ESP32/main/battery_monitor.c

#include "battery_monitor.h"

#include <stdbool.h>

#include "esp_adc/adc_cali.h"
#include "esp_adc/adc_cali_scheme.h"
#include "esp_adc/adc_oneshot.h"
#include "esp_check.h"
#include "esp_err.h"
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "freertos/portmacro.h"
#include "freertos/task.h"

static const char *TAG = "battery";

#define BATTERY_ADC_UNIT ADC_UNIT_1
#define BATTERY_ADC_CHANNEL ADC_CHANNEL_3
#define BATTERY_ADC_ATTEN ADC_ATTEN_DB_12
#define BATTERY_DIVIDER 3
#define BATTERY_EMPTY_MV 2500
#define BATTERY_FULL_MV 4200

static adc_oneshot_unit_handle_t s_adc_handle;
static adc_cali_handle_t s_cali_handle;
static bool s_cali_enabled;
static portMUX_TYPE s_battery_mux = portMUX_INITIALIZER_UNLOCKED;
static int s_latest_percent;
static int s_latest_millivolts;
static bool s_has_latest;

typedef struct {
    int millivolts;
    int raw_avg;
    int pin_millivolts;
    int samples;
} battery_reading_t;

static int clamp_percent(int value)
{
    if (value < 0) {
        return 0;
    }
    if (value > 100) {
        return 100;
    }
    return value;
}

static int battery_percent_from_mv(int mv)
{
    if (mv <= BATTERY_EMPTY_MV) {
        return 0;
    }
    if (mv >= BATTERY_FULL_MV) {
        return 100;
    }

    const int range_mv = BATTERY_FULL_MV - BATTERY_EMPTY_MV;
    return clamp_percent(((mv - BATTERY_EMPTY_MV) * 100 + range_mv / 2) / range_mv);
}

static esp_err_t battery_adc_init(void)
{
    adc_oneshot_unit_init_cfg_t unit_config = {
        .unit_id = BATTERY_ADC_UNIT,
        .clk_src = ADC_RTC_CLK_SRC_DEFAULT,
        .ulp_mode = ADC_ULP_MODE_DISABLE,
    };
    ESP_RETURN_ON_ERROR(adc_oneshot_new_unit(&unit_config, &s_adc_handle), TAG, "adc unit init failed");

    adc_oneshot_chan_cfg_t channel_config = {
        .atten = BATTERY_ADC_ATTEN,
        .bitwidth = ADC_BITWIDTH_DEFAULT,
    };
    ESP_RETURN_ON_ERROR(adc_oneshot_config_channel(s_adc_handle, BATTERY_ADC_CHANNEL, &channel_config),
                        TAG, "adc channel config failed");

#if ADC_CALI_SCHEME_CURVE_FITTING_SUPPORTED
    adc_cali_curve_fitting_config_t cali_config = {
        .unit_id = BATTERY_ADC_UNIT,
        .chan = BATTERY_ADC_CHANNEL,
        .atten = BATTERY_ADC_ATTEN,
        .bitwidth = ADC_BITWIDTH_DEFAULT,
    };
    esp_err_t cali_ret = adc_cali_create_scheme_curve_fitting(&cali_config, &s_cali_handle);
    s_cali_enabled = (cali_ret == ESP_OK);
    if (!s_cali_enabled) {
        ESP_LOGW(TAG, "ADC calibration unavailable: %s", esp_err_to_name(cali_ret));
    }
#endif
    return ESP_OK;
}

static battery_reading_t read_battery(void)
{
    int raw_sum = 0;
    int mv_sum = 0;
    int samples = 0;
    battery_reading_t reading = { 0 };

    for (int i = 0; i < 8; i++) {
        int raw = 0;
        if (adc_oneshot_read(s_adc_handle, BATTERY_ADC_CHANNEL, &raw) != ESP_OK) {
            continue;
        }

        raw_sum += raw;
        samples++;

        if (s_cali_enabled) {
            int pin_mv = 0;
            if (adc_cali_raw_to_voltage(s_cali_handle, raw, &pin_mv) == ESP_OK) {
                mv_sum += pin_mv;
            }
        }
    }

    if (samples == 0) {
        return reading;
    }

    reading.samples = samples;
    reading.raw_avg = raw_sum / samples;

    if (s_cali_enabled && mv_sum > 0) {
        reading.pin_millivolts = mv_sum / samples;
        reading.millivolts = reading.pin_millivolts * BATTERY_DIVIDER;
        return reading;
    }

    reading.pin_millivolts = (reading.raw_avg * 3100) / 4095;
    reading.millivolts = reading.pin_millivolts * BATTERY_DIVIDER;
    return reading;
}

static void battery_task(void *arg)
{
    (void)arg;
    int log_ticks = 0;

    while (1) {
        battery_reading_t reading = read_battery();
        int percent = battery_percent_from_mv(reading.millivolts);
        portENTER_CRITICAL(&s_battery_mux);
        s_latest_percent = percent;
        s_latest_millivolts = reading.millivolts;
        s_has_latest = true;
        portEXIT_CRITICAL(&s_battery_mux);

        if (log_ticks < 6 || (log_ticks % 6) == 0) {
            ESP_LOGI(TAG, "adc raw=%d pin_mv=%d battery_mv=%d percent=%d cali=%d samples=%d",
                     reading.raw_avg, reading.pin_millivolts, reading.millivolts,
                     percent, s_cali_enabled ? 1 : 0, reading.samples);
        }
        log_ticks++;
        vTaskDelay(pdMS_TO_TICKS(10000));
    }
}

void battery_monitor_start(void)
{
    esp_err_t ret = battery_adc_init();
    if (ret != ESP_OK) {
        ESP_LOGW(TAG, "battery monitor disabled: %s", esp_err_to_name(ret));
        portENTER_CRITICAL(&s_battery_mux);
        s_latest_percent = 0;
        s_latest_millivolts = 0;
        s_has_latest = true;
        portEXIT_CRITICAL(&s_battery_mux);
        return;
    }

    xTaskCreate(battery_task, "battery", 4096, NULL, 2, NULL);
}

bool battery_monitor_take_latest(int *percent, int *millivolts)
{
    if (percent == NULL || millivolts == NULL) {
        return false;
    }

    bool has_latest = false;
    portENTER_CRITICAL(&s_battery_mux);
    if (s_has_latest) {
        *percent = s_latest_percent;
        *millivolts = s_latest_millivolts;
        s_has_latest = false;
        has_latest = true;
    }
    portEXIT_CRITICAL(&s_battery_mux);

    return has_latest;
}