nRF52832 SDK14 - SAADC calibration issues

RE: nRF52832 SDK14 - SAADC calibration issues

Jørgen Holmefjord — Mon, 09 Sep 2019 12:31:55 GMT

I'm not sure exactly what you refer to with your question, but there are two erratas related to SAADC with TACQ < 10us that I can see, both with a workaround:

RE: nRF52832 SDK14 - SAADC calibration issues

Franz — Sun, 08 Sep 2019 13:09:48 GMT

Sorry for a reply to an old topic, but I stumbled upon this also, and aborting in the CALIBRATE_DONE callback is a solution to the workaround... for sample times >=10µs. What is a reasonable workaround for 3µs/5µs?

RE: nRF52832 SDK14 - SAADC calibration issues

Jørgen Holmefjord — Thu, 01 Feb 2018 15:47:02 GMT

You are correct, but I answered with my previous comment in mind:

[quote user="joh2"]You need to stop the SAADC after calibration.[/quote]

If you call the abort task during calibration, you will have to wait for the STOPPED event. If you call it after calibration, the state should not be set to IDLE undtil after the STOPPED event is received.

RE: nRF52832 SDK14 - SAADC calibration issues

Andy — Tue, 30 Jan 2018 18:27:51 GMT

@Jorgen Holmefjord, as of SDK 14, nrf_drv_saadc_abort is not sufficient, as it does not wait for the SAADC to become IDLE when in calibration mode. Instead, it just sets the state to IDLE, which is incorrect.

@ndarkness, You should manually loop and wait for the SAADC state to be IDLE like this: while(NRF_SAADC->STATUS == (SAADC_STATUS_STATUS_Busy << SAADC_STATUS_STATUS_Pos));

RE: nRF52832 SDK14 - SAADC calibration issues

Jørgen Holmefjord — Tue, 12 Dec 2017 11:34:51 GMT

The document refers to the peripheral tasks and event registers, i.e. starting the TASKS_STOP task and wait for the EVENTS_STOPPED event. If you are using the SAADC driver in the SDK, you can call nrf_drv_saadc_abort to stop the SAADC.

RE: nRF52832 SDK14 - SAADC calibration issues

ndarkness — Tue, 12 Dec 2017 11:08:26 GMT

@Jorgen Holmefjord, how do you stop exactly the SAADC? I have this issue with SDK12.3 and I don't know what functions to use when that document says STOP->STOPPED. Thanks

RE: nRF52832 SDK14 - SAADC calibration issues

Jørgen Holmefjord — Tue, 31 Oct 2017 15:21:01 GMT

There is an errata on this, PAN-86: SAADC: Triggering START task after offset calibration may write a sample to RAM. You need to stop the SAADC after calibration. I thought this was implemented in the driver, but it does not look like it is. I will check this.

RE: nRF52832 SDK14 - SAADC calibration issues

Sydney — Fri, 27 Oct 2017 20:09:29 GMT

edit: sorry I had trouble getting my code to format here, so I edited the relevant code into the original post. But yes, I am doing the buffer conversion on my two buffers, and then I schedule a call to a function that calls nrf_drv_saadc_sample().

RE: nRF52832 SDK14 - SAADC calibration issues

Jørgen Holmefjord — Fri, 27 Oct 2017 08:59:46 GMT

Are you setting up a buffer for conversion before you call nrf_drv_saadc_sample? Could you post a code snippet of the NRF_DRV_SAADC_EVT_CALIBRATEDONE event handling?

RE: nRF52832 SDK14 - SAADC calibration issues

Sydney — Tue, 24 Oct 2017 17:21:26 GMT

Thanks- this does appear to fix the abort timeout, but now there's another issue that may be related. In my SAADC event handler, on NRF_DRV_SAADC_EVT_CALIBRATEDONE, I schedule an event that will call nrf_drv_saadc_sample() the next time the scheduler is processed. When this scheduled event happens, I can confirm that nrf_drv_saadc_sample() does return NRF_SUCCESS, but then I never get any SAADC events. So the next time my timer expires and wants to call nrf_drv_saadc_sample() again, my code can tell that the last sample request never returned. When this happens I can abort, buffer_convert(), and sample() again and it works. But is there a way to detect that nrf_drv_saadc_sample() isn't going to generate any events even though it returned NRF_SUCCESS?

Also of interest- I noticed if I call nrf_delay_us(100) at the end of my CALIBRATEDONE handler, the problem doesn't happen.

RE: nRF52832 SDK14 - SAADC calibration issues

Jørgen Holmefjord — Tue, 24 Oct 2017 12:35:46 GMT

Hi,

It looks like this issue is related to the low power mode of the SAADC driver, and what events are generated by the NRF_SAADC_TASK_STOP task triggered within nrf_drv_saadc_abort().

From the documentation of nrf_drv_saadc_abort(), the following note is given:

NRF_DRV_SAADC_EVT_DONE event will be generated if there is a conversion in progress. Event will contain number of words in the sample buffer.

A conversion will be in progress when the NRF_SAADC_TASK_START task have been triggered. In nrf_drv_saadc_init() interrupts are enabled for NRF_SAADC_EVENT_END, and NRF_SAADC_EVENT_STARTED when low power mode is used, but not for NRF_SAADC_EVENT_STOPPED. This is not an issue when low power mode is not used, as a call to nrf_drv_saadc_buffer_convert will trigger NRF_SAADC_TASK_START, but for low power mode, NRF_SAADC_TASK_START is first triggered in call to nrf_drv_saadc_sample().

In normal operation mode, the END event will generate an interrupt, and call SAADC_IRQHandler(). The handler will also detect the STOPPED event, and set the state to IDLE. In low power mode, no END event will be generated, and therefor no interrupts either.

The solution to this issue would be to enable interrupt for NRF_SAADC_EVENT_STOPPED,before triggering NRF_SAADC_TASK_STOP. This will also be a better approach for normal operation mode, than relying on the NRF_SAADC_EVENT_END to generate the interruot. This can be achieved with this modified version of nrf_drv_saadc_abort():

void nrf_drv_saadc_abort(void)
{
    if (nrf_drv_saadc_is_busy())
    {    
        nrf_saadc_int_enable(NRF_SAADC_INT_STOPPED);
        nrf_saadc_event_clear(NRF_SAADC_EVENT_STOPPED);
        nrf_saadc_task_trigger(NRF_SAADC_TASK_STOP);

        if (m_cb.adc_state == NRF_SAADC_STATE_CALIBRATION)
        {
            m_cb.adc_state = NRF_SAADC_STATE_IDLE;
        }
        else
        {
            // Wait for ADC being stopped.
            uint32_t timeout = HW_TIMEOUT;

            while ((m_cb.adc_state != NRF_SAADC_STATE_IDLE) && (timeout > 0))
            {
                --timeout;
            }
            ASSERT(timeout > 0);
        }
        
        nrf_saadc_int_disable(NRF_SAADC_INT_STOPPED);

        m_cb.p_buffer           = 0;
        m_cb.p_secondary_buffer = 0;
        NRF_LOG_INFO("Conversion aborted.");
    }
}

I will report this issue internally. Thanks for reporting it!

Best regards,

Jørgen