DEFINE_DEVICE_TYPE:  I_subtract
 /* Doc: 2.7 "I-" */
  PORT_LIST( in1, in2, out );

  DEFINE_THREAD:   start_up
   {
    int a, b, c, len;

    while (1)
     {
      RECEIVE( "in1", &a, &len );
      RECEIVE( "in2", &b, &len );
      c = a - b;
      SEND( "out", c, 1 );
     }
   }
  END_DEFINE_THREAD.

END_DEFINE_DEVICE_TYPE.