Simpler ADC read function doesn't port to the right channel?

[MikeLemon]

Hello there,

I'm trying to learn how to use some of the perepherials of the nrf52832 with the DK,

trying to learn a little about the SAADC I found some example modified it a little to work but in there it takes 8 lines of code to preform a single Analog read now looking a little at the API reference of info center I found this funstion called: nrf_drv_saadc_sample_convert();

which says there that it preforms a single ADC read but when trying it the values don't seem to change corresponding to the probed voltage on the pin here is my code:

#include <nrf.h>

int main(void)
{

   volatile unsigned int VDD = 0;
  volatile unsigned int X = 0;
  volatile unsigned int Y = 0;
  volatile float precise_result = 0;

  // Start HFCLK from crystal oscillator, this will give the SAADC higher accuracy
 // NRF_CLOCK->TASKS_HFCLKSTART = 1;
  //while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
  //NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;

  // Configure SAADC singled-ended channel, Internal reference (0.6V) and 1/6 gain.
  NRF_SAADC->CH[0].CONFIG = (SAADC_CH_CONFIG_GAIN_Gain1_6     << 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);

  // Configure the SAADC channel with VDD as positive input, no negative input(single ended).
 
  NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;

  // Configure the SAADC resolution.
  NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_10bit << SAADC_RESOLUTION_VAL_Pos;

  // Configure result to be put in RAM at the location of "result" variable.
  NRF_SAADC->RESULT.MAXCNT = 1;
 

  // 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));

  


  while (1)
  {

  /*

  NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_AnalogInput1 << SAADC_CH_PSELP_PSELP_Pos;
  NRF_SAADC->RESULT.PTR = (int)&X;
  // 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;

  NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_AnalogInput2 << SAADC_CH_PSELP_PSELP_Pos;
  NRF_SAADC->RESULT.PTR = (int)&Y;
  // 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;


  // Stop the SAADC, since it's not used anymore.
// NRF_SAADC->TASKS_STOP = 1;
//  while (NRF_SAADC->EVENTS_STOPPED == 0);
//  NRF_SAADC->EVENTS_STOPPED = 0;
    //__WFE();
*/
    
  
  
   // nrf_drv_saadc_sample_convert(SAADC_CH_PSELN_PSELN_VDD, &VDD);
    nrf_drv_saadc_sample_convert(1, &X);
    nrf_drv_saadc_sample_convert(2, &Y);

    

  }
}

in the main function the code in the comment seem to work maybe I'm doing something wrong.

[Jørgen Holmefjord]

Hi,

You cannot use the SAADC driver functions without initializing the SAADC driver first. You need to do the peripheral and channel configuration as described in the SAADC driver documentation. Setting the registers directly will not work with the driver.

If you check the error codes returned from your call to nrf_drv_saadc_sample_convert, it will most likely tell you that the driver is not initialized/busy.

Best regards,

Jørgen

[MikeLemon]

Ok great thought is was being done here

NRF_SAADC->CH[0].CONFIG = (SAADC_CH_CONFIG_GAIN_Gain1_6     << 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);

Now reading a little about it I understood that you have to init the function with nrf_drv_saadc_init(NULL, ); but don't understand what is that event handler still(saw that quite alot around the examples) and what can you enter there as an example?

[Jørgen Holmefjord]

The event handler is used to run the SAADC driver in non-blocking mode. You setup a buffer, start the sampling, and get an interrupt that is triggering the event handler, when the sample buffer is filled. This will allow the CPU to do other tasks, or go to sleep while sampling is performed. In blocking mode, the CPU is busy-looping while waiting for the sampling to complete, occupating the CPU.

[MikeLemon]

Makes sense but do you have an example for what can you enter in that p_event? maybe for blocking and non blocking mode.

[Jørgen Holmefjord]

Please have a look at the SAADC peripheral example in the SDK. It show the use of non-blocking operation and how to use the event handler. There is also two examples available in this GitHub repository.

[MikeLemon]

To me it looks that both of them use the timers to perform an SAADC sample I mean one is more complicated than the other one just calibrates one uses bluetooth for some reason all none sens.