esp-idf/components/esp_adc_cal/esp_adc_cal_esp32s3.c

/*
 * SPDX-FileCopyrightText: 2020-2021 Espressif Systems (Shanghai) CO LTD
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include "esp_types.h"
#include "esp_err.h"
#include "esp_log.h"
#include "esp_check.h"
#include "driver/adc.h"
#include "hal/adc_types.h"
#include "esp_efuse_rtc_calib.h"
#include "esp_adc_cal.h"

const static char LOG_TAG[] = "ADC_CALI";

/* ------------------------ Characterization Constants ---------------------- */

//coeff_a is actually a float number
//it is scaled to put them into uint32_t so that the headers do not have to be changed
static const int coeff_a_scaling = 1000000;

/**
 * @note Error Calculation
 * Coefficients for calculating the reading voltage error.
 * Four sets of coefficients for atten0 ~ atten3 respectively.
 *
 * For each item, first element is the Coefficient, second element is the Multiple. (Coefficient / Multiple) is the real coefficient.
 *
 * @note {0,0} stands for unused item
 * @note In case of the overflow, these coeffcients are recorded as Absolute Value
 * @note For atten0 ~ 2, error = a1 * X^2 + a2 * X + a3; For atten3, error = a1 * X^4 + a2 * X^3 + a3 * X^2 + a4 * X + a5;
 */
const static uint64_t adc_error_coef_atten[4][10][2] = {
                                                            {{9798249589, 1e15}, {50871540569528, 1e16}, {3, 1}, {0, 0}, {0, 0},     //ADC1 atten0
                                                             {36615265189, 1e16}, {1353548869615, 1e16}, {3, 1}, {0, 0}, {0, 0}},    //ADC2 atten0

                                                            {{101379430548, 1e16}, {49393185868806, 1e16}, {3, 1}, {0, 0}, {0, 0},   //ADC1 atten1
                                                             {118964995959, 1e16}, {66319894226185, 1e16}, {2, 1}, {0, 0}, {0, 0}},  //ADC2 atten1

                                                            {{208385525314, 1e16}, {147640181047414, 1e16}, {2, 1}, {0, 0}, {0, 0},  //ADC1 atten2
                                                             {259011467956, 1e16}, {200996773954387, 1e16}, {1, 1}, {0, 0}, {0, 0}}, //ADC2 atten2

                                                            {{13515, 1e15}, {70769718, 1e15}, {1297891447611, 1e16}, {644334888647536, 1e16}, {1,1},    //ADC1 atten3
                                                             {15038, 1e15}, {79672528, 1e15}, {1478791187119, 1e16}, {755717904943462, 1e16}, {1,1}}    //ADC2 atten3
                                                        };
const static int32_t adc_error_sign[4][10] = {
                                                {1, -1, -1, 0, 0,   //ADC1 atten0
                                                 1,  1, -1, 0, 0},  //ADC2 atten0

                                                {1, -1, -1, 0, 0,   //ADC1 atten1
                                                 1, -1, -1, 0, 0},  //ADC2 atten1

                                                {1, -1, -1, 0, 0,   //ADC1 atten2
                                                 1, -1, -1, 0, 0},  //ADC2 atten2

                                                {1, -1, 1, -1, -1,  //ADC1 atten3
                                                 1, -1, 1, -1,  1}  //ADC2 atten3
                                            };

/* -------------------- Characterization Helper Data Types ------------------ */
typedef struct {
    uint32_t voltage;
    uint32_t digi;
} adc_calib_data_ver1_t;

typedef struct {
    char version_num;
    adc_unit_t adc_num;
    adc_atten_t atten_level;
    union {
        adc_calib_data_ver1_t ver1;
    } ref_data;
} adc_calib_info_t;


//To get the reference point (Dout, Vin)
static esp_err_t get_reference_point(int version_num, adc_unit_t adc_num, adc_atten_t atten, adc_calib_info_t *calib_info)
{
    assert(version_num == 1);
    esp_err_t ret;

    calib_info->version_num = version_num;
    calib_info->adc_num = adc_num;
    calib_info->atten_level = atten;

    uint32_t voltage = 0;
    uint32_t digi = 0;
    ret = esp_efuse_rtc_calib_get_cal_voltage(version_num, ((adc_num == ADC_UNIT_1) ? 0 : 1), atten, &digi, &voltage);
    assert(ret == ESP_OK);
    calib_info->ref_data.ver1.voltage = voltage;
    calib_info->ref_data.ver1.digi = digi;
    return ret;
}

esp_err_t esp_adc_cal_check_efuse(esp_adc_cal_value_t source)
{
    if (source != ESP_ADC_CAL_VAL_EFUSE_TP_FIT) {
        return ESP_ERR_NOT_SUPPORTED;
    }
    uint8_t adc_encoding_version = esp_efuse_rtc_calib_get_ver();
    if (adc_encoding_version != 1) {
        // current version only accepts encoding ver 1.
        return ESP_ERR_INVALID_VERSION;
    }
    return ESP_OK;
}

/*
 * Get an expected linear relationship btwn Vin and Dout
 */
static void calculate_characterization_coefficients(const adc_calib_info_t *parsed_data, esp_adc_cal_characteristics_t *chars)
{
    chars->coeff_a = coeff_a_scaling * parsed_data->ref_data.ver1.voltage / parsed_data->ref_data.ver1.digi;
    chars->coeff_b = 0;
    ESP_LOGV(LOG_TAG, "Calib V1, Cal Voltage = %d, Digi out = %d, Coef_a = %d\n", parsed_data->ref_data.ver1.voltage, parsed_data->ref_data.ver1.digi, chars->coeff_a);
}

esp_adc_cal_value_t esp_adc_cal_characterize(adc_unit_t adc_num,
        adc_atten_t atten,
        adc_bits_width_t bit_width,
        uint32_t default_vref,
        esp_adc_cal_characteristics_t *chars)
{
    (void) default_vref;

    // Check parameters
    ESP_RETURN_ON_FALSE(adc_num == ADC_UNIT_1 || adc_num == ADC_UNIT_2, ESP_ADC_CAL_VAL_NOT_SUPPORTED, LOG_TAG, "Invalid unit num");
    ESP_RETURN_ON_FALSE(chars != NULL, ESP_ADC_CAL_VAL_NOT_SUPPORTED, LOG_TAG, "Ivalid characteristic");
    ESP_RETURN_ON_FALSE(atten < ADC_ATTEN_MAX, ESP_ADC_CAL_VAL_NOT_SUPPORTED, LOG_TAG, "Invalid attenuation");

    int version_num = esp_efuse_rtc_calib_get_ver();
    ESP_RETURN_ON_FALSE(version_num == 1, ESP_ADC_CAL_VAL_NOT_SUPPORTED, LOG_TAG, "No calibration efuse burnt");

    memset(chars, 0, sizeof(esp_adc_cal_characteristics_t));

    adc_calib_info_t calib_info = {0};
    // make sure adc is calibrated.
    get_reference_point(version_num, adc_num, atten, &calib_info);
    calculate_characterization_coefficients(&calib_info, chars);

    // Initialize remaining fields
    chars->adc_num = adc_num;
    chars->atten = atten;
    chars->bit_width = bit_width;

    return ESP_ADC_CAL_VAL_EFUSE_TP_FIT;
}

static int32_t get_reading_error(uint64_t v_cali_1, uint8_t adc_num, uint8_t atten)
{
    if (v_cali_1 == 0) {
        return 0;
    }

    uint8_t term_max = (atten == 3) ? 5 : 3;
    int32_t error = 0;
    uint64_t coeff = 0;
    uint64_t term[5] = {0};

    /**
     * For atten0 ~ 2:
     * error = a1 * X^2 + a2 * X + a3;
     *
     * For atten3:
     * error = a1 * X^4 + a2 * X^3 + a3 * X^2 + a4 * X + a5;
     */

    //Calculate all the power beforehand
    term[term_max-1] = 1;
    term[term_max-2] = v_cali_1;
    for (int term_id = term_max - 3; term_id >= 0; term_id--) {
        term[term_id] = term[term_id + 1] * v_cali_1;
    }

    //Calculate each term
    uint8_t coef_id_start = (adc_num == ADC_UNIT_1) ? 0 : 5;
    for (int i = 0; i < term_max; i++) {
        coeff = adc_error_coef_atten[atten][coef_id_start + i][0];
        term[i] = term[i] * coeff;
        ESP_LOGV(LOG_TAG, "big coef is %llu, big term%d is %llu, coef_id is %d", coeff, i, term[i], coef_id_start + i);

        term[i] = term[i] / adc_error_coef_atten[atten][coef_id_start + i][1];
        error += (int32_t)term[i] * adc_error_sign[atten][i];
        ESP_LOGV(LOG_TAG, "term%d is %llu, error is %d", i, term[i], error);
    }

    return error;
}

uint32_t esp_adc_cal_raw_to_voltage(uint32_t adc_reading, const esp_adc_cal_characteristics_t *chars)
{
    assert(chars != NULL);

    //ADC reading won't exceed 4096. Otherwise the raw reading result is wrong, the next calculation will overflow.
    assert(adc_reading < 4096);

    uint32_t voltage = 0;
    int32_t error = 0;
    uint64_t v_cali_1 = 0;

    //raw * gradient * 1000000
    v_cali_1 = adc_reading * chars->coeff_a;
    //convert to real number
    v_cali_1 = v_cali_1 / coeff_a_scaling;
    ESP_LOGV(LOG_TAG, "v_cali_1 is %llu", v_cali_1);

    error = get_reading_error(v_cali_1, chars->adc_num, chars->atten);
    voltage = (int32_t)v_cali_1 - error;

    return voltage;
}