ARM Intterrupt

arm.s

#I assume here that all the memory addresses are set up correctly. 
    IMPORT    main
    EXPORT    start
start
    ldr    r0,=VICVectAddr0            
    ldr    r1,=irqhan
    str    r1,[r0]     ; associate our interrupt handler with Vectored Interrupt 0

    ldr    r0,=VICVectCtrl0
    mov    r1,#Timer0ChannelNumber+(1<<IRQslot_en)
    str    r1,[r0]     ; make Timer 0 interrupts the source of Vectored Interrupt 0

    ldr    r0,=VICIntEnable
    mov    r1,#Timer0Mask
    str    r1,[r0]     ; enable Timer 0 interrupts to be recognised by the VIC

    ldr    r0,=VICVectAddr
    mov    r1,#0
    str    r1,[r0]     ; remove any pending interrupt (may not be needed)

; Initialise Timer 0
    ldr    r0,=T0TCR
    mov    r1,#TimerCommandReset
    str    r1,[r0]     

    ldr    r0,=T0IR
    mov    r1,#TimerResetAllInterrupts
    str    r1,[r0]     

    ldr    r0,=T0MR0
    ldr    r1,=(#Freq/200)-1     ; 5 ms = 1/200 second
    str    r1,[r0]

    ldr    r0,=T0MCR
    mov    r1,#TimerModeResetAndInterrupt
    str    r1,[r0]

    ldr    r0,=T0TCR
    mov    r1,#TimerCommandRun
    str    r1,[r0]     
#Begin writing code here
;blah
;blah
;blah
STOP    B   STOP
     AREA    InterruptStuff, CODE, READONLY
irqhan    sub    lr,lr,#4
    stmfd    sp!,{r0-r1,lr}    ; the lr will be restored to the pc

    ;
    ;CODE GOES HERE
    ;

    ;Reset interrupt
    ldr    r0,=T0IR
    mov    r1,#TimerResetTimer0Interrupt
    str    r1,[r0]           ; remove MR0 interrupt request from timer

    ldr    r0,=VICVectAddr
    mov    r1,#0
    str    r1,[r0]    ; reset VIC

    ldmfd    sp!,{r0-r1,pc}^    ; return from interrupt, restoring pc from lr