writing to a uart

I've got a uart in my SOPC builder system called uart_0 that I'm trying to write to using the serial example, but slightly modified. However the cyg_io_lookup function does not find this uart. I've no idea where to go from here, can someone give me a clue how to access this uart.

static void simple_prog(CYG_ADDRESS data)
{
    cyg_io_handle_t handle;
    Cyg_ErrNo err;
    const char test_string = "serial example is working correctly!\n";
    cyg_uint32 len = strlen(test_string);
    printf("Starting serial example\n");
   // err = cyg_io_lookup( "/dev/haldiag", &handle );
  err = cyg_io_lookup( "/dev/uart_0", &handle );
  printf("error = %d \n",err);
  
    if (ENOERR == err) {
   //     printf("Found /dev/haldiag. Writing string....\n");
          printf("Found /dev/uart_0. Writing string....\n");
        err = cyg_io_write( handle, test_string, &len );
    }
    else {
      printf("Device not detected! \n");    
    }
        
    if (ENOERR == err) {
        printf("I think I wrote the string. Did you see it?\n");
    }
    
    printf("Serial example finished\n");
}