ensc254-lab4

.global asm_main

asm_main:

    ;@ Address of LEDs (write to toggle?)
    LDR R0, =0x41210000
    ;@ Address of buttons (read)
    LDR R1, =0x41200000
    ;@ Address of toggle switches (read)
    LDR R2, =0x41220000

    ;@ Values needed to turn light on/off?
    MOV R11, #1 ;@ ON
    MOV R12, #0 ;@ OFF

    ;@ Loop constants. R13 is the length of each cycle. (change to 2 different registers, on/off, for the duty cycle)
    MOV R13, #10

    ;@ Turn LED on.
    _toggleon:
        ;@ *** how do we switch the light on? do that here, somehow
        STR R11, [R0]

        ;@ R3 is used to count down
        MOV R3, R13
        MOV R5, #1 ;@ indicate that light is currently ON
        B _loop

    ;@ Turn LED off.
    _toggleoff:
        ;@ *** how do we switch the light off?
        STR R12, [R0]

        ;@ Set counter to time the loop
        MOV R3, R13
        MOV R5, #0 ;@ indicate that the light is currently OFF.

    ;@ Loop until the counter expires.
    ;@ We also check the buttons & can adjust the loop length, though these changes don't take effect until the next cycle.
    _loop:
        ;@ Check state of BUTTONS to adjust values
        ;@ First read in from the button memory addr.
        LDR R10, [R1]

        ;@ Each bit corresponds to one button; use sequence of AND masks to check each bit
    _checkbutton1:
        ANDS R8, R10, #1
        BEQ _checkbutton2
        ADD R13, R13, #2
    _checkbutton2:
        ANDS R8, R10, #2
        BEQ _checkbutton3
        ADD R13, R13, #20
    ;@ ...etc
    _checkbutton3:

        ;@ Finally, decrement the counter to figure out when the current loop should end.
        SUBS R3, R3, #1
        BNE _loop

    ;@ When the loop ends, decide whether to toggle the light 'on' or 'off'
    MOVS R5, R5
    BEQ _toggleon
    B _toggleoff