SAADC oversampling + burst mode on three channel

RE: SAADC oversampling + burst mode on three channel

Kazi Afroza Sultana — Thu, 11 Nov 2021 05:33:47 GMT

Good Luck Jon!

Kazi

RE: SAADC oversampling + burst mode on three channel

JohnCC — Thu, 11 Nov 2021 03:18:28 GMT

Hi Kazi,

Thank you for your support. I will take more time to test this solution.

RE: SAADC oversampling + burst mode on three channel

Kazi Afroza Sultana — Wed, 10 Nov 2021 14:41:19 GMT

Hello Jon,

Thanks for your reply. I have looked at your code. Good job as you are getting output from ADC channel according to the arrangement. You have added PPI channel to trigger START from END event, so that may resolve the issue. It is fine.

It is sometimes a bit hard to say if there is any issue just by looking at the part of code. You can test it and feel free to ask us questions if there are any specific issues.

Best Regards,

Kazi Afroza Sultana

RE: SAADC oversampling + burst mode on three channel

JohnCC — Wed, 10 Nov 2021 05:42:31 GMT

Hi Kazi,

Good news. After i checked this link from you : https://devzone.nordicsemi.com/f/nordic-q-a/20291/offset-in-saadc-samples-with-easy-dma-and-ble/79053#79053 and I used PPI function. I fixed my issue. But I need more time to test it.

I pasted my code and please help me to double check it.(Have any problem in my code?)

I add some PPI init code in below function with my timer init

static void timer_init(void)
{
    uint32_t time_ms = 1; //Time(in miliseconds) between consecutive compare events
    uint32_t err_code;
    uint32_t time_ticks;
  
    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    err_code = nrf_drv_timer_init(&TIMER_PRIXIMITY, &timer_cfg, timer_proximity_event_handler);
    APP_ERROR_CHECK(err_code);
    
    time_ticks = nrf_drv_timer_ms_to_ticks(&TIMER_PRIXIMITY, time_ms);
    nrf_drv_timer_extended_compare(
         &TIMER_PRIXIMITY, NRF_TIMER_CC_CHANNEL0, time_ticks, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, true);
    
    nrf_drv_timer_enable(&TIMER_PRIXIMITY);
    
    uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&TIMER_PRIXIMITY, NRF_TIMER_CC_CHANNEL0);
    uint32_t saadc_sample_event_addr = nrf_drv_saadc_sample_task_get();

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    /* setup ppi channel so that timer compare event is triggering sample task in SAADC */
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel, timer_compare_event_addr, saadc_sample_event_addr);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel0);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_enable(m_ppi_channel0);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel0, nrf_saadc_event_address_get(NRF_SAADC_EVENT_END), nrf_saadc_task_address_get(NRF_SAADC_TASK_START));
    APP_ERROR_CHECK(err_code);
}

And I haven't changed anything else

Thank you.

RE: SAADC oversampling + burst mode on three channel

Kazi Afroza Sultana — Tue, 09 Nov 2021 18:25:15 GMT

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 afterward, 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 on 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

RE: SAADC oversampling + burst mode on three channel

JohnCC — Tue, 09 Nov 2021 03:16:14 GMT

Sorry, I modify the above result

I expected that the arrangement of the data I printed should be 0->1->2

But It is 2->0->1. Why?? Maybe I can use it, but i am confused