NMI signal or triggered by software using
the Interrupt Control and State (INTCTRL) register. This exception has the highest priority other than
reset. NMI is permanently enabled and has a fixed priority of –2. NMIs cannot be masked or prevented
from activation by any other exception or 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
A memory management fault is an exception that occurs because of a memory protection related fault,
including access violation and no match. The MPU or the fixed memory protection constraints
determine this fault, for both instruction and data memory transactions. This fault is used to abort
instruction accesses to Execute Never (XN) memory regions, even if the MPU is disabled.
•
Bus Fault
A bus fault is an exception that occurs because of a memory-related fault for an instruction or data
memory transaction such as a prefetch fault or a memory access fault. This fault can be enabled or
disabled.