Project-Oberon-BlackBox/BlackBox/Po/Files/MouseP.Lola.txt

MODULE MouseP (
  IN clk, rst: BIT;
  INOUT io: [2] BIT;
  OUT out: [28] BIT);
  (* init mouse cmd F4 (start reporting) with start, parity and stop bits added *)
  CONST InitBuf := $FFFFFDE8;  (* 1...1 1 0 1111 0100 0 *)
  TYPE IOBUF = MODULE (IN I: BIT; OUT O: BIT; INOUT IO: BIT; IN T: BIT) ^;
  REG (clk) x, y: [10] BIT;   (*counters*)
    btns: [3] BIT;
    Q0, Q1, run: BIT;
    shreg: [32] BIT;
  VAR buf0, buf1: IOBUF;
    msclk, msdat: BIT;
    shift, endbit, reply: BIT;
    dx, dy: [10] BIT;
BEGIN
  buf0 (0, msclk, io.0, rst);
  buf1 (0, msdat, io.1, run | shreg.0);
  shift := Q1 & ~Q0;   (*falling edge detector*)
  reply := ~run & ~shreg.11;   (*start bit of echoed initBuf, if response*)
  endbit := run & ~shreg.0;   (*normal packet received*)
  dx := {shreg.5 !2, shreg.7 -> 0'8 : shreg[19:12]};   (*sign + ovfl*)
  dy := {shreg.6 !2, shreg.8 -> 0'8 : shreg[30:23]};   (*sign + ovfl*)
  out := {run, btns, 0'2, y, 0'2, x};

  run := rst & (reply | run);
  Q0 := msclk; Q1 := Q0;
  shreg := ~rst -> InitBuf : (endbit | reply) -> $FFFFFFFF'32 : shift -> {msdat, shreg[31:1]} : shreg;
  x := ~rst -> 0'10 : endbit -> x + dx : x;
  y := ~rst -> 0'10 : endbit -> y + dy : y;
  btns := ~rst -> 0'3 : endbit -> {shreg.1, shreg.3, shreg.2} : btns
END MouseP.