SAADC oversampling + burst mode on three channel

[JohnCC]

Hi,

    I have two questions as below. Thank you.

1. Oversampling + burst mode only can use on one channel, can't support two or more channel. Is it right?

2. If Q1's answer is yes. How can I average 30 numbers of ADC value on three channel? (for loop 30 times for nrf_drv_saadc_sample() -> is it right?)

for(int i=0;i<30;i++)
{
    err_code = nrf_drv_saadc_sample();
    APP_ERROR_CHECK(err_code); 
    nrf_delay_ms(10);
    v1 = v1 + read buffer[0];
    v2 = v2 + read_buffer[1];
}

v1 = v1/30;
v2 = v2/30;

[Kazi Afroza Sultana]

Hello John,

I think you may either move the call to nrf_drv_saadc_sample() after the printf (for printing the current value of variables) and afterwards can start a new sample; or may wait for the SAADC event even handler to be called before printing to get and print new values. To avoid the potential racing you can try this. 

Though it depends what you want to achieve. If triggering occurs before printf, there may be a race condition since SAADC buffer may or may not be filled with new samples before pritnf is done printing the variables.  

It is recommended to start triggering after offset calibration. If you do offset calibration before starting trigger, the wrong order in the buffer may be caused by this errata: https://infocenter.nordicsemi.com/topic/errata_nRF52832_Rev3/ERR/nRF52832/Rev3/latest/anomaly_832_86.html?cp=4_2_1_0_1_23

You can look at this thread also: https://devzone.nordicsemi.com/f/nordic-q-a/20291/offset-in-saadc-samples-with-easy-dma-and-ble/79053#79053 

Hope it helps.

Best Regards, 

Kazi Afroza Sultana