Adding Second SAADC increases sleep current to go greater 380uA

[PeterInStillwater]

SDK 16.0 and SDK 17.0 (tried both versions)

nrf52832

Segger Embedded Studio

Windows 10

When Adding an additional ADC the sleep current increases to greater than 380uA (from one to two).  When I comment out either of the two ADCs (see below) the sleep current returns to less than 2uA.

I've been working on this for several days and have gone through all of the DevZone examples I could find on the subject (perhaps not), enough where I was coming back to the same ticket multiple times.  

Here's the code:

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    ret_code_t err_code;

     uint8_t value[SAADC_SAMPLES_IN_BUFFER*2];

     uint16_t adc_value;

     uint32_t        tempVoltage_u32 = 0 ;

    if (p_event->type == NRF_DRV_SAADC_EVT_DONE) //Capture offset calibration complete event {    

        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAADC_SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);
                        
        for (int i = 0; i < SAADC_SAMPLES_IN_BUFFER; i++)
        {
            adc_value = p_event->data.done.p_buffer[i];
            value[i*2] = adc_value;
            value[(i*2)+1] = adc_value >> 8;

            tempVoltage_u32 += p_event->data.done.p_buffer[i] ;
        }

        m_adc_evt_counter++;

        }
 }

void saadc_init (void){

    ret_code_t err_code;

    nrf_drv_saadc_config_t saadc_config = NRF_DRV_SAADC_DEFAULT_CONFIG;

    saadc_config.resolution     = NRF_SAADC_RESOLUTION_12BIT;
    saadc_config.low_power_mode = true; 

    nrf_saadc_channel_config_t channel_0_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_VDD);

    channel_0_config.resistor_p = NRF_SAADC_RESISTOR_DISABLED;   //Disable pullup resistor on the input pin
    channel_0_config.resistor_n = NRF_SAADC_RESISTOR_DISABLED;   //Disable pulldown resistor on the input pin
    channel_0_config.gain       = NRF_SAADC_GAIN1_6;             //Set input gain to 1/6. The maximum SAADC input voltage is then 0.6V/(1/6)=3.6V. The single ended input range is then 0V-3.6V
    channel_0_config.reference  = NRF_SAADC_REFERENCE_INTERNAL;  //Set internal reference of fixed 0.6 volts
    channel_0_config.acq_time   = NRF_SAADC_ACQTIME_10US ;        //Set acquisition time. Set low acquisition time to enable maximum sampling frequency of 200kHz. Set high acquisition time to allow maximum source resistance up to 800 kohm, see the SAADC electrical specification in the PS.
    channel_0_config.mode       = NRF_SAADC_MODE_SINGLE_ENDED;   //Set SAADC as single ended. This means it will only have the positive pin as input, and the negative pin is shorted to ground (0V) internally.
    channel_0_config.burst      = NRF_SAADC_BURST_ENABLED;
    channel_0_config.pin_p      = NRF_SAADC_INPUT_VDD;//NRF_SAADC_INPUT_AIN0;          //Select the input pin for the channel. AIN0 pin maps to physical pin P0.02.
    channel_0_config.pin_n      = NRF_SAADC_INPUT_DISABLED;      //Since the SAADC is single ended, the negative pin is disabled. The negative pin is shorted to ground internally.




    nrf_saadc_channel_config_t channel_1_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN5);

    channel_1_config.resistor_p = NRF_SAADC_RESISTOR_DISABLED;   //Disable pullup resistor on the input pin
    channel_1_config.resistor_n = NRF_SAADC_RESISTOR_DISABLED;   //Disable pulldown resistor on the input pin
    channel_1_config.gain       = NRF_SAADC_GAIN1_6;             //Set input gain to 1/6. The maximum SAADC input voltage is then 0.6V/(1/6)=3.6V. The single ended input range is then 0V-3.6V
    channel_1_config.reference  = NRF_SAADC_REFERENCE_VDD4;      //Set internal reference of fixed 0.6 volts
    channel_1_config.acq_time   = NRF_SAADC_ACQTIME_10US ;        //Set acquisition time. Set low acquisition time to enable maximum sampling frequency of 200kHz. Set high acquisition time to allow maximum source resistance up to 800 kohm, see the SAADC electrical specification in the PS.
    channel_1_config.mode       = NRF_SAADC_MODE_SINGLE_ENDED;   //Set SAADC as single ended. This means it will only have the positive pin as input, and the negative pin is shorted to ground (0V) internally.
    //channel_1_config.burst      = NRF_SAADC_BURST_ENABLED;
    channel_1_config.burst      = NRF_SAADC_BURST_DISABLED;
    //
    channel_1_config.pin_p      = NRF_SAADC_INPUT_AIN1;          //Select the input pin for the channel. AIN0 pin maps to physical pin P0.02.
    channel_1_config.pin_n      = NRF_SAADC_INPUT_DISABLED;      //Since the SAADC is single ended, the negative pin is disabled. The negative pin is shorted to ground internally.



    err_code = nrf_drv_saadc_init(&saadc_config, saadc_callback);
    APP_ERROR_CHECK(err_code);

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

//Comment out to lower sleep current (next two lines)
    err_code = nrf_drv_saadc_channel_init(0, &channel_0_config);
    APP_ERROR_CHECK(err_code);

// Or
// comment out to lower sleep current (next two lines)
    err_code = nrf_drv_saadc_channel_init(1, &channel_1_config);
    APP_ERROR_CHECK(err_code);

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

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0],SAADC_SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);   
    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1],SAADC_SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);   
}

END

Also - Placing the following code in the call back function the micro resets (so it's not being used): 

        nrf_drv_saadc_uninit();

        NRF_SAADC->INTENCLR = (SAADC_INTENCLR_END_Clear << SAADC_INTENCLR_END_Pos);
        NVIC_ClearPendingIRQ(SAADC_IRQn);

I had hopes for this solution but nrf_drv_saadc_unit() causes a reset.
https://devzone.nordicsemi.com/f/nordic-q-a/65477/multi-channel-saadc-disable-in-nrf52832

Also, even though running:

volatile uint32_t temp1;
    volatile uint32_t temp2;
    volatile uint32_t temp3;

    ret_code_t err_code;

    temp1 = *(volatile uint32_t *)0x40007640ul;
    temp2 = *(volatile uint32_t *)0x40007644ul;
    temp3 = *(volatile uint32_t *)0x40007648ul;

    *(volatile uint32_t *)0x40007FFCul = 0ul; 
    *(volatile uint32_t *)0x40007FFCul; 
    *(volatile uint32_t *)0x40007FFCul = 1ul;

    *(volatile uint32_t *)0x40007640ul = temp1;
    *(volatile uint32_t *)0x40007644ul = temp2;
    *(volatile uint32_t *)0x40007648ul = temp3;


Will drop the current back to ~2uA, I'm only able to re-init one channel ( nrf_drv_saadc_channel_init(1, &channel_1_config) ).

attempting to stop (code directly above) and starting the second ADC causes a reset.

I have no float variables or functions.

In conclusion, all I'm attempting to do is use two ADCs and have low sleep current.

Thank you in advance for your assistance.

Peter

[hmolesworth]

One minor issue is the internal reference consumes power when enabled, but there is no spec for the SAADC. The COMP  spec for that internal bandgap is only 13uA, so may be the same, don't know.

INT_REF Current used by the internal bandgap reference when selected as source for VREF = 13 μA

This is the code I use, you may already have tried this:

    while (0 == nrf_saadc_event_check(NRF_SAADC_EVENT_END) && timeout > 0)
    {
        timeout--;
    }
    nrf_saadc_task_trigger(NRF_SAADC_TASK_STOP);
    nrf_saadc_event_clear(NRF_SAADC_EVENT_STARTED);
    nrf_saadc_event_clear(NRF_SAADC_EVENT_END);
    // Disable command
    nrf_saadc_disable();

Errata 178 could be an issue if trying to disable before the SAADC has finished

[PeterInStillwater]

Thank you for the fast response.  No, I have not yet tried your suggestion, nor have I run across it. 

Two obvious questions:

Is this code placed in the saadc_callback? (I assume so) and what is the timeout value initiated to?

I'll give this a shot tomorrow.

Thanks again!

[hmolesworth]

Ah, no; in fact as a general guide there should be as little as possible in the callbacks as the callbacks are run from within the interrupt handlers.

This code would just be used after ADC sampling was completed before going to sleep. It can be used will polled sampling or interrupt-driven sampling. The timeout depends on sampling details, just make it longer than the normal completion time; it isn't (shouldn't be) needed, I use it as a fail-safe.

[PeterInStillwater]

I suspected as such - but asked as several of the examples I've seen have put nrf_drv_saadc_uninit(); in the call back.

[Carl Richard]

Hi, Peter!

I also want to add there is a known bug in the driver caused by easyDMA being enabled and staying on when sampling for multiple channels. Jørgen has provided a more thorough explanation as well as a workaround demonstrating low power multichannel sampling in this thread. I also attached the his demo below.

3343.saadc_low_power_multichannel_sdk15_3_0.zip

Best regards,
Carl Richard