Analog to Digital Converter (ADC) Oneshot Mode Driver
Introduction
The Analog to Digital Converter is integrated on the chip and is capable of measuring analog signals from specific analog IO pins.
ESP32 has {SOC_ADC_PERIPH_NUM} ADC unit(s), which can be used in scenario(s) like:
Generate one-shot ADC conversion result
Generate continuous ADC conversion results
This guide introduces ADC oneshot mode conversion.
Functional Overview
The following sections of this document cover the typical steps to install and operate an ADC:
Resource Allocation - covers which parameters should be set up to get an ADC handle and how to recycle the resources when ADC finishes working.
Unit Configuration - covers the parameters that should be set up to configure the ADC unit, so as to get ADC conversion raw result.
Read Conversion Result - covers how to get ADC conversion raw result.
Hardware Limitations - describes the ADC-related hardware limitations.
Power Management - covers power management-related information.
IRAM Safe - describes tips on how to read ADC conversion raw results when the cache is disabled.
Thread Safety - lists which APIs are guaranteed to be thread-safe by the driver.
Kconfig Options - lists the supported Kconfig options that can be used to make a different effect on driver behavior.
Resource Allocation
The ADC oneshot mode driver is implemented based on ESP32 SAR ADC module. Different ESP chips might have different numbers of independent ADCs. From the oneshot mode driver's point of view, an ADC instance is represented by adc_oneshot_unit_handle_t
.
To install an ADC instance, set up the required initial configuration structure adc_oneshot_unit_init_cfg_t
:
adc_oneshot_unit_init_cfg_t::unit_id
selects the ADC. Please refer to the datasheet to know dedicated analog IOs for this ADC.adc_oneshot_unit_init_cfg_t::clk_src
selects the source clock of the ADC. If set to 0, the driver will fall back to using a default clock source, seeadc_oneshot_clk_src_t
to know the details.adc_oneshot_unit_init_cfg_t::ulp_mode
sets if the ADC will be working under ULP mode.
After setting up the initial configurations for the ADC, call adc_oneshot_new_unit()
with the prepared adc_oneshot_unit_init_cfg_t
. This function will return an ADC unit handle if the allocation is successful.
This function may fail due to various errors such as invalid arguments, insufficient memory, etc. Specifically, when the to-be-allocated ADC instance is registered already, this function will return ESP_ERR_NOT_FOUND
error. Number of available ADC(s) is recorded by SOC_ADC_PERIPH_NUM
.
If a previously created ADC instance is no longer required, you should recycle the ADC instance by calling adc_oneshot_del_unit()
, related hardware and software resources will be recycled as well.
Create an ADC Unit Handle Under Normal Oneshot Mode
adc_oneshot_unit_handle_t adc1_handle;
adc_oneshot_unit_init_cfg_t init_config1 = {
.unit_id = ADC_UNIT_1,
.ulp_mode = ADC_ULP_MODE_DISABLE,
};
ESP_ERROR_CHECK(adc_oneshot_new_unit(&init_config1, &adc1_handle));
Recycle the ADC Unit
ESP_ERROR_CHECK(adc_oneshot_del_unit(adc1_handle));
Unit Configuration
After an ADC instance is created, set up the adc_oneshot_chan_cfg_t
to configure ADC IOs to measure analog signal:
adc_oneshot_chan_cfg_t::atten
, ADC attenuation. Refer to Datasheet >ADC Characteristics
.adc_oneshot_chan_cfg_t::bitwidth
, the bitwidth of the raw conversion result.
Note
For the IO corresponding ADC channel number, check datasheet to know the ADC IOs.
Additionally, adc_continuous_io_to_channel()
and adc_continuous_channel_to_io()
can be used to know the ADC channels and ADC IOs.
To make these settings take effect, call adc_oneshot_config_channel()
with the above configuration structure. You should specify an ADC channel to be configured as well. Function adc_oneshot_config_channel()
can be called multiple times to configure different ADC channels. The Driver will save each of these channel configurations internally.
Configure Two ADC Channels
adc_oneshot_chan_cfg_t config = {
.bitwidth = ADC_BITWIDTH_DEFAULT,
.atten = ADC_ATTEN_DB_12,
};
ESP_ERROR_CHECK(adc_oneshot_config_channel(adc1_handle, EXAMPLE_ADC1_CHAN0, &config));
ESP_ERROR_CHECK(adc_oneshot_config_channel(adc1_handle, EXAMPLE_ADC1_CHAN1, &config));
Read Conversion Result
After above configurations, the ADC is ready to measure the analog signal(s) from the configured ADC channel(s). Call adc_oneshot_read()
to get the conversion raw result of an ADC channel.
adc_oneshot_read()
is safe to use. ADC(s) are shared by some other drivers/peripherals, see Hardware Limitations. This function uses mutexes to avoid concurrent hardware usage. Therefore, this function should not be used in an ISR context. This function may fail when the ADC is in use by other drivers/peripherals, and returnESP_ERR_TIMEOUT
. Under this condition, the ADC raw result is invalid.
This function will fail due to invalid arguments.
The ADC conversion results read from this function are raw data. To calculate the voltage based on the ADC raw results, this formula can be used:
Vout = Dout * Vmax / Dmax (1)
where:
Vout |
Digital output result, standing for the voltage. |
---|---|
Dout |
ADC raw digital reading result. |
Vmax |
Maximum measurable input analog voltage, this is related to the ADC attenuation, please refer to TRM > |
Dmax |
Maximum of the output ADC raw digital reading result, which is 2^bitwidth, where bitwidth is the |
To do further calibration to convert the ADC raw result to voltage in mV, please refer to calibration doc Analog to Digital Converter (ADC) Calibration Driver.
Read Raw Result
ESP_ERROR_CHECK(adc_oneshot_read(adc1_handle, EXAMPLE_ADC1_CHAN0, &adc_raw[0][0]));
ESP_LOGI(TAG, "ADC%d Channel[%d] Raw Data: %d", ADC_UNIT_1 + 1, EXAMPLE_ADC1_CHAN0, adc_raw[0][0]);
ESP_ERROR_CHECK(adc_oneshot_read(adc1_handle, EXAMPLE_ADC1_CHAN1, &adc_raw[0][1]));
ESP_LOGI(TAG, "ADC%d Channel[%d] Raw Data: %d", ADC_UNIT_1 + 1, EXAMPLE_ADC1_CHAN1, adc_raw[0][1]);
Hardware Limitations
Random Number Generator (RNG) uses ADC as an input source. When ADC
adc_oneshot_read()
works, the random number generated from RNG will be less random.A specific ADC unit can only work under one operating mode at any one time, either continuous mode or oneshot mode.
adc_oneshot_read()
has provided the protection.ADC2 is also used by Wi-Fi.
adc_oneshot_read()
has provided protection between the Wi-Fi driver and ADC oneshot mode driver.ESP32-DevKitC: GPIO0 cannot be used in oneshot mode, because the DevKit has used it for auto-flash.
ESP-WROVER-KIT: GPIO 0, 2, 4, and 15 cannot be used due to external connections for different purposes.
Power Management
When power management is enabled, i.e., CONFIG_PM_ENABLE is on, the system clock frequency may be adjusted when the system is in an idle state. However, the ADC oneshot mode driver works in a polling routine, the adc_oneshot_read()
will poll the CPU until the function returns. During this period of time, the task in which ADC oneshot mode driver resides will not be blocked. Therefore the clock frequency is stable when reading.
IRAM Safe
By default, all the ADC oneshot mode driver APIs are not supposed to be run when the Cache is disabled. Cache may be disabled due to many reasons, such as Flash writing/erasing, OTA, etc. If these APIs execute when the Cache is disabled, you will probably see errors like Illegal Instruction
or Load/Store Prohibited
.
Thread Safety
Above functions are guaranteed to be thread-safe. Therefore, you can call them from different RTOS tasks without protection by extra locks.
adc_oneshot_del_unit()
is not thread-safe. Besides, concurrently calling this function may result in failures of the above thread-safe APIs.
Kconfig Options
CONFIG_ADC_ONESHOT_CTRL_FUNC_IN_IRAM controls where to place the ADC fast read function (IRAM or Flash), see IRAM Safe for more details.
Application Examples
peripherals/adc/oneshot_read demonstrates how to obtain a one-shot ADC reading from a GPIO pin using the ADC one-shot mode driver and how to use the ADC Calibration functions to obtain a calibrated result in mV on ESP32.
API Reference
Header File
This header file can be included with:
#include "hal/adc_types.h"
Structures
-
struct adc_digi_pattern_config_t
ADC digital controller pattern configuration.
-
struct adc_digi_output_data_t
ADC digital controller (DMA mode) output data format. Used to analyze the acquired ADC (DMA) data.
Note
ESP32: Only
type1
is valid. ADC2 does not support DMA mode.Note
ESP32-S2: Member
channel
can be used to judge the validity of the ADC data, because the role of the arbiter may get invalid ADC data.Public Members
-
uint16_t data
ADC real output data info. Resolution: 12 bit.
ADC real output data info. Resolution: 11 bit.
-
uint16_t channel
ADC channel index info.
ADC channel index info. For ESP32-S2: If (channel < ADC_CHANNEL_MAX), The data is valid. If (channel > ADC_CHANNEL_MAX), The data is invalid.
-
struct adc_digi_output_data_t::[anonymous]::[anonymous] type1
ADC type1
-
uint16_t unit
ADC unit index info. 0: ADC1; 1: ADC2.
-
struct adc_digi_output_data_t::[anonymous]::[anonymous] type2
When the configured output format is 11bit.
-
uint16_t val
Raw data value
-
uint16_t data
Type Definitions
-
typedef soc_periph_adc_digi_clk_src_t adc_oneshot_clk_src_t
Clock source type of oneshot mode which uses digital controller.
-
typedef soc_periph_adc_digi_clk_src_t adc_continuous_clk_src_t
Clock source type of continuous mode which uses digital controller.
Enumerations
-
enum adc_unit_t
ADC unit.
Values:
-
enumerator ADC_UNIT_1
SAR ADC 1.
-
enumerator ADC_UNIT_2
SAR ADC 2.
-
enumerator ADC_UNIT_1
-
enum adc_channel_t
ADC channels.
Values:
-
enumerator ADC_CHANNEL_0
ADC channel.
-
enumerator ADC_CHANNEL_1
ADC channel.
-
enumerator ADC_CHANNEL_2
ADC channel.
-
enumerator ADC_CHANNEL_3
ADC channel.
-
enumerator ADC_CHANNEL_4
ADC channel.
-
enumerator ADC_CHANNEL_5
ADC channel.
-
enumerator ADC_CHANNEL_6
ADC channel.
-
enumerator ADC_CHANNEL_7
ADC channel.
-
enumerator ADC_CHANNEL_8
ADC channel.
-
enumerator ADC_CHANNEL_9
ADC channel.
-
enumerator ADC_CHANNEL_0
-
enum adc_atten_t
ADC attenuation parameter. Different parameters determine the range of the ADC.
Values:
-
enumerator ADC_ATTEN_DB_0
No input attenuation, ADC can measure up to approx.
-
enumerator ADC_ATTEN_DB_2_5
The input voltage of ADC will be attenuated extending the range of measurement by about 2.5 dB.
-
enumerator ADC_ATTEN_DB_6
The input voltage of ADC will be attenuated extending the range of measurement by about 6 dB.
-
enumerator ADC_ATTEN_DB_12
The input voltage of ADC will be attenuated extending the range of measurement by about 12 dB.
-
enumerator ADC_ATTEN_DB_11
This is deprecated, it behaves the same as
ADC_ATTEN_DB_12
-
enumerator ADC_ATTEN_DB_0
-
enum adc_bitwidth_t
Values:
-
enumerator ADC_BITWIDTH_DEFAULT
Default ADC output bits, max supported width will be selected.
-
enumerator ADC_BITWIDTH_9
ADC output width is 9Bit.
-
enumerator ADC_BITWIDTH_10
ADC output width is 10Bit.
-
enumerator ADC_BITWIDTH_11
ADC output width is 11Bit.
-
enumerator ADC_BITWIDTH_12
ADC output width is 12Bit.
-
enumerator ADC_BITWIDTH_13
ADC output width is 13Bit.
-
enumerator ADC_BITWIDTH_DEFAULT
-
enum adc_ulp_mode_t
Values:
-
enumerator ADC_ULP_MODE_DISABLE
ADC ULP mode is disabled.
-
enumerator ADC_ULP_MODE_FSM
ADC is controlled by ULP FSM.
-
enumerator ADC_ULP_MODE_RISCV
ADC is controlled by ULP RISCV.
-
enumerator ADC_ULP_MODE_DISABLE
-
enum adc_digi_convert_mode_t
ADC digital controller (DMA mode) work mode.
Values:
-
enumerator ADC_CONV_SINGLE_UNIT_1
Only use ADC1 for conversion.
-
enumerator ADC_CONV_SINGLE_UNIT_2
Only use ADC2 for conversion.
-
enumerator ADC_CONV_BOTH_UNIT
Use Both ADC1 and ADC2 for conversion simultaneously.
-
enumerator ADC_CONV_ALTER_UNIT
Use both ADC1 and ADC2 for conversion by turn. e.g. ADC1 -> ADC2 -> ADC1 -> ADC2 .....
-
enumerator ADC_CONV_SINGLE_UNIT_1
-
enum adc_digi_output_format_t
ADC digital controller (DMA mode) output data format option.
Values:
-
enumerator ADC_DIGI_OUTPUT_FORMAT_TYPE1
-
enumerator ADC_DIGI_OUTPUT_FORMAT_TYPE2
-
enumerator ADC_DIGI_OUTPUT_FORMAT_TYPE1
-
enum adc_digi_iir_filter_t
ADC IIR Filter ID.
Values:
-
enumerator ADC_DIGI_IIR_FILTER_0
Filter 0.
-
enumerator ADC_DIGI_IIR_FILTER_1
Filter 1.
-
enumerator ADC_DIGI_IIR_FILTER_0
-
enum adc_digi_iir_filter_coeff_t
IIR Filter Coefficient.
Values:
-
enumerator ADC_DIGI_IIR_FILTER_COEFF_2
The filter coefficient is 2.
-
enumerator ADC_DIGI_IIR_FILTER_COEFF_4
The filter coefficient is 4.
-
enumerator ADC_DIGI_IIR_FILTER_COEFF_8
The filter coefficient is 8.
-
enumerator ADC_DIGI_IIR_FILTER_COEFF_16
The filter coefficient is 16.
-
enumerator ADC_DIGI_IIR_FILTER_COEFF_64
The filter coefficient is 64.
-
enumerator ADC_DIGI_IIR_FILTER_COEFF_2
Header File
This header file can be included with:
#include "esp_adc/adc_oneshot.h"
This header file is a part of the API provided by the
esp_adc
component. To declare that your component depends onesp_adc
, add the following to your CMakeLists.txt:REQUIRES esp_adc
or
PRIV_REQUIRES esp_adc
Functions
-
esp_err_t adc_oneshot_new_unit(const adc_oneshot_unit_init_cfg_t *init_config, adc_oneshot_unit_handle_t *ret_unit)
Create a handle to a specific ADC unit.
Note
This API is thread-safe. For more details, see ADC programming guide
- Parameters
init_config -- [in] Driver initial configurations
ret_unit -- [out] ADC unit handle
- Returns
ESP_OK: On success
ESP_ERR_INVALID_ARG: Invalid arguments
ESP_ERR_NO_MEM: No memory
ESP_ERR_NOT_FOUND: The ADC peripheral to be claimed is already in use
ESP_FAIL: Clock source isn't initialised correctly
-
esp_err_t adc_oneshot_config_channel(adc_oneshot_unit_handle_t handle, adc_channel_t channel, const adc_oneshot_chan_cfg_t *config)
Set ADC oneshot mode required configurations.
Note
This API is thread-safe. For more details, see ADC programming guide
- Parameters
handle -- [in] ADC handle
channel -- [in] ADC channel to be configured
config -- [in] ADC configurations
- Returns
ESP_OK: On success
ESP_ERR_INVALID_ARG: Invalid arguments
-
esp_err_t adc_oneshot_read(adc_oneshot_unit_handle_t handle, adc_channel_t chan, int *out_raw)
Get one ADC conversion raw result.
Note
This API is thread-safe. For more details, see ADC programming guide
Note
This API should NOT be called in an ISR context
- Parameters
handle -- [in] ADC handle
chan -- [in] ADC channel
out_raw -- [out] ADC conversion raw result
- Returns
ESP_OK: On success
ESP_ERR_INVALID_ARG: Invalid arguments
ESP_ERR_TIMEOUT: Timeout, the ADC result is invalid
-
esp_err_t adc_oneshot_del_unit(adc_oneshot_unit_handle_t handle)
Delete the ADC unit handle.
Note
This API is thread-safe. For more details, see ADC programming guide
- Parameters
handle -- [in] ADC handle
- Returns
ESP_OK: On success
ESP_ERR_INVALID_ARG: Invalid arguments
ESP_ERR_NOT_FOUND: The ADC peripheral to be disclaimed isn't in use
-
esp_err_t adc_oneshot_io_to_channel(int io_num, adc_unit_t *const unit_id, adc_channel_t *const channel)
Get ADC channel from the given GPIO number.
- Parameters
io_num -- [in] GPIO number
unit_id -- [out] ADC unit
channel -- [out] ADC channel
- Returns
ESP_OK: On success
ESP_ERR_INVALID_ARG: Invalid argument
ESP_ERR_NOT_FOUND: The IO is not a valid ADC pad
-
esp_err_t adc_oneshot_channel_to_io(adc_unit_t unit_id, adc_channel_t channel, int *const io_num)
Get GPIO number from the given ADC channel.
- Parameters
unit_id -- [in] ADC unit
channel -- [in] ADC channel
io_num -- [out] GPIO number
- -- ESP_OK: On success
ESP_ERR_INVALID_ARG: Invalid argument
-
esp_err_t adc_oneshot_get_calibrated_result(adc_oneshot_unit_handle_t handle, adc_cali_handle_t cali_handle, adc_channel_t chan, int *cali_result)
Convenience function to get ADC calibrated result.
This is an all-in-one function which does:
oneshot read ADC raw result
calibrate the raw result and convert it into calibrated result (in mV)
- Parameters
handle -- [in] ADC oneshot handle, you should call adc_oneshot_new_unit() to get this handle
cali_handle -- [in] ADC calibration handle, you should call adc_cali_create_scheme_x() in adc_cali_scheme.h to create a handle
chan -- [in] ADC channel
cali_result -- [out] Calibrated ADC result (in mV)
- Returns
ESP_OK Other return errors from adc_oneshot_read() and adc_cali_raw_to_voltage()
Structures
-
struct adc_oneshot_unit_init_cfg_t
ADC oneshot driver initial configurations.
Public Members
-
adc_unit_t unit_id
ADC unit.
-
adc_oneshot_clk_src_t clk_src
Clock source.
-
adc_ulp_mode_t ulp_mode
ADC controlled by ULP, see
adc_ulp_mode_t
-
adc_unit_t unit_id
-
struct adc_oneshot_chan_cfg_t
ADC channel configurations.
Public Members
-
adc_atten_t atten
ADC attenuation.
-
adc_bitwidth_t bitwidth
ADC conversion result bits.
-
adc_atten_t atten
Type Definitions
-
typedef struct adc_oneshot_unit_ctx_t *adc_oneshot_unit_handle_t
Type of ADC unit handle for oneshot mode.