pio_write
retval = pio_write(board, priv, buffer, length, &num_bytes);
retval = pio_write(board, priv, &buffer[*bytes_written], 1, &num_bytes);
retval = pio_write(board, priv, buffer, length, &num_bytes);
retval = pio_write(board, priv, &buffer[*bytes_written], 1, &num_bytes);
ret = pio_write(ctrl);