RE: nRF52832: how to trigger SAADC sampling externally via PPI event?

ovrebekk — Wed, 16 Nov 2022 14:36:12 GMT

Good to hear that the example was helpful, and thanks for sharing the specifics you needed to change in order to make it work.

Triggering SAMPLE will not invoke START unfortunately, so START has to be called first.

Best regards
Torbjørn

RE: nRF52832: how to trigger SAADC sampling externally via PPI event?

ISH — Wed, 16 Nov 2022 11:21:19 GMT

The link you provided helped, I managed to get the SAADC to perform a conversion on every COMPARE0-event. I shall provide my solution here just to avoid a situation in the future where the link is not usable.

I followed the sample, and was pleased that my approach was quite similar in comparison. The only steps I didn't do with my SAADC code was to use the task START. I was under the impression that when you use task SAMPLE it would trigger START automatically. These are the changes I made to my code to get it working:

mm_saadc.c

#define MM_SAADC_CH_CNT 1

static nrf_saadc_value_t buffer[MM_SAADC_CH_CNT];
static nrfx_saadc_channel_t channels[MM_SAADC_CH_CNT] = {
    NRFX_SAADC_DEFAULT_CHANNEL_SE(NRF_SAADC_INPUT_AIN0, 0),
    //NRFX_SAADC_DEFAULT_CHANNEL_SE(NRF_SAADC_INPUT_AIN1, 1),
};

uint32_t mm_saadc_address_event_started()
{
    return nrf_saadc_event_address_get(NRF_SAADC, NRF_SAADC_EVENT_STARTED);
}

uint32_t mm_saadc_address_task_start()
{
    return nrf_saadc_task_address_get(NRF_SAADC, NRF_SAADC_TASK_START);
}

static void event_handler(nrfx_saadc_evt_t const * p_event)
{
    nrfx_err_t err;
    switch (p_event->type)
    {
        case NRFX_SAADC_EVT_DONE:
            for (int i = 0; i < p_event->data.done.size; i++) {
                LOG_INF("CH%d: %d", i, p_event->data.done.p_buffer[i]);
            }
            err = nrfx_saadc_buffer_set(&buffer[0], MM_SAADC_CH_CNT);
            break;
/*
        case NRFX_SAADC_EVT_BUF_REQ:
            LOG_INF("NRFX_SAADC_EVT_BUF_REQ");
            err = nrfx_saadc_buffer_set(&buffer[next_free_buf_index()], MM_SAADC_CH_CNT);
            LOG_INF("NRFX_SAADC_EVT_BUF_REQ err: %x", err);
            break;
*/
        case NRFX_SAADC_EVT_READY:
            LOG_INF("Stopping SAADC");
            nrf_saadc_task_trigger(NRF_SAADC, NRF_SAADC_TASK_STOP);
            break;
        default:
            LOG_INF("default: event type %x", p_event->type);
            break;
    }
}

mm_ppi.c

void mm_ppi_set()
{
    nrfx_err_t err = NRFX_SUCCESS;

    err = nrfx_ppi_channel_alloc(&mm_ppi_ch0);
    err = nrfx_ppi_channel_assign(mm_ppi_ch0, mm_rtc_address_event_comp0(), mm_saadc_address_task_start());
    err = nrfx_ppi_channel_fork_assign(mm_ppi_ch0, mm_rtc_address_task_clear());
    err = nrfx_ppi_channel_enable(mm_ppi_ch0);

    err = nrfx_ppi_channel_alloc(&mm_ppi_ch2);
    err = nrfx_ppi_channel_assign(mm_ppi_ch2, mm_saadc_address_event_started(), mm_saadc_address_task_sample());
    err = nrfx_ppi_channel_enable(mm_ppi_ch2);
}

Further development:

I might need to add more SAADC channels to the project, but as long as the configurations are done correctly, this solution should work with minimal modifications.

Thank you.

RE: nRF52832: how to trigger SAADC sampling externally via PPI event?

ovrebekk — Tue, 15 Nov 2022 13:41:33 GMT

My colleague Jørgen made an example that sounds very similar to what you are doing.

Could you start by taking a look at that and see if you can spot the issue with your own example?
https://github.com/jorhol/NCS-SAADC-samples/tree/main/nrfx_saadc_advanced_nrfx_rtc_ppi/

If you still have questions or concerns after checking out his example just let me know, and I will do my best to help out.

Best regards
Torbjørn