Look like a bug inside the function nrfx_saadc_calibrate_offset() in SDK 15.3.0 (nRF5_SDK_15.3.0_59ac345)

[Daniel Landry]

m_cb.adc_state is set to NRF_SAADC_STATE_CALIBRATION inside the function nrfx_saadc_calibrate_offset(), but the value is never changed to NRF_SAADC_STATE_IDLE, even is the function return with NRFX_SUCCESS.

Many functions, like nrfx_saadc_channel_init() will return with NRFX_ERROR_BUSY as m_cb.adc_state != NRF_SAADC_STATE_IDLE.

Workaround is to call nrfx_saadc_uninit() that set m_cb.adc_state = NRF_SAADC_STATE_IDLE, and doing a new call to nrfx_saadc_init()

[Simonr]

Hi Daniel

I've reported this internally. It might take a few days to get a reply, but I'll update you when I've gotten a confirmation or explanation on this!

Best regards,

Simon

[Daniel Landry]

Hi Simon,

With some search, I found the solution from https://devzone.nordicsemi.com/f/nordic-q-a/33785/a-plurality-of-a-d-conversion-processing/129869#129869

The application must wait long enough to run the IRQ. nrfx_saadc_irq_handler () sets m_cb.adc_state = NRF_SAADC_STATE_IDLE and calls our own adc_event_handler.

I provide my solution in case it could help someone else. In my application, nrfx_saadc_calibrate_offset() is called once every 30 minutes. nrfx_saadc_uninit() and nrfx_saadc_init() are called in sequence as workaround for the errata 86 https://infocenter.nordicsemi.com/index.jsp?topic=%2Ferrata_nRF52832_Rev2%2FERR%2FnRF52832%2FRev2%2Flatest%2Fanomaly_832_86.html&cp=3_1_1_0_1_23

nrfx_saadc_config_t saadcCfg;

saadcCfg.resolution = NRF_SAADC_RESOLUTION_10BIT;

saadcCfg.oversample = NRF_SAADC_OVERSAMPLE_DISABLED;

saadcCfg.low_power_mode = false;

saadcCfg.interrupt_priority = SAADC_IRQn;

nrfx_saadc_init(&saadcCfg, ub_adc_event_handler);

/*-<ADC offset calibration >-*/
err_code = nrfx_saadc_calibrate_offset();
APP_ERROR_CHECK(err_code);

while (nrfx_saadc_is_busy()) // Wait for calibration to complete

{

    __WFE(); //

    __SEV(); //

    __WFE(); // This sequence puts the system to sleep (SystemON) while waiting

}

// Nordic errata 86 workaround

nrfx_saadc_uninit();

nrfx_saadc_init(&saadcCfg, ub_adc_event_handler);

power_vcc = power_vcc_read();

printf("Vcc: %3d V\n", (int)((power_vcc + 0.005) * 100));

 

/*****************************************************************************/

/**

* \brief      Read the Vcc voltage

*

* \param: none

* \return Vcc

*

*/

float power_vcc_read(void)

{

    nrf_saadc_channel_config_t channelcfg;

    float volt;

    nrf_saadc_value_t ADC_count;

    // Channel configuration

    channelcfg.resistor_p = NRF_SAADC_RESISTOR_DISABLED;

    channelcfg.resistor_n = NRF_SAADC_RESISTOR_DISABLED;

    channelcfg.gain = NRF_SAADC_GAIN1_6;

    channelcfg.reference = NRF_SAADC_REFERENCE_INTERNAL;

    channelcfg.acq_time = SAADC_CH_CONFIG_TACQ_20us;

    channelcfg.mode = NRF_SAADC_MODE_SINGLE_ENDED;

    /* Burst mode used for oversampling */

    if (NRFX_SAADC_CONFIG_OVERSAMPLE != 0)

    {

        channelcfg.burst = NRF_SAADC_BURST_ENABLED;

    }

    else

    {

        channelcfg.burst = NRF_SAADC_BURST_DISABLED;

    }

    channelcfg.pin_p = (SUPPLY_VCC_ADC_PIN + 1); /* NRF_SAADC_INPUT_DISABLED is the value 0 */

    channelcfg.pin_n = NRF_SAADC_INPUT_DISABLED;

    nrfx_saadc_channel_init(0, &channelcfg);

    // ADC conversion

    nrfx_saadc_sample_convert(SUPPLY_VCC_ADC_PIN, &ADC_count);

    /* 3.6 = Internal Reference (0.6V) * 6 */

    volt = 3.6 * ADC_count / cfg.adcmax;

    return (volt);

}

Best regards,

Daniel