About SAADC, Easy-DMA and channels (nRF5_SDK)

[Jarmo]

There's an example saadc_pca10036 in the SDK. I am wondering how this piece of code works in that example:

void saadc_init(void)
{
    ret_code_t err_code;
    nrf_saadc_channel_config_t channel_config =
            NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);
    err_code = nrf_drv_saadc_init(NULL, saadc_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0],SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
    
    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1],SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
}

Specifically, why there are two calls of same function, nrf_drv_saadc_buffer_convert()? Does it set some kind of double-buffering?

In my case, I have four ADC-inputs I want to sample 200 times per second each. How should I configure the SAADC subsystem?

EDIT: Also, how do I know which channel was triggered when I get into the callback (below)?

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
   if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
   ...

[Jarmo]

It is still unclear for me how to set-up several channels. For example, if I need two channels, the code is maybe something like this:

#define CHANNELS       2
#define BUFFERSIZE   128
int16_t Buffers[CHANNELS][2][BUFFERSIZE];

void init_adc(void)
{
    nrf_drv_saadc_init(NULL, saadc_callback);

    // set up first channel
    nrf_saadc_channel_config_t channel_config =
         NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);
    nrf_drv_saadc_channel_init(0, &channel_config);
    // set-up double buffering for the first channel
    nrf_drv_saadc_buffer_convert(Buffers[0][0], BUFFERSIZE);
    nrf_drv_saadc_buffer_convert(Buffers[0][1], BUFFERSIZE);

    // set up second channel
    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN1);
    nrf_drv_saadc_channel_init(1, &channel_config);
    // set-up double buffering for the second channel
    nrf_drv_saadc_buffer_convert(Buffers[1][0], BUFFERSIZE);
    nrf_drv_saadc_buffer_convert(Buffers[1][1], BUFFERSIZE);
}

And the event handler:

static
  void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
  {
      if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
      {
          nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, BUFFERSIZE);
          // TODO: How do I know which of the two channels was triggered?
      }
  }

As said in the TODO-line, how do I know which of the two channels was triggered? Do I need to compare the pointer p_event->data.done.p_buffer against the pointers I set earlier with the call to *_buffer_convert() at my init_adc()?

[Jarmo]

Thanks for comment. How do I enable scan mode?