/* Function pointer for sending a byte through the UART module.  */
static uint32_t send_tx_byte_default(void)
/* Function pointer for sending a byte through the UART module.  */
static uint32_t send_tx_byte_default(void)
{
    uint32_t err_code = app_uart_put(mp_tx_buffer[m_tx_buffer_index]);
    if (err_code == NRF_SUCCESS)
    {
        m_tx_buffer_index++;
    }
    return err_code;
}