line example

    .global main
main:
    stmfd sp!, {lr}
    bl clrscr
    mov r1, #10
    mov r2, #10
    mov r3, #75
    mov r4, #85
    mov r11, #2400
    bl lineNoClip
    ldr r4, .KEY_ESC
    bl key_pause
    ldmfd sp!, {pc}

lineNoClip:
    stmfd sp!, {lr}
    mov r7, #1
    subs r5, r3, r1
    rsbmi r5, r5, #0
    rsbmi r7, r7, #0
    mov r8, #1
    subs r6, r4, r2
    rsbpl r6, r6, #0
    rsbmi r8, r8, #0
    add r9, r5, r6
lineloop:
    bl setPixelNoClip
    cmp r1, r3
    cmpeq r2, r4
    beq endlineloop
    add r10, r9, r9
    cmp r10, r6
    addge r9, r9, r6
    addge r1, r1, r7
    cmp r10, r5
    addle r9, r9, r5
    addle r2, r2, r8
    b lineloop
endlineloop:
    ldmfd sp!, {pc}

key_pause:
    stmfd sp!, {lr}
pauseloop:
    mov r0, r4
    bl isKeyPressed
    cmp r0, #0
    beq pauseloop
    ldmfd sp!, {lr}

clrscr:
    stmfd sp!, {lr}
    mov r0, #0xC0000000
    ldr r0, [r0, #0x10]
    mov r1, #0
    mov r2, #0
    mov r11, #0
clrscrloop:
    bl setPixelNoClip
    add r1, r1, #1
    cmp r1, #320
    blt clrscrloop
    mov r1, #0
    add r2, r2, #1
    cmp r2, #240
    blt clrscrloop
    ldmfd sp!, {pc}

setPixel:
    cmp r1, #0
    bxlt lr
    cmp r1, #320
    bxge lr
    cmp r2, #0
    bxlt lr
    cmp r2, #240
    bxge lr
setPixelNoClip:
    stmfd sp!, {r0}
    add r0, r0, r1, lsl #1
    add r0, r0, r2, lsl #9
    add r0, r0, r2, lsl #7
    strh r11, [r0]
    ldmfd sp!, {r0}
    bx lr

.LK:
    .align 2
.KEY_ESC:
    .word   .LANCHOR0
    .section    .rodata
    .align  2
    .set    .LANCHOR0,. + 0
    .type   KEY_NSPIRE_ESC, %object
    .size   KEY_NSPIRE_ESC, 20
KEY_NSPIRE_ESC:
    .word   28
    .word   128
    .word   28
    .word   128
    .byte   0
    .space  3