@ LED Fun & Stuff

LDR R0, =0x44e000AC     @ Address of CM_PER_CPIO1_CLKCTRL
MOV R1, #0x2                @ Enable value for GPIO1 module
STR R1, [R0]                @ Enable GPIO1 module
LDR R1, =0x4804C000     @ GPIO1 base address
MOV R0, #0x01E00000     @ Toggle pins 21-24 value
STR R0, [R1, #0x190]        @ Clear pins 21-24 of GPIO1
LDR R2, [R1, #0x134]        @ Read GPIO1 OE register
BIC R2, R2, R0              @ Modify value, clearing bits 21-24
STR R2, [R1, #0x134]        @ Write back to OE reg.
LDR R0, =LEDStatus      @ Load state variable.
LEDLoop:
    MOV R2, #0x10000000 @ Some big delay constant
    BL LEDFun               @ Call LED-twiddling function
    SUBS R0, R0, #1     @ Decrement LEDStatus
        MOVEQ R0, #6        @ If LEDStatus = 0, reset to 6
D:  SUBS R2, #1         @ Decrement delay constant
        BNE D               @ Wait in delay loop
    B LEDLoop               @ Return to LED cycle.

LEDFun: STMFD SP!, {R0-R2, LR}  @ Store registers used
    LDR R1, =0x4804C000 @ Load GPIO1 base address.  (Is this necessary?)
    MOVS R0, R0         @ Update flags
        BEQ StateZero   @ If in State Zero, branch to StateZero.
    CMP R0, #6              @ If in State Six,
        BEQ StateSix        @ then branch to StateSix
    CMP R0, #5              @ And so on.
        BEQ StateFive
    CMP R0, #4
        BEQ StateFour
    CMP R0, #3
        BEQ StateThree
    CMP R0, #2
        BEQ StateTwo
    CMP R0, #1
        BEQ StateOne

    @ In these State branches, R0 is loaded with the
    @ pins to be Set, and R2 with the pins to be Cleared.
    @ If R0 = 0, all pins should be Cleared, so R0 is not
    @ updated.  After R0 and R2 are loaded, program branches
    @ to LEDTog, which handles clearing, setting, and exiting.
    StateZero:
        MOV R2, #0x01E00000 @ Clear all value
        B LEDTog
    StateSix:
        MOV R2, #0x00400000 @ Clear LED1 value
        MOV R0, #0x00200000 @ Set LED0 value
        B LEDTog
    StateFive:
        MOV R2, #0x00200000 @ Clear LED0 value
        MOV R0, #0x00400000 @ Set LED1 value
        B LEDTog
    StateFive:
        MOV R2, #0x00200000 @ Clear LED0 value
        MOV R0, #0x00400000 @ Set LED1 value
        B LEDTog
    StateFour:
        MOV R2, #0x00400000 @ Clear LED1 value
        MOV R0, #0x00800000 @ Set LED2 value
        B LEDTog
    StateThree:
        MOV R2, #0x00800000 @ Clear LED2 value
        MOV R0, #0x01000000 @ Set LED3 value
        B LEDTog
    StateTwo:
        MOV R2, #0x01000000 @ Clear LED3 value
        MOV R0, #0x00800000 @ Set LED2 value
        B LEDTog
    StateOne:
        MOV R2, #0x00800000 @ Clear LED2 value
        MOV R0, #0x00400000 @ Set LED1 value
        B LEDTog

    LEDTog:
        STR R2, [R1, #0x190]    @ Clear LEDs indicated by R2
        STR R0, [R1, #0x194]    @ Set LEDs indicated by R0
        LDMFD SP!, {R0-R2, PC}  @ Restore registers, move LR to PC

@ GPIO1 base address: 0x4804C000
@ GPIO1 OutputEnable offset: 0x134
@ GPIO1 ClearDataOut offset: 0x190
@ GPIO1 SetDataOut offset: 0x194
@ For enabling all four outputs, 0x01E0 0000 will toggle bits 21-24.
@ For individual toggling:
@ LED0 (pin 21): 0x0020 0000
@ LED1 (pin 22): 0x0040 0000
@ LED2 (pin 23): 0x0080 0000
@ LED3 (pin 24): 0x0100 0000

.align 2
.data
LEDStatus: .word 6