Setting up IRQ in ARM

Hi everyone

I am new to ARM and really wanted to learn about various aspects of ARM Programming .

I have basic understanding of x86 Assembly.

So,what Specifically I wanted to know is what happens when an external device triggers an interrupt .

Let me put my basic understanding on the same, which I learnt in last few days

Offset Handler
===============
00 Reset
04 Undefined Instruction
08 Supervisor Call (SVC)
0C Prefetch Abort
10 Data Abort
14 (Reserved)
18 Interrupt (IRQ)
1C Fast Interrupt (FIQ)

Whenever Interrupt comes instruction at address 18 is executed

So is it true that it is first instruction executed when interrupts comes??

Or as I read somewhere whenever interrupts comes first it moves from user mode to IRQ mode and cpsr is copied to spsr_IRQ but it happen without an instruction .

After that current instruction is replaced with a blx 0x18

How and where we do need to set the stack for different mode e.g for IRQ mode and Supervisior mode??

In the brancged code

IRQ_HANDLER:

SUB lr, lr, #4

STMFD !sp {r14}

bl IRQ_handler_to_specific_device ;it will branch to actuall hander code.

LDMFD r13!,{r14}
mov pc, r14

Is it all We need to do for setting up Basic IRQ handling ?

Also,how PIC/CPU comes to know that interrupt is coming from which device?

Thanks

Amit Singh Tomar.

"ARM is taking over the world"