Todo: talk about what interrupts are, how to use them, etc...

• Registers

ARM7 Interrupt handler:

 
stmdb	sp!, {r0-r3, r12, lr}
mov	r0, #0x04000000
add	lr, pc, #0x0
ldr	pc, [r0, #-0x4]
ldmia	sp!, {r0-r3, r12, lr}
subs	pc, lr, #0x4

The user ARM7 interrupt vector is thus 0x03FFFFFC (mirrors down into ARM7 work RAM)

ARM9 Interrupt handler:

 
stmdb	sp!, {r0-r3, r12, lr}
mrc	p15, 0, r0, c9, c1	@ r0 = DTCM_BaseAddress + 0x4000
mov	r0, r0, lsr #12
mov	r0, r0, lsl #12
add	r0, r0, #0x4000
add	lr, pc, #0x0
ldr	pc, [r0, #-0x4]		@ bl [DTCM_BaseAddress + 0x3FFC]
ldmia	sp!, {r0-r3, r12, lr}
subs	pc, lr, #0x4

The user ARM9 interrupt vector is thus at DTCM+0x3FFC

In both cases, the BIOS flag word used in swi 0x4 and 0x5 is 4 bytes before the interrupt vector.