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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "esp_system.h"
#include "esp_err.h"
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/gpio.h"
#include "driver/adc.h"
#include "esp_adc_cal.h"

typedef long i32;
static esp_adc_cal_characteristics_t *adc_chars;
static const adc1_channel_t channel = ADC1_CHANNEL_6;
static const adc_bits_width_t width = ADC_WIDTH_BIT_12;
static const adc_atten_t atten = ADC_ATTEN_DB_11;
static uint8 adc_configured = 0;

void adc_init() {
    /* gpio config */
    esp_err_t err;
    gpio_config_t io_conf = {};
    io_conf.intr_type = GPIO_INTR_DISABLE;
    io_conf.mode = GPIO_MODE_INPUT;
    io_conf.pin_bit_mask =  1ULL << GPIO_NUM_7;
    io_conf.pull_down_en = 0;
    io_conf.pull_up_en = 0;
    err = gpio_config(&io_conf);
    
    /* config attenuation */
    adc1_config_channel_atten(channel, atten);

    /* config bit width */
    adc1_config_width(width);
    adc_chars = calloc(1, sizeof(esp_adc_cal_characteristics_t));
    esp_adc_cal_value_t val_type = esp_adc_cal_characterize(ADC_UNIT_1, 
        atten,
        width,
        1100,
        adc_chars);
}

i32 adc_read() {
    #define BATADC_SAMPLE_SZ 32
    // multisampling
    for (u8 i = 0; i < BATADC_SAMPLE_SZ; i++) {
        i32 raw = adc1_get_raw((adc1_channel_t)channel);
        adc_reading += raw;
        sys_delay_us(20);
    }

    adc_reading /= (BATADC_SAMPLE_SZ);
    voltage = esp_adc_cal_raw_to_voltage(adc_reading, adc_chars) * 2u;
    return voltage;
}

void app_main(void)
{
	adc_init();
	for (;;) {
		ESP_LOGI(TAG, "VBat: %ld", adc_read());
		vTaskDelay(1000);
	}
}