millfork/examples/a8/endless_scroll.mfk

const word dlAddr = $3000
const word lms1Addr = $4000
const word lms2Addr = $4060
const word lms3Addr = $40c0

array(byte) dl @ dlAddr = [
  $70,$70,$70,
  $52, @word[lms1Addr],
  $52, @word[lms2Addr],
  $52, @word[lms3Addr],
  $41,lo(dlAddr),hi(dlAddr)
]

noinline asm void wait(byte register(a) f) {
  clc
  adc os_RTCLOK.b2
  .rt_check:
  cmp os_RTCLOK.b2
  bne .rt_check
  rts
}

void main() {
  word lms1 @ dlAddr + 4
  word lms2 @ dlAddr + 7
  word lms3 @ dlAddr + 10
  byte hscroli @ $80, a, b, c
  pointer screeni @ $82

  hscroli = $f
  screeni = lms1Addr

  wait(1)
  os_SDLST = dl.addr

  while true {
    if hscroli == $b {
      a = (pokey_random & 15) + 33
      b = (pokey_random & 15) + 33
      c = (pokey_random & 15) + 33

      screeni[0] = a
      screeni[$60] = b
      screeni[$c0] = c

      screeni[$30] = a
      screeni[$30 + $60] = b
      screeni[$30 + $c0] = c

      lms1 += 1
      lms2 += 1
      lms3 += 1
      screeni += 1

      if lms1 == lms1Addr + $30 {
        lms1 = lms1Addr
        lms2 = lms2Addr
        lms3 = lms3Addr
        screeni = lms1Addr
      }

      hscroli = $f
    }
    antic_hscrol = hscroli
    hscroli -= 1
    wait(1)
  }
}