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esp_adc_cal.h
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esp_adc_cal.h
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/*
* SPDX-FileCopyrightText: 2015-2022 Espressif Systems (Shanghai) CO LTD
*
* SPDX-License-Identifier: Apache-2.0
*/
#ifndef __ESP_ADC_CAL_H__
#define __ESP_ADC_CAL_H__
#include <stdint.h>
#include "esp_err.h"
#include "driver/adc.h"
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief Type of calibration value used in characterization
*/
typedef enum {
ESP_ADC_CAL_VAL_EFUSE_VREF = 0, /**< Characterization based on reference voltage stored in eFuse*/
ESP_ADC_CAL_VAL_EFUSE_TP = 1, /**< Characterization based on Two Point values stored in eFuse*/
ESP_ADC_CAL_VAL_DEFAULT_VREF = 2, /**< Characterization based on default reference voltage*/
ESP_ADC_CAL_VAL_EFUSE_TP_FIT = 3, /**< Characterization based on Two Point values and fitting curve coefficients stored in eFuse */
ESP_ADC_CAL_VAL_MAX,
ESP_ADC_CAL_VAL_NOT_SUPPORTED = ESP_ADC_CAL_VAL_MAX,
} esp_adc_cal_value_t;
/**
* @brief Structure storing characteristics of an ADC
*
* @note Call esp_adc_cal_characterize() to initialize the structure
*/
typedef struct {
adc_unit_t adc_num; /**< ADC number*/
adc_atten_t atten; /**< ADC attenuation*/
adc_bits_width_t bit_width; /**< ADC bit width */
uint32_t coeff_a; /**< Gradient of ADC-Voltage curve*/
uint32_t coeff_b; /**< Offset of ADC-Voltage curve*/
uint32_t vref; /**< Vref used by lookup table*/
const uint32_t *low_curve; /**< Pointer to low Vref curve of lookup table (NULL if unused)*/
const uint32_t *high_curve; /**< Pointer to high Vref curve of lookup table (NULL if unused)*/
uint8_t version; /**< ADC Calibration */
} esp_adc_cal_characteristics_t;
/**
* @brief Checks if ADC calibration values are burned into eFuse
*
* This function checks if ADC reference voltage or Two Point values have been
* burned to the eFuse of the current ESP32
*
* @param value_type Type of calibration value (ESP_ADC_CAL_VAL_EFUSE_VREF or ESP_ADC_CAL_VAL_EFUSE_TP)
* @note in ESP32S2, only ESP_ADC_CAL_VAL_EFUSE_TP is supported. Some old ESP32S2s do not support this, either.
* In which case you have to calibrate it manually, possibly by performing your own two-point calibration on the chip.
*
* @return
* - ESP_OK: The calibration mode is supported in eFuse
* - ESP_ERR_NOT_SUPPORTED: Error, eFuse values are not burned
* - ESP_ERR_INVALID_ARG: Error, invalid argument (ESP_ADC_CAL_VAL_DEFAULT_VREF)
*/
esp_err_t esp_adc_cal_check_efuse(esp_adc_cal_value_t value_type);
/**
* @brief Characterize an ADC at a particular attenuation
*
* This function will characterize the ADC at a particular attenuation and generate
* the ADC-Voltage curve in the form of [y = coeff_a * x + coeff_b].
* Characterization can be based on Two Point values, eFuse Vref, or default Vref
* and the calibration values will be prioritized in that order.
*
* @note
* For ESP32, Two Point values and eFuse Vref calibration can be enabled/disabled using menuconfig.
* For ESP32s2, only Two Point values calibration and only ADC_WIDTH_BIT_13 is supported. The parameter default_vref is unused.
*
*
* @param[in] adc_num ADC to characterize (ADC_UNIT_1 or ADC_UNIT_2)
* @param[in] atten Attenuation to characterize
* @param[in] bit_width Bit width configuration of ADC
* @param[in] default_vref Default ADC reference voltage in mV (Only in ESP32, used if eFuse values is not available)
* @param[out] chars Pointer to empty structure used to store ADC characteristics
*
* @return
* - ESP_ADC_CAL_VAL_EFUSE_VREF: eFuse Vref used for characterization
* - ESP_ADC_CAL_VAL_EFUSE_TP: Two Point value used for characterization (only in Linear Mode)
* - ESP_ADC_CAL_VAL_DEFAULT_VREF: Default Vref used for characterization
*/
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);
/**
* @brief Convert an ADC reading to voltage in mV
*
* This function converts an ADC reading to a voltage in mV based on the ADC's
* characteristics.
*
* @note Characteristics structure must be initialized before this function
* is called (call esp_adc_cal_characterize())
*
* @param[in] adc_reading ADC reading
* @param[in] chars Pointer to initialized structure containing ADC characteristics
*
* @return Voltage in mV
*/
uint32_t esp_adc_cal_raw_to_voltage(uint32_t adc_reading, const esp_adc_cal_characteristics_t *chars);
/**
* @brief Reads an ADC and converts the reading to a voltage in mV
*
* This function reads an ADC then converts the raw reading to a voltage in mV
* based on the characteristics provided. The ADC that is read is also
* determined by the characteristics.
*
* @note The Characteristics structure must be initialized before this
* function is called (call esp_adc_cal_characterize())
*
* @param[in] channel ADC Channel to read
* @param[in] chars Pointer to initialized ADC characteristics structure
* @param[out] voltage Pointer to store converted voltage
*
* @return
* - ESP_OK: ADC read and converted to mV
* - ESP_ERR_INVALID_ARG: Error due to invalid arguments
* - ESP_ERR_INVALID_STATE: Reading result is invalid. Try to read again.
*/
esp_err_t esp_adc_cal_get_voltage(adc_channel_t channel, const esp_adc_cal_characteristics_t *chars, uint32_t *voltage);
#ifdef __cplusplus
}
#endif
#endif /* __ESP_ADC_CAL_H__ */