UART the best way to exploit the full bandwith of nRF52840 Dongle? Send images with UART?

RE: UART the best way to exploit the full bandwith of nRF52840 Dongle? Send images with UART?

ovrebekk — Fri, 14 Aug 2020 12:26:49 GMT

You welcome 🙂

RE: UART the best way to exploit the full bandwith of nRF52840 Dongle? Send images with UART?

Researcher123 — Thu, 13 Aug 2020 13:40:38 GMT

Hi,

Thanks for the responses and clarifications!

RE: UART the best way to exploit the full bandwith of nRF52840 Dongle? Send images with UART?

ovrebekk — Fri, 07 Aug 2020 12:29:01 GMT

Hi Hugh

It is true that the example is set up to handle ASCII strings, but with some changes to the handler you can make pass through the data more indiscriminately.

As for maximizing throughput this is not really dependent on which services or characteristics are used, as long as the example is set up to utilize larger attributes, long data length (aka data length extension), and the 2M high speed mode when available on the phone side.

It is also important to set up the USB handlers to buffer the data into longer packets, to make the BLE communication more efficient.

Best regards
Torbjørn

RE: UART the best way to exploit the full bandwith of nRF52840 Dongle? Send images with UART?

hmolesworth — Wed, 05 Aug 2020 17:19:44 GMT

Ah, would that be the case <sigh>, but this is a Dongle and I expect it is using the USB uart (if not ignore this post :-) So yes the BLE transmission is just data bytes, but in this case the "uart" is actually USB and the Nordic USB handler helpfully messes up non-ascii data. Look for this line in main.c:

#define ENDLINE_STRING "\r\n"

Here is how it's used:

static void nus_data_handler(ble_nus_evt_t * p_evt)
{
    if (p_evt->type == BLE_NUS_EVT_RX_DATA)
    {
        bsp_board_led_invert(LED_BLE_NUS_RX);
        NRF_LOG_DEBUG("Received data from BLE NUS. Writing data on CDC ACM.");
        NRF_LOG_HEXDUMP_DEBUG(p_evt->params.rx_data.p_data, p_evt->params.rx_data.length);
        memcpy(m_nus_data_array, p_evt->params.rx_data.p_data, p_evt->params.rx_data.length);
        // Add endline characters
        uint16_t length = p_evt->params.rx_data.length;
        if (length + sizeof(ENDLINE_STRING) < BLE_NUS_MAX_DATA_LEN)
        {
            memcpy(m_nus_data_array + length, ENDLINE_STRING, sizeof(ENDLINE_STRING));
            length += sizeof(ENDLINE_STRING);
        }
        // Send data through CDC ACM
        ret_code_t ret = app_usbd_cdc_acm_write(&m_app_cdc_acm,
                                                m_nus_data_array,
                                                length);
        if(ret != NRF_SUCCESS)
        {
            NRF_LOG_INFO("CDC ACM unavailable, data received: %s", m_nus_data_array);
        }
    }
}

.. and here:

        case APP_USBD_CDC_ACM_USER_EVT_RX_DONE:
        {
            ret_code_t ret;
            static uint8_t index = 0;
            index++;
            do
            {
                if ((m_cdc_data_array[index - 1] == '\n') ||
                    (m_cdc_data_array[index - 1] == '\r') ||
                    (index >= (m_ble_nus_max_data_len)))
                {
                    if (index > 1)
                    {
                        bsp_board_led_invert(LED_CDC_ACM_RX);
                        NRF_LOG_DEBUG("Ready to send data over BLE NUS");
                        NRF_LOG_HEXDUMP_DEBUG(m_cdc_data_array, index);
                        do
                        {
                            uint16_t length = (uint16_t)index;
                            if (length + sizeof(ENDLINE_STRING) < BLE_NUS_MAX_DATA_LEN)
                            {
                                memcpy(m_cdc_data_array + length, ENDLINE_STRING, sizeof(ENDLINE_STRING));
                                length += sizeof(ENDLINE_STRING);
                            }

This is in .\examples\peripheral\usbd_ble_uart\main.c

This caught me out a while back; best to remove the end-of-line insertion.

RE: UART the best way to exploit the full bandwith of nRF52840 Dongle? Send images with UART?

awneil — Wed, 05 Aug 2020 16:57:02 GMT

[quote userid="92462" url="~/f/nordic-q-a/64535/uart-the-best-way-to-exploit-the-full-bandwith-of-nrf52840-dongle-send-images-with-uart"]Is it also possible to send/receive images with UART?[/quote]

Yes.

It just send bytes - it neither knows nor cares what those bytes represent