Question

V. How does ARM processor differentiate between a timer interrupt and an A/D interrupt?

VI. What does privileged mode mean and what is the major difference between this mode and non-privileged mode?

VII. There are two interrupt pins on ARM microprocessor: IRQ and FIQ. Which one can interrupt the other one and why?

Answer 1

v) In ARM processors if the processor knows what caused the interrupt then, it can jump to a specific location (Adress) where the code is written which can handle the interrupt. The processor can differentiate different interrupts by two ways:

a) If interrupts are numbered then check the number and go to location indicated by vector table(adress specifying the interrupt codes)

b) the processor needs to poll all the possible interrupt sources if the number is not known.

VI) ARM processor works in different modes, we can say in two basic ways privileged and non privileged . User mode is non privileged and all other like IRQ,FIQ etc modes are privileged.

A privileged mode means it is not resticted in accesssing any control register or memory or other resources.

Major difference between privileged and non privileged modes are:

S no.	privileged	non privileged
1	It can access all control registers	It can not access all control registers
2	It has right to access all memory mapped peripheral devices	Restricted access to memory mapped peripheral devices.
3	ex - system mode	User mode

VII) FIQ can interrupt IRQ as FIQ is higher priority interrupt and it can mask IRQ interrupt.