RE: nRF52833 SAADC Transmitting full rate data over UART

Jørgen Holmefjord — Thu, 10 Dec 2020 10:16:50 GMT

Hi,

The logs get dropped because the internal log buffer have been filled before your application is able to process it. There are a few different ways to work around this:

Disable deferred logging, by setting NRF_LOG_DEFERRED to 0 in your sdk_config.h file. Note that this will make logs being processed in-line, which may slow down your application.
Increase the log buffer, by setting NRF_LOG_BUFSIZE in your sdk_config.h file. I still see some logs dropped with your sample rate and buffer size set to 16384 in the SAADC example in SDK 17.0.2, but you can increase it even further if you have enough available RAM

Remove overhead in the logs, for instance by using NRF_LOG_RAW_INFO. This macro will only send the string you input and strip the "<info> app: " part of the log. You can also remove any additional logging that is not required, for instance the "NRF_LOG_INFO("ADC event number: %d", (int)m_adc_evt_counter);" part of the example if you still have this. Here you have a code snipper that will remove the overhead in the SAADC example:

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        ret_code_t err_code;

        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);

        int i;
        //NRF_LOG_INFO("ADC event number: %d", (int)m_adc_evt_counter);

        for (i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            NRF_LOG_RAW_INFO("%d\r\n", p_event->data.done.p_buffer[i]);
        }
        m_adc_evt_counter++;
    }
}

Another option is to use the UART driver directly and send large buffers of raw SAADC samples. This will take a bit more work, but you save some overhead of strings and the usage of the logger module.

Best regards,
Jørgen

RE: nRF52833 SAADC Transmitting full rate data over UART

awneil — Wed, 09 Dec 2020 18:23:32 GMT