LM3S5P3B Datasheet, PDF (95/1170 Pages) Texas Instruments – Stellaris® LM3S5P3B Microcontroller

Stellaris^® LM3S5P3B Microcontroller
2.5.1
2.5.2
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.
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.
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.
■ Usage Fault. A usage fault is an exception that occurs because of a fault related to instruction
execution, such as:
– An undefined instruction
– An illegal unaligned access
– Invalid state on instruction execution
January 20, 2012
95
Texas Instruments-Production Data