I am writing an assembly FIQ ISR using GCC complier. I want to change return address in FIQ ISR so that after ISR, it returns to the requested address. the reason for doing that is because i am writing a RTOS.
what are the instruction for ISR return in assembly? is it
SUBS PC, R14, #4
? i know in 8051, noraml function call return is RET, ISR return is RETI.
Look at the assembler output of the compiler to see what instructions that are used by fast and normal interrupt handlers.
Remember that a RTOS doesn't just switch return address - you have to switch to a different stack and make sure that all registers (and other important thread states) gets restored to the values of the other task. That can be quite a lot of hard work, if you are not familiar with the processor instructions.