InfiniTime/src/components/battery/BatteryController.cpp

#include "BatteryController.h"
#include <hal/nrf_gpio.h>
#include <nrfx_saadc.h>
#include <libraries/log/nrf_log.h>
#include <algorithm>
#include <math.h>

using namespace Pinetime::Controllers;

#define SAMPLES_IN_BUFFER 1
static nrf_saadc_value_t m_buffer_pool[2][SAMPLES_IN_BUFFER];

static float voltage = 0.0f;
static int percentRemaining = -1;

void Battery::Init() {
  nrf_gpio_cfg_input(chargingPin, (nrf_gpio_pin_pull_t)GPIO_PIN_CNF_PULL_Pullup);
  nrf_gpio_cfg_input(powerPresentPin, (nrf_gpio_pin_pull_t)GPIO_PIN_CNF_PULL_Pullup);
}

void Battery::Update() {

  isCharging = !nrf_gpio_pin_read(chargingPin);
  isPowerPresent = !nrf_gpio_pin_read(powerPresentPin);
  
  // Non blocking read
  SaadcInit();
  nrfx_saadc_sample();
  
}

void Battery::SaadcInit() {
  nrfx_saadc_config_t adcConfig = NRFX_SAADC_DEFAULT_CONFIG;
  APP_ERROR_CHECK(nrfx_saadc_init(&adcConfig, SaadcEventHandler));

  nrf_saadc_channel_config_t adcChannelConfig = {
          .resistor_p = NRF_SAADC_RESISTOR_DISABLED,
          .resistor_n = NRF_SAADC_RESISTOR_DISABLED,
          .gain       = NRF_SAADC_GAIN1_5,
          .reference  = NRF_SAADC_REFERENCE_INTERNAL,
          .acq_time   = NRF_SAADC_ACQTIME_3US,
          .mode       = NRF_SAADC_MODE_SINGLE_ENDED,
          .burst      = NRF_SAADC_BURST_ENABLED,
          .pin_p      = batteryVoltageAdcInput,
          .pin_n      = NRF_SAADC_INPUT_DISABLED
  };
  APP_ERROR_CHECK(nrfx_saadc_channel_init(0, &adcChannelConfig));
  APP_ERROR_CHECK(nrfx_saadc_buffer_convert(m_buffer_pool[0],SAMPLES_IN_BUFFER));
  APP_ERROR_CHECK(nrfx_saadc_buffer_convert(m_buffer_pool[1],SAMPLES_IN_BUFFER));

}

void Battery::SaadcEventHandler(nrfx_saadc_evt_t const * p_event) {
  int avg_sample = 0;
  int i = 0;

  const float battery_max = 4.18; //maximum voltage of battery ( max charging voltage is 4.21 )
  const float battery_min = 3.20;  //minimum voltage of battery before shutdown ( depends on the battery )

  if (p_event->type == NRFX_SAADC_EVT_DONE) {
    
    APP_ERROR_CHECK(nrfx_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER));

    for (i = 0; i < SAMPLES_IN_BUFFER; i++) {
      avg_sample += p_event->data.done.p_buffer[i]; // take N samples in a row
    }
    avg_sample /= i; // average all the samples out

    voltage = (static_cast<float>(avg_sample) * 2.04f) / (1024 / 3.0f);
    voltage = roundf(voltage * 100) / 100;

    percentRemaining = static_cast<int>(((voltage - battery_min) / (battery_max - battery_min)) * 100);

    percentRemaining = std::max(percentRemaining, 0);
    percentRemaining = std::min(percentRemaining, 100);

    nrfx_saadc_uninit();

  }
}


int Battery::PercentRemaining() {
  return percentRemaining;
}

float Battery::Voltage() {
  return voltage;
}