if (DISK_DELAY) {
  extern int disk_interrupt_delay;
  if (disk_interrupt_delay) {
    if (--disk_interrupt_delay == 0) {
      disk_throw_interrupt(); }}}

if (trace_pt &&
    p0_pc == trace_pt &&
    trace == 0 &&
    prom_enabled_flag == 0) {
  if (trace_pt_count) {
    if (--trace_pt_count == 0)
      trace = 1; }
  else { trace = 1; }
  if (trace) printf("trace on\n"); }

/*
 * map virtual address to physical address,
 * possibly returning l1 mapping
 * possibly returning offset into page
 */
inline unsigned int map_vtop(unsigned int virt, int *pl1_map, int *poffset) {
  int l1_index, l2_index, l1;
  unsigned int l2;
  /* 24 bit address */
  virt &= 077777777;
  /* frame buffer */
  if ((virt & 077700000) == 077000000) {
    /*  077000000, size = 210560(8) */
    if (virt >= 077051757 && virt <= 077051763) {
      traceio("disk run light\n"); }
    else {
      if (0) traceio("tv: frame buffer %o\n", virt); }
    if (poffset)
      *poffset = virt & 0377;
    return (1 << 22) | (1 << 23) | 036000; }
  /* color */
  if ((virt & 077700000) == 077200000) {
    if (poffset)
      *poffset = virt & 0377;
    return (1 << 22) | (1 << 23) | 036000; }
  /* this should be move below - I'm not sure it has to happen anymore */
  if ((virt & 077777400) == 077377400) {
    if (0) traceio("forcing xbus mapping for disk\n");
    if (poffset)
      *poffset = virt & 0377;
    return (1 << 22) | (1 << 23) | 036777; }
  /*
    764000-7641777 i/o board
    764140 chaos (77772060)
  */
  /* 11 bit l1 index */
  l1_index = (virt >> 13) & 03777;
  l1 = l1_map[l1_index] & 037;
  if (pl1_map)
    *pl1_map = l1;
  /* 10 bit l2 index */
  l2_index = (l1 << 5) | ((virt >> 8) & 037);
  l2 = l2_map[l2_index];
  if (poffset)
    *poffset = virt & 0377;
  last_virt = virt & 0xffffff00;
  last_l1 = l1;
  last_l2 = l2;
  if ((virt & 0077777000) == 0076776000) {
    printf("vtop: pdl? %011o l1 %d %011o l2 %d %011o\n",
           virt, l1_index, l1, l2_index, l2); }
  return l2; }