LM3S8938 Datasheet, PDF (43/550 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S8938 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 43 lists all the exceptions. Software can set eight priority levels on seven of these
exceptions (system handlers) as well as on 34 interrupts (listed in Table 4-2 on page 44).
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 can also group priorities by splitting priority levels into pre-emption priorities
and subpriorities. All 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 the
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.
Note: In Table 4-2 on page 44 interrupts not listed are reserved.
Table 4-1. Exception Types
Exception Type
Position Priority^a Description
-
Reset
Non-Maskable
Interrupt (NMI)
0
-
Stack top is loaded from first entry of vector table on reset.
1
-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
-2
Cannot be stopped or preempted by any exception but reset. This is
asynchronous.
Hard Fault
3
Memory Management
4
-1
settable
An NMI is only producible by software, using the NVIC Interrupt Control
State register.
All classes of Fault, when the fault cannot activate due to priority or the
configurable fault handler has been disabled. This is synchronous.
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
-
SVCall
6
7-10
11
settable
-
settable
You can enable or disable this fault.
Usage fault, such as undefined instruction executed or illegal state
transition attempt. This is synchronous.
Reserved.
System service call with SVC instruction. This is synchronous.
June 14, 2007
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