Nano100(A)
5.3 Nested Vectored Interrupt Controller (NVIC)
5.3.1 Overview
Cortex-M0 provides an interrupt controller as an integral part of the exception mode, named as
“Nested Vectored Interrupt Controller (NVIC)”. It is closely coupled to the processor kernel and
provides following features:
5.3.2 Features
Nested and Vectored interrupt support
Automatic processor state saving and restoration
Dynamic priority changing
Reduced and deterministic interrupt latency
The NVIC prioritizes and handles all supported exceptions. All exceptions are handled in “Handler
Mode”. This NVIC architecture supports 32 (IRQ[31:0]) discrete interrupts with 4 levels of priority.
All of the interrupts and most of the system exceptions can be configured to different priority
levels. When an interrupt occurs, the NVIC will compare the priority of the new interrupt to the
current running one’s priority. If the priority of the new interrupt is higher than the current one, the
new interrupt handler will override the current handler.
When any interrupts is accepted, the starting address of the interrupt service routine (ISR) is
fetched from a vector table in memory. There is no need to determine which interrupt is accepted
and branch to the starting address of the correlated ISR by software. While the starting address is
fetched, NVIC will also automatically save processor state including the registers “PC, PSR, LR,
R0~R3, R12” to the stack. At the end of the ISR, the NVIC will restore the mentioned registers
from stack and resume the normal execution. Thus it will take less and deterministic time to
process the interrupt request.
The NVIC supports “Tail Chaining” which handles back-to-back interrupts efficiently without the
overhead of states saving and restoration and therefore reduces delay time in switching to
pending ISR at the end of current ISR. The NVIC also supports “Late Arrival” which improves the
efficiency of concurrent ISRs. When a higher priority interrupt request occurs before the current
ISR starts to execute (at the stage of state saving and starting address fetching), the NVIC will
give priority to the higher one without delay penalty. Thus it advances the real-time capability.
For more detailed information, please refer to the “ARM® Cortex™-M0 Technical Reference
Manual” and “ARM® v6-M Architecture Reference Manual”.
Mar 31, 2015
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