Not getting data from adc in continuous mode

[Karthikbss]

I setup my adc in continuous mode with sampling rate set to 200ksps, when I trigger  NRF_SAADC_TASK_START, I am not getting data; unless I trigger NRF_SAADC_TASK_SAMPLE and put a delay after. I am using SDK 16.3

 Is there a way to setup a trigger for adc event done without having to wait using nrf_delay?

ret_code_t err_code;
nrf_saadc_value_t buffer[200];
nrf_saadc_channel_config_t channel_config =
NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);

channel_config.gain = NRF_SAADC_GAIN1_3;
channel_config.acq_time = NRF_SAADC_ACQTIME_3US;
channel_config.mode = NRF_SAADC_MODE_SINGLE_ENDED;

memset(buffer, 0, 200);

nrf_saadc_enable();
nrf_saadc_channel_init(0, &channel_config);
nrf_saadc_buffer_init(buffer, 200);
nrf_saadc_continuous_mode_enable(80);

if(!nrf_saadc_enable_check())
return 1;

nrf_saadc_task_trigger(NRF_SAADC_TASK_START);
while(!nrf_saadc_event_check(NRF_SAADC_EVENT_STARTED));
nrf_saadc_event_clear(NRF_SAADC_EVENT_STARTED);

/*
* Without task trigger task sample and a delay adc does not
* provide data
*/
//nrf_saadc_task_trigger(NRF_SAADC_TASK_SAMPLE);
//nrf_delay_ms(1);

nrf_saadc_task_trigger(NRF_SAADC_TASK_STOP);
while(!nrf_saadc_event_check(NRF_SAADC_EVENT_STOPPED));
nrf_saadc_event_clear(NRF_SAADC_EVENT_STOPPED);

while (!nrf_saadc_event_check(NRF_SAADC_EVENT_END));
nrf_saadc_event_clear(NRF_SAADC_EVENT_END);

#if 1
for (int loop = 0; loop < 200; loop++) {
if ((buffer[loop] > 10) || (buffer[loop] < -10))
{
NRF_LOG_RAW_INFO("%d, %d,\n", loop, buffer[loop]);
NRF_LOG_FLUSH();
}
}
#endif

[Einar Thorsrud]

Hi,

Looking at your code without the call to nrf_delay_ms() you continue to stop sampling immediately after it has been started, so sampling will not have completed. Why are you stopping it?

[Karthikbss]

My intention is to replace nrf_delay_ms call with a function that performs some task, that function could take  less than or greater than one milli second. Once done is there a way to check if adc has completed its task of capturing samples [one set of 200 samples in my case]. Is there a way to avoid having to sleep and check adc status for event done?

I tried to check on "NRF_SAADC_EVENT_END" but that did not work, system would wait for ever on that event.

[Einar Thorsrud]

Hi,

Karthikbss said:

Is there a way to avoid having to sleep and check adc status for event done?

Yes, this is typically handled with interrupts. If you want to run some code when sampling has finished, you should enable an interrupt for that event, and process it in the interrupt/event handler. You can see from the documentation for the SAADC INTEN register that you can enable interrupts for the END event.

[Karthikbss]

Thank you, I got the adc working with status interrupt