M052LDN Datasheet, PDF (31/86 Pages) List of Unclassifed Manufacturers – 32-bit Microcontroller

M051 DN/DE
6.2.7 Nested Vectored Interrupt Controller (NVIC)
The Cortex^® -M0 provides an interrupt controller as an integral part of the exception mode, named
as “Nested Vectored Interrupt Controller (NVIC)”, which is closely coupled to the processor core
and provides following features:
 Nested and Vectored interrupt support
 Automatic processor state saving and restoration
 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 an interrupt 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”.
6.2.7.1 Exception Model and System Interrupt Map
The following table lists the exception model supported by NuMicro^® M051 DN/DE series.
Software can set four levels of priority on some of these exceptions as well as on all interrupts.
The highest user-configurable priority is denoted as “0” and the lowest priority is denoted as “3”.
The default priority of all the user-configurable interrupts is “0”. Note that priority “0” is treated as
the fourth priority on the system, after three system exceptions “Reset”, “NMI” and “Hard Fault”.
Exception Name
Reset
Vector Number
1
Priority
-3
NMI
2
-2
Hard Fault
3
-1
Reserved
4 ~ 10
Reserved
SVCall
11
Configurable
Reserved
12 ~ 13
Reserved
Oct. 05, 2015
Page 31 of 86
Rev 1.03