Issues in reading analog mic data over SAADC pin of nRF52810.

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

ovrebekk — Thu, 21 Jan 2021 07:54:47 GMT

Hi Manish

The slower the sample rate the larger the relative difference will be, since it is the sleep currents (not the active currents) that is most affected by running a timer.

If you want to compare the two you could always use the app_timer itself to sample the ADC, as long as the frequency is not too large. At 1kHz or lower the app_timer should be able to schedule callbacks fast enough.

Then you can compare the current consumption either when using the app_timer or when using a TIMER module, and see if it is big enough to warrant concern.

Best regards
Torbjørn

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

Manish Kaul — Wed, 20 Jan 2021 08:18:07 GMT

[quote userid="2116" url="~/f/nordic-q-a/70113/issues-in-reading-analog-mic-data-over-saadc-pin-of-nrf52810/290126#290126"]but you can find the cleaned up version here[/quote]

Thank you very much.

[quote userid="2116" url="~/f/nordic-q-a/70113/issues-in-reading-analog-mic-data-over-saadc-pin-of-nrf52810/290126#290126"]Is this not the frequency you need?[/quote]

Yes, still need to sample at 8KHz but that's not the only sample rate I need to work on. Will go as low as 1KHz or even 500Hz as well.

[quote userid="2116" url="~/f/nordic-q-a/70113/issues-in-reading-analog-mic-data-over-saadc-pin-of-nrf52810/290126#290126"] but if you are running the ADC already the difference is unlikely to be that large (unless you want to sample the ADC at a slow rate, then an RTC or the app_timer module is preferred). [/quote]

I see. But I really need to lower current consumption while sampling at the same rate (8KHz) and lower. So I was thinking of using Low power timer (RTC) for ADC. In case I want to confirm how much difference do I get with TIMER vs. RTC (since I do intend to also lower the sample rate as mentioned above), can I use RTC1 (already used by app_timer) by modifying the app_timer.c by, for example, adding a function to it which set's the CC1 register (CC0 used already by app timer) and ties the COMPARE1 register to PPI ? Or any other way you suggest I can use the RTC1 timer to not interrupt the app timer routines in my application and at the same time be able to use it for sampling via PPI ?

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

ovrebekk — Wed, 20 Jan 2021 07:47:54 GMT

Hi Manish

[quote user="Manish Kaul"]I had a quick glance at the code and was curious as to why have you enabled the LFCLK [/quote]

This was a remnant from the original example I based it on. After I shared the example with you I cleaned it up a bit, and asked my colleague to include it in his repository.

It seems he hasn't included it there yet, but you can find the cleaned up version here:

devzone.nordicsemi.com/.../nrfx_5F00_saadc_5F00_continuous_5F00_sampling_5F00_v2.zip

[quote user="Manish Kaul"]Can you please explain me how I can use a separate RTC module to trigger ADC sample (using PPI only) given that nRF52810 has only RTC0(used by softdevice) and RTC1(used by app_timer) ?[/quote]

There is no need to use a separate timer if you want to sample at 8kHz, then you can use the SAMPLERATE register as the example shows. Is this not the frequency you need?

If you don't have any RTC's available you can also use a TIMER module to trigger ADC sampling. Generally the TIMER modules use more current than RTC's (while offering better accuracy), but if you are running the ADC already the difference is unlikely to be that large (unless you want to sample the ADC at a slow rate, then an RTC or the app_timer module is preferred).

Best regards
Torbjørn

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

Manish Kaul — Tue, 19 Jan 2021 11:12:37 GMT

Thanks overbekk, for the example. I had a quick glance at the code and was curious as to why have you enabled the LFCLK ? Wouldn't the internal ADC timer use the HFCLK(16MHz) ?
Also,

[quote userid="2116" url="~/f/nordic-q-a/70113/issues-in-reading-analog-mic-data-over-saadc-pin-of-nrf52810/287651#287651"]For triggering ADC samples it is recommended to use a separate TIMER or RTC module[/quote]

Can you please explain me how I can use a separate RTC module to trigger ADC sample (using PPI only) given that nRF52810 has only RTC0(used by softdevice) and RTC1(used by app_timer) ?

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

ovrebekk — Mon, 18 Jan 2021 14:14:13 GMT

Hi Manish

You will find the example attached:

devzone.nordicsemi.com/.../nrfx_5F00_saadc_5F00_continuous_5F00_sampling.zip

It is based on a set of ADC examples made by one of my colleagues, but adjusted to use the SAMPLERATE feature.

Best regards
Torbjørn

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

Manish Kaul — Thu, 14 Jan 2021 08:02:15 GMT

Hey,

Sure and please do share your entire code with me . Thanks !

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

ovrebekk — Thu, 14 Jan 2021 08:00:39 GMT

Hi Manish

I will try to set up a small example to get this working, and see if I run into similar issues. I will get back to you as soon as I have some results to share.

Best regards
Torbjørn

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

Manish Kaul — Wed, 13 Jan 2021 09:34:43 GMT

Yes I configure the ADC buffer using 'nrf_drv_saadc_buffer_convert()' and right after that trigger the start task (NRF_SAADC_TASK_START).

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

ovrebekk — Wed, 13 Jan 2021 09:27:44 GMT

I can't see any reason why those channel settings should prevent the continuous sampling from working.

Do you make sure to configure the ADC buffers before you trigger the start task?

Best regards
Torbjørn

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

Manish Kaul — Tue, 12 Jan 2021 09:52:27 GMT

Hey

Yes , the API takes care of that.

I pass 2000 as cc upon calling the function during initialization. The following is the code for initialization function:

bool SDL_Mic_Init(void)
{
  uint32_t ret_code=false;
  
  
  ret_code=nrf_drv_saadc_init(NULL, mic_callback);  //ADC Initialization
  
  if(ret_code==NRFX_SUCCESS)
  { 
    nrf_saadc_channel_config_t adc_channel=NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(MIC_INPUT_DATA_PIN);
    
    ret_code=nrf_drv_saadc_channel_init(MIC_ADC_CHANNEL,&adc_channel);
    if(ret_code==NRFX_SUCCESS)
      ret_code=true;
    
    nrf_saadc_continuous_mode_enable(2000); //for 8K sample rate (16000000/2000=8000Hz)
  }
  
  return ret_code;
}

Could there be anything wrong with the adc channel initialization in the above posted code snippet, which as you can see I have used as default ?

#define NRFX_SAADC_DEFAULT_CHANNEL_CONFIG_SE(PIN_P) \
{                                                   \
    .resistor_p = NRF_SAADC_RESISTOR_DISABLED,      \
    .resistor_n = NRF_SAADC_RESISTOR_DISABLED,      \
    .gain       = NRF_SAADC_GAIN1_6,                \
    .reference  = NRF_SAADC_REFERENCE_INTERNAL,     \
    .acq_time   = NRF_SAADC_ACQTIME_10US,           \
    .mode       = NRF_SAADC_MODE_SINGLE_ENDED,      \
    .burst      = NRF_SAADC_BURST_DISABLED,         \
    .pin_p      = (nrf_saadc_input_t)(PIN_P),       \
    .pin_n      = NRF_SAADC_INPUT_DISABLED          \
}

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

ovrebekk — Tue, 12 Jan 2021 07:30:53 GMT

Did you make sure to set bit 12 in the SAMPLERATE register to enable the local timer?

Best regards
Torbjørn

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

Manish Kaul — Mon, 11 Jan 2021 09:13:01 GMT

Okay I'll try to do that and take a look at the example as well. But I still don't understand one thing, why do I need to use timer when I want to do continuous sampling. Why can't I just set the sample rate in the register as 8KHz (16Mhz/2000) and trigger ADC_START_TASK (NRF_SAADC_TASK_START)

As I understand (and also from the comment documentation) , it should convert samples at the specified sample rate till RAM buffer is full and once the RAM buffer is full I should receive NRFX_SAADC_EVT_DONE event and upon this event I just transmit the buffer.

When I try to do that, it just converts one sample and stops. Can you please explain that ?

RE: Issues in reading analog mic data over SAADC pin of nRF52810.

ovrebekk — Wed, 06 Jan 2021 09:11:14 GMT

The problem is that callback configured through the app_timer will be affected by other interrupts and latencies in the system, and is not suited for scheduling very rapid events.

The app_timer is normally only used for event that happen at a slower rate, and where you can accept some delays in the execution.

For triggering ADC samples it is recommended to use a separate TIMER or RTC module, and have it trigger the ADC in the background using the PPI module. Then you don't have to run any code to trigger ADC sampling, and it will not be affected by other interrupts in the system.

For an example of how to implement this please have a look at the saadc example in the SDK:
\nRF5_SDK_17.0.2_d674dde\examples\peripheral\saadc

Best regards
Torbjørn