Type of exception

Types of exceptions include resets, interrupts, and faults.The exception handling is sudden and asynchronous to the execution of the instruction.However, since the only exception is a fault, which is caused by an error condition caused by the execution of the instruction, the fault is basically generated synchronously with the instruction that caused it.However, hardware faults such as bus access errors may occur asynchronously with instructions. The table below shows the types of exceptions.

order of priority
Major exception handling

order of priority

The higher up you go in the table below, the higher your priority will be. The most expensive is the reset.If the Cortex-M3 is reset in any state, it will perform the operations indicated in the reset vector.The priority of the reset is -3.Here, as you may have noticed, the priority order is not 0 being the highest, but -3 being the highest setting.NMI is -2, hard fault is -1, and memory management is 0.

When describing the “NVIC register (See Part 17), the priority of exception handling is indicated by this number.There is a register that can raise the priority order to 0, but it doesn’t become the highest priority, so please don’t be mistaken.In the table, there is a column called “Types of Priorities”.You cannot change the priority order of exception handling that is “fixed” here, but you can change the priority order of The exception handling that is “configurable” can be changed by the register.This is the main function of NVIC (Refer to Part 13), this is the change in interrupt priority described in ②.

Major exception handling

No. 1 to 15 are exceptions caused by Cortex-M3. The exceptions are described in the table.No. 16 to 255 are external exceptions when viewed from Cortex-M3.In other words, it is assigned to interrupt processing of microcomputer peripheral functions such as timers, communication functions (SP, I2C, UART, etc.), analog functions (DAC, ADC, etc.), etc.These exceptions will be assigned by the microcontroller vendor for each on-board peripheral function.

No.	Types of exceptions	order of priority	Types of priorities.	Content
1	reset	-3（Highest）	fixed	reset
2	NMI	-2	fixed	Non-maskable interrupts (unmaskable interrupts)
3	hard fault	-1	fixed	Default (all) faults when priority relationships or other handlers are disabled and cannot be executed.
4	memory management	0	Set the possibility	Access to an MPU violation (MPU inconsistency) or an incorrect location (access violation or mismatch)
5	bus fault	1	configurable	Receiver Error on AHB Interface Prefetch faults, memory access faults, and other address and memory-related faults.
6	Dosage Fault	2	configurable	Exceptions due to program errors For example, executing an undefined instruction or attempting a transition to an incorrect state
7-10	reservation	–	–	—
11	SVCall (Supervisor call)	3	configurable	System Service Call by SVC Instruction
12	debugging monitor	4	setting>possible	Debug monitoring when not in the hold Breakpoints, watchpoints and external debugging
13	reservation	–	–	—
14	PendSV	5	configurable	Pending requests for system services
15	SYSTICK	6	configurable	System Timer Notification
16	external interrupt #0	7	configurable	external interrupt #0
……	…………………	…………………	configurable	…………………
255	external interrupt #239	246	configurable	external interrupt #239