SAADC and retriggering

[Jannebozz]

Hi,

I´m using the NRF52810 device and have an issue with the SAADC peripheral.

I basically have 2 channel where i want to do some averaging to improve noise.

The setup is as follows:

// Configure SAADC singled-ended channel, Internal reference (0.6V) and 1/2 gain. This gives input range 0-1.2V
  NRF_SAADC->CH[0].CONFIG = (SAADC_CH_CONFIG_GAIN_Gain1_2    << SAADC_CH_CONFIG_GAIN_Pos) |
                            (SAADC_CH_CONFIG_MODE_SE         << SAADC_CH_CONFIG_MODE_Pos) |
                            (SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos) |
                            (SAADC_CH_CONFIG_RESN_Bypass     << SAADC_CH_CONFIG_RESN_Pos) |
                            (SAADC_CH_CONFIG_RESP_Bypass     << SAADC_CH_CONFIG_RESP_Pos) |
                            (SAADC_CH_CONFIG_TACQ_3us        << SAADC_CH_CONFIG_TACQ_Pos) |
                            (SAADC_CH_CONFIG_BURST_Enabled   << SAADC_CH_CONFIG_BURST_Pos);
  // Configure the SAADC channel with VDD as positive input, no negative input(single ended).
  NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_AnalogInput2 << SAADC_CH_PSELP_PSELP_Pos;
  NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;
  
 
  //Channel 6 - NTC
    // Configure SAADC singled-ended channel, Reference (VDD/4) and 1/4 gain. This gives input range 0-VDD
  NRF_SAADC->CH[1].CONFIG = (SAADC_CH_CONFIG_GAIN_Gain1_4    << SAADC_CH_CONFIG_GAIN_Pos) |
                            (SAADC_CH_CONFIG_MODE_SE         << SAADC_CH_CONFIG_MODE_Pos) |
                            (SAADC_CH_CONFIG_REFSEL_VDD1_4   << SAADC_CH_CONFIG_REFSEL_Pos) |
                            (SAADC_CH_CONFIG_RESN_Bypass     << SAADC_CH_CONFIG_RESN_Pos) |
                            (SAADC_CH_CONFIG_RESP_Bypass     << SAADC_CH_CONFIG_RESP_Pos) |
                            (SAADC_CH_CONFIG_TACQ_3us        << SAADC_CH_CONFIG_TACQ_Pos) |
                            (SAADC_CH_CONFIG_BURST_Enabled   << SAADC_CH_CONFIG_BURST_Pos);

  // Configure the SAADC channel with VDD as positive input, no negative input(single ended).
  NRF_SAADC->CH[1].PSELP = SAADC_CH_PSELP_PSELP_AnalogInput6 << SAADC_CH_PSELP_PSELP_Pos;
  NRF_SAADC->CH[1].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;
  
  // Configure the SAADC resolution.
  NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_14bit << SAADC_RESOLUTION_VAL_Pos;

  // Configure result to be put in RAM at the location of "result" variable.
  // Average result will be sent to memory, 2 channels means 2 average values.
  //NRF_SAADC->RESULT.MAXCNT = 2;
  //NRF_SAADC->OVERSAMPLE = SAADC_OVERSAMPLE_OVERSAMPLE_Over16x << SAADC_OVERSAMPLE_OVERSAMPLE_Pos;
  NRF_SAADC->RESULT.MAXCNT = 2;
  NRF_SAADC->OVERSAMPLE = SAADC_OVERSAMPLE_OVERSAMPLE_Over256x    << SAADC_OVERSAMPLE_OVERSAMPLE_Pos;
  //adcResult is of size 2
  NRF_SAADC->RESULT.PTR = (uint32_t)&adcResult[0];

  // No automatic sampling, will trigger with TASKS_SAMPLE.
  NRF_SAADC->SAMPLERATE = SAADC_SAMPLERATE_MODE_Task << SAADC_SAMPLERATE_MODE_Pos;

  // Enable SAADC (would capture analog pins if they were used in CH[0].PSELP)
  NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Enabled << SAADC_ENABLE_ENABLE_Pos;

  // Calibrate the SAADC (only needs to be done once in a while)
  NRF_SAADC->TASKS_CALIBRATEOFFSET = 1;
  while (NRF_SAADC->EVENTS_CALIBRATEDONE == 0);
  NRF_SAADC->EVENTS_CALIBRATEDONE = 0;
  while (NRF_SAADC->STATUS == (SAADC_STATUS_STATUS_Busy <<SAADC_STATUS_STATUS_Pos));

When the adc is started (task started), i want to collect several samples in a loop.

void StartAdcWaitForResult()
{
  // Do a SAADC sample, will put the result in the configured RAM buffer.
  NRF_SAADC->TASKS_SAMPLE = 1;
  while (NRF_SAADC->EVENTS_END == 0);
  NRF_SAADC->EVENTS_END = 0;
}

while(sampleCounter-- > 0)
        {
            StartAdcWaitForResult();
            raw_signals[0] = adcResult[0];
            raw_signals[1] = adcResult[0];
            
            SendData();
        }

It works the first time, then the StartAdcWaitForResult hangs (since the end event never happens again).
If i trigger the TASK_STOP and then TASK_START before StartAdcWaitForResult it works, not sure why.

But I assume this is not how it´s suppose to be working...?

[Jørgen Holmefjord]

Hi,

Do the code work without oversampling, or without offset calibration? Where/how do you trigger the START task? Have you tested with higher acquisition time? We have had quite a few erratas with tacq < 5 us in nRF52832, but most of these should have been fixed in nRF52810.

Which revision is the nRF52810 chip you are testing this on? 

Best regards,
Jørgen

[Jørgen Holmefjord]

You can check the markings on the chip against the table I linked, or post the marking here.

I do not have any nRF52810 chips available to test with at the moment, but if you can provide an example project that can reproduce the issue, I will try to have someone take a look at it.

[Jannebozz]

The marking says
52810
QCAAC0
1740AB

[Jørgen Holmefjord]

Ok, that is a revision 1 chip. I will try to get hold of a similar chip and test if I can reproduce the issue.

[Jørgen Holmefjord]

I looked over your code again. I see that you have the MAXCNT register set to the number of enabled channels. When you have started the SAADC, and the buffer has been filled, the END event will be generated. At this point, the SAADC will be in stopped state. If you want to sample again, you need to trigger the START task again. If you want to sample multiple times in a loop, without triggering START, you can increase the buffer size and wait for the DONE/RESULTDONE events between each sample.

[Jannebozz]

Hi,
Ok, that makes sense. Will try and see. Thanks!