Set up ADC nrf52832 on a continuous transformation but it does not work.

[Alex_Golubev]

Hey.
Here is the code:

     

volatile int16_t result = 0;

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_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_40us        << SAADC_CH_CONFIG_TACQ_Pos);
     
    NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_AnalogInput0 << SAADC_CH_PSELP_PSELP_Pos;
    NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;
    
    NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_14bit << SAADC_RESOLUTION_VAL_Pos;
    
    
    NRF_SAADC->RESULT.MAXCNT = 1;
    NRF_SAADC->RESULT.PTR = (uint32_t)&result;
    
      // No automatic sampling, will trigger with TASKS_SAMPLE.
    NRF_SAADC->SAMPLERATE = 0x400 | SAADC_SAMPLERATE_MODE_Timers << SAADC_SAMPLERATE_MODE_Pos;
    
    NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Enabled << SAADC_ENABLE_ENABLE_Pos;
    
    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));
    
    // Start the SAADC and wait for the started event.
    NRF_SAADC->TASKS_START = 1;
    while (NRF_SAADC->EVENTS_STARTED == 0);
    NRF_SAADC->EVENTS_STARTED = 0;

    // 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;

The result variable does not change depending on the input voltage AIN0.

[Einar Thorsrud]

Hi,

The only problem I see is that you only have room for one sample in your result buffer, so it is not surprising that you do not get different samples. Try using a large buffer, and update NRF_SAADC->RESULT.MAXCNT accordingly.

[Alex_Golubev]

Thanks for the answer.

increased buffer size NRF_SAADC->RESULT.MAXCNT = 64; 

volatile int16_t result[64];
volatile float precise_result = 0;   

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_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_40us        << SAADC_CH_CONFIG_TACQ_Pos);
     
    NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_AnalogInput0 << SAADC_CH_PSELP_PSELP_Pos;
    NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;
    
    NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_14bit << SAADC_RESOLUTION_VAL_Pos;
    
    NRF_SAADC->RESULT.MAXCNT = 64;
    NRF_SAADC->RESULT.PTR = (uint32_t)&result;
    
      // No automatic sampling, will trigger with TASKS_SAMPLE.
    NRF_SAADC->SAMPLERATE = 0x80 | SAADC_SAMPLERATE_MODE_Timers << SAADC_SAMPLERATE_MODE_Pos;
    
    NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Enabled << SAADC_ENABLE_ENABLE_Pos;
    
    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));
    
    NRF_SAADC->TASKS_START = 1;
    while (NRF_SAADC->EVENTS_STARTED == 0);
    NRF_SAADC->EVENTS_STARTED = 0;

    NRF_SAADC->TASKS_SAMPLE = 1;
    while (NRF_SAADC->EVENTS_END == 0);
    NRF_SAADC->EVENTS_END = 0;

The entire buffer  is full 16380. 

How to make cyclic data transfer ADC -> DMA -> RAM? 

[Einar Thorsrud]

There is no way to configure a cyclic data transfer in HW like this. The SAADC peripheral will fill up RAM via DMA, but you will get an event when the buffer is filled and have to provide a new buffer and start the process again to continue sampling. (This means that you will have some problems getting an accurate time between the last sample of one series and the first sample of the next series).

[Alex_Golubev]

thanks.