LM3S3748 Datasheet, PDF (51/753 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S3748 Microcontroller
4 Interrupts
The ARM Cortex-M3 processor and the Nested Vectored Interrupt Controller (NVIC) prioritize and
handle all exceptions. All exceptions are handled in Handler Mode. The processor state is
automatically stored to the stack on an exception, and automatically restored from the stack at the
end of the Interrupt Service Routine (ISR). The vector is fetched in parallel to the state saving, which
enables efficient interrupt entry. The processor supports tail-chaining, which enables back-to-back
interrupts to be performed without the overhead of state saving and restoration.
Table 4-1 on page 51 lists all exception types. Software can set eight priority levels on seven of
these exceptions (system handlers) as well as on 37 interrupts (listed in Table 4-2 on page 52).
Priorities on the system handlers are set with the NVIC System Handler Priority registers. Interrupts
are enabled through the NVIC Interrupt Set Enable register and prioritized with the NVIC Interrupt
Priority registers. You also can group priorities by splitting priority levels into pre-emption priorities
and subpriorities. All of the interrupt registers are described in Chapter 8, “Nested Vectored Interrupt
Controller” in the ARM® Cortex™-M3 Technical Reference Manual.
Internally, the highest user-settable priority (0) is treated as fourth priority, after a Reset, NMI, and
a Hard Fault. Note that 0 is the default priority for all the settable priorities.
If you assign the same priority level to two or more interrupts, their hardware priority (the lower
position number) determines the order in which the processor activates them. For example, if both
GPIO Port A and GPIO Port B are priority level 1, then GPIO Port A has higher priority.
See Chapter 5, “Exceptions” and Chapter 8, “Nested Vectored Interrupt Controller” in the ARM®
Cortex™-M3 Technical Reference Manual for more information on exceptions and interrupts.
Table 4-1. Exception Types
Exception Type
-
Reset
Vector
Number
0
1
Non-Maskable Interrupt
2
(NMI)
Hard Fault
3
Priority^a Description
-
Stack top is loaded from first entry of vector table on reset.
-3 (highest) Invoked on power up and warm reset. On first instruction, drops to lowest
priority (and then is called the base level of activation). This is
asynchronous.
-2
Cannot be stopped or preempted by any exception but reset. This is
asynchronous.
-1
All classes of Fault, when the fault cannot activate due to priority or the
configurable fault handler has been disabled. This is synchronous.
Memory Management
4
settable MPU mismatch, including access violation and no match. This is
synchronous.
Bus Fault
The priority of this exception can be changed.
5
settable Pre-fetch fault, memory access fault, and other address/memory related
faults. This is synchronous when precise and asynchronous when
imprecise.
Usage Fault
-
6
7-10
settable
-
You can enable or disable this fault.
Usage fault, such as undefined instruction executed or illegal state
transition attempt. This is synchronous.
Reserved.
SVCall
Debug Monitor
11
settable System service call with SVC instruction. This is synchronous.
12
settable Debug monitor (when not halting). This is synchronous, but only active
when enabled. It does not activate if lower priority than the current
activation.
April 08, 2008
51
Preliminary