main.c

/**
 * Copyright (c) 2014 - 2020, Nordic Semiconductor ASA
 *
 * All rights reserved.
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 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
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/*
   Author : Abdelali Boussetta @rmptxf
   Description : This saadc example uses one channel (AIN1 (P0.3)), samples at 100ms (10 samples) =  get result each (1 second).
   It uses 14Bit as a resolution.
*/

#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 10

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;

// RESULT = [V(P) – V(N) ] * GAIN/REFERENCE * 2(RESOLUTION - m)
// (m=0) if CONFIG.MODE=SE, or (m=1) if CONFIG.MODE=Diff.

// V(N) = 0;
// GAIN = 1/6;
// REFERENCE Voltage = internal (0.6V);
// RESOLUTION : 12 bit;
// m = 0;

// 12bit
// V(P) = RESULT x REFERENCE / ( GAIN x RESOLUTION) = RESULT x (600 / (1/6 x 2^(12)) =  ADC_RESULT x 0.87890625;
//#define ADC_RESULT_IN_MILLI_VOLTS(ADC_RESULT) ((ADC_RESULT * 0.87890625))

// 14bit
// V(P) = RESULT x REFERENCE / ( GAIN x RESOLUTION) = RESULT x (600 / (1/6 x 2^(14)) =  ADC_RESULT x 0.2197265625;
#define ADC_RESULT_IN_MILLI_VOLTS(ADC_RESULT) ((ADC_RESULT * 0.2197265625))


void timer_handler(nrf_timer_event_t event_type, void * p_context)
{

}


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 100ms */
    uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_timer, 100);
    nrf_drv_timer_extended_compare(&m_timer,
                                   NRF_TIMER_CC_CHANNEL0,
                                   ticks,
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
    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)
{
    ret_code_t err_code;

    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {     
        uint32_t buffer_samples = 0;
        uint16_t adc_result = 0;
        uint16_t adc_voltage_mv = 0;

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

        m_adc_evt_counter++;

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

        for (uint8_t i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            buffer_samples += p_event->data.done.p_buffer[i];
        }

        adc_result = buffer_samples/SAMPLES_IN_BUFFER;
        adc_voltage_mv = ADC_RESULT_IN_MILLI_VOLTS(adc_result);

        NRF_LOG_INFO("adc result : %d.", adc_result);
        NRF_LOG_INFO("voltage : %d mV.", adc_voltage_mv);
         
        NRF_LOG_INFO("---------------------------");
    }
}


void saadc_init(void)
{
    ret_code_t err_code;
    // Using the channel default single ended (SE) config
    // pin NRF_SAADC_INPUT_AIN1 : P0.03
    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN1);

    // changing the saadc resolution to 12bit
    nrf_drv_saadc_config_t saadc_config ;
    saadc_config.resolution = NRF_SAADC_RESOLUTION_14BIT;

    err_code = nrf_drv_saadc_init(&saadc_config, 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();
    }
}


/** @} */