/*
* Erase Sector between 'start' and 'end'
* Return:  IAP error code (0 when OK)
* NOTES:  start needs to be a 256 byte boundary
*         size should be 256, 512, 1024 or 4089
*/
unsigned int IAP_erase ()  {
  struct iap_in  iap;                      // IAP input parameters
  unsigned int result[3];                 // IAP results
  unsigned int save_VicInt;                // for saving of interrupt enable register

  save_VicInt = VICIntEnable;              // save interrupt enable status
  VICIntEnClr = 0xFFFFFFFF;                // disable all interrupts
  stop_pll();                              // IAP requires to run without PLL

  iap.cmd = 50;                            // IAP Command: Prepare Sectors for Write
  iap.par[0] = 0;                             // start sector
  iap.par[1] = 27;                           // end sector
  iap_entry (&iap, result);                // call IAP function
  if (result[0])  goto exit;               // an error occured?

  iap.cmd = 52;                            // IAP command: Erase Flash
  iap.par[0] = 0;                             // start sector
  iap.par[1] = 27;                           // end sector
  iap.par[2] = CCLK;                       // CPU clock
  iap_entry (&iap, result);                // call IAP function

exit:

  start_pll();                             // start PLL

  VICIntEnable = save_VicInt;              // enable interrupts
  return (result[0]);
}