/* ************************************************************** */
/* ************************************************************** */
/*				HRT PROBE			  */
/* ************************************************************** */ 
/* ************************************************************** */
/* hrt_probe - check that we have a device as the specified address.
 * Assume the memory region is already mapped.
 * The address has to be a virtual address mapped to the device I/O space.
 */
int hrt_probe(unsigned long addr)
{
  unsigned char oldval1, oldval2, oldval3, newval2;
  unsigned int oldaddr;
  
  /* save the old values at the address */
  oldval1 = readb(HRT_CONTROL_REG + addr);
  rmb();
  oldaddr = readw(HRT_Y_LOW_REG + addr);
  rmb();
  
  /* freeze the frame grabbing, immediately */
  writeb(0x5B, HRT_CONTROL_REG + addr);
  wmb();
  
  /* write a new value to the first byte in the first raster/row */
  writew(0, HRT_Y_LOW_REG + addr);
  wmb();
  oldval2 = readb(addr);
  rmb();
  writeb(~oldval2, addr);
  wmb();

  /* write oldval2 to the first byte of the next raster/row */
  writew(1, HRT_Y_LOW_REG + addr);
  wmb();
  oldval3 = readb(addr);
  rmb();
  writeb(oldval2, addr);
  wmb();
  
  /* read the value at the previous raster/row */
  writew(0, HRT_Y_LOW_REG + addr);
  wmb();
  newval2 = readb(addr);
  rmb();
  
  /* restore the old values */
  writeb(oldval2, addr);
  wmb();
  writew(1, HRT_Y_LOW_REG + addr);
  wmb();
  writeb(oldval3, addr);
  wmb();
  writeb(oldaddr, HRT_Y_LOW_REG + addr);
  wmb();
  writeb(oldval1, HRT_CONTROL_REG + addr);
  wmb();
  
  return (newval2 == (unsigned char)~oldval2);
}