Simple one shot ADC example

RE: Simple one shot ADC example

Edvin — Mon, 16 Mar 2020 07:23:22 GMT

Philip, you seem to miss my point.

You can remove saadc_sampling_event_init() and saadc_sampling_event_enable() from my main.c file, but you will have to call nrf_drv_saadc_sample() from somewhere.

If I removed this from the file before sending it to you, I would be sending a project that does nothing.

Try to remove those functions, and add nrf_drv_saadc_sample() to whatever event you want to trigger the sampling from.

RE: Simple one shot ADC example

ephimee — Sat, 14 Mar 2020 08:24:49 GMT

If I follow your code.

In the function main() there's a call to saadc_sampling_event_init().

In the function saadc_sampling_event_init() there's a call to nrf_drv_timer_init().

I tried to remove all timer related stuff, but then it no longer works. I'm looking specifically for an example without timers. Which means without any reference to *timer* function calls and without any *timer* includes.

RE: Simple one shot ADC example

Edvin — Thu, 12 Mar 2020 09:48:13 GMT

This is what I tried to show with the attached example.

Use

nrf_drv_saadc_sample();

NRF_SAADC->TASKS_SAMPLE = 1;

to trigger one sample from anywhere in your project. The point was that I detached the PPI from the timer, and called it in the interrupt. You can of course call it from anywhere.

RE: Simple one shot ADC example

ephimee — Thu, 12 Mar 2020 08:23:49 GMT

Hi Edwin,

Thanks for your reply.

This code does not use one shot mode but continues mode.

Also this code uses timers. I don't have timers available because they are being used by other peripherals.

I know the advantage of not waiting for the CPU. But because of the limited resources I rather have a simple example that waits to the CPU than a complex example that uses a lot of fancy includes & functionality that make no sense to me.

Is it even possible to do ADC without timer? All I need is:

int value = analogRead(NRF_SAADC_INPUT_AIN7);

I don't mind to wait 50ms.

/Philip

RE: Simple one shot ADC example

hmolesworth — Wed, 11 Mar 2020 16:05:39 GMT

The code looks broadly correct assuming that pin P0.26 provides the excitation voltage for something connected on pin P0.31. (edited, I misread the original)

You are missing an errata workaround, however, detailed here:

  // 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))
     ;
  // [Errata 86] SAADC: Triggering START task after offset calibration may write a sample to RAM
  //  This anomaly applies to IC Rev. Rev 2, build codes QFAA-Ex0, CIAA-Ex0, QFAB-Ex0.
  //  Calibration should follow the pattern STOP -> STOPPED -> CALIBRATEOFFSET -> CALIBRATEDONE -> STOP -> STOPPED -> START
  // Stop the SAADC and wait for the stopped event as per Errata 86
  NRF_SAADC->TASKS_STOP = 1;
  while (NRF_SAADC->EVENTS_STOPPED == 0)
     ;
  NRF_SAADC->EVENTS_STOPPED = 0;

Additionally I would suggest looking at the binary result in case there is some issue with IDE floating point settings in (say) printf as below:

  printf("result: 0x%04X, precise_result: %0.2f\n", result, precise_result);
  printf("result: 0x%04X, precise_result: %4.2f\n", result, precise_result);

%0.2f does not do what you expect; try 5.2% maybe :-)

RE: Simple one shot ADC example

Edvin — Wed, 11 Mar 2020 15:52:17 GMT

Hello,

I agree that this example is a bit complex for showing some simple functionality.

But it is actually quite simple to change this from using PPI to trigger it manually. Please check out the attached main.c file, which is a modification from the saadc examples main.c file:

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 *    such product, must reproduce the above copyright notice, this list of
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 *    materials provided with the distribution.
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 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
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 *    Nordic Semiconductor ASA integrated circuit.
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/** @file
 * @defgroup nrf_adc_example main.c
 * @{
 * @ingroup nrf_adc_example
 * @brief ADC Example Application main file.
 *
 * This file contains the source code for a sample application using ADC.
 *
 * @image html example_board_setup_a.jpg "Use board setup A for this example."
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "nrf.h"
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "boards.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "app_util_platform.h"
#include "nrf_pwr_mgmt.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define SAMPLES_IN_BUFFER 5
volatile uint8_t state = 1;

static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(0);
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];
static nrf_ppi_channel_t     m_ppi_channel;
static uint32_t              m_adc_evt_counter;


void timer_handler(nrf_timer_event_t event_type, void * p_context)
{
    NRF_LOG_INFO("Timer interrupt");
    
    NRF_SAADC->TASKS_SAMPLE = 1;
    /*
    // Alternatively, you can use the driver to trigger a sample:
    nrf_drv_saadc_sample();
    */
}


void saadc_sampling_event_init(void)
{
    ret_code_t err_code;

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
    err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);
    APP_ERROR_CHECK(err_code);

    /* setup m_timer for compare event every 400ms */
    uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_timer, 400);

    nrf_drv_timer_extended_compare(&m_timer,
                                   NRF_TIMER_CC_CHANNEL0,
                                   ticks,
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   true);
    nrf_drv_timer_enable(&m_timer);

    uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,
                                                                                NRF_TIMER_CC_CHANNEL0);
    uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();

    /* setup ppi channel so that timer compare event is triggering sample task in SAADC */
//    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
//    APP_ERROR_CHECK(err_code);

//    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
//                                          timer_compare_event_addr,
//                                          saadc_sample_task_addr);
    APP_ERROR_CHECK(err_code);
}


void saadc_sampling_event_enable(void)
{
    ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);

    APP_ERROR_CHECK(err_code);
}


void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        ret_code_t err_code;

        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);

        int i;
        NRF_LOG_INFO("ADC event number: %d", (int)m_adc_evt_counter);

        for (i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            NRF_LOG_INFO("%d", p_event->data.done.p_buffer[i]);
        }
        m_adc_evt_counter++;
    }
}


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);

}


/**
 * @brief Function for main application entry.
 */
int main(void)
{
    uint32_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();

    ret_code_t ret_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(ret_code);

    saadc_init();
    saadc_sampling_event_init();
    //saadc_sampling_event_enable();
    NRF_LOG_INFO("SAADC HAL simple example started.");

    while (1)
    {
        nrf_pwr_mgmt_run();
        NRF_LOG_FLUSH();
    }
}


/** @} */

Please note that I changed one parameter in nrf_drv_timer_extended_compare() as well, in order to trigger the timer interrupt handler in the application.

The advantage of using PPI is that you don't need to rely on/wait for the CPU in order to trigger the sampling, but it is not necessary to use it.

Best regards,

Edvin