How to handle ARM exceptions and interrupts

       ARM has 7 exceptions: data abort, fast interrupt request, interrupt request, pre-fetch abort, software interrupt, reset and undefined instruction.

       There are two types of interrupts. The first type is caused by peripherals, namely IRQ and FIQ. The second type is a special instruction that causes an interrupt, SWI. Both interrupts will suspend normal program execution.
    
       Exceptions are any situation that requires the normal execution of instructions to be terminated, including reset of the ARM core, failure of instruction fetch or memory access, encountering an undefined instruction, executing a software interrupt instruction, or an external interrupt. Exception handling is the method of dealing with these exceptional situations. Most exceptions correspond to a software exception handler, a software program that is executed when an exception occurs.

       Each exception causes the core to enter a specific mode. Each processor mode has its own set of grouped registers, and the processor mode determines which registers are active and the full read/write access to the cpsr. At the same time, any ARM processor mode can be entered by programmatically changing the cpsr. User and system modes are not entered through exceptions, and can only modify the cpsr.

Exceptions and their modes
Exception Mode Purpose                   
Fast interrupt request FIQ Fast interrupt request processing        
Interrupt request IRQ Interrupt request processing
SWI and reset SVC Protected mode of the operating system
Prefetch abort and data abort abort Virtual memory or memory protection processing
Undefined instruction undefined Software emulation of hardware coprocessor

       An interrupt is a special exception caused by an ARM peripheral. IRQ exceptions are used for normal operating system transaction processing. FIQ exceptions are generally reserved for individual interrupt sources. IRQ can be interrupted by FIQ, but IRQ cannot interrupt FIQ. In order to make FIQ faster, this mode has more shadow registers. FIQ cannot call SWI (software interrupt). FIQ must also disable interrupts.
   

       Each peripheral device has an interrupt line connected to the vectored interrupt controller. The interrupt sources of peripheral functions are generally WDT, timer, UART, I2C, SPI, RTC, A/D, etc. The priority of these interrupts can be set through registers.