ADC

Overview

API Reference

group adc_interface

ADC driver APIs.

Defines

ADC_ACQ_TIME_MICROSECONDS

Acquisition time is expressed in microseconds.

ADC_ACQ_TIME_NANOSECONDS

Acquisition time is expressed in nanoseconds.

ADC_ACQ_TIME_TICKS

Acquisition time is expressed in ADC ticks.

ADC_ACQ_TIME(unit, value)

Macro for composing the acquisition time value in given units.

ADC_ACQ_TIME_DEFAULT

Value indicating that the default acquisition time should be used.

ADC_ACQ_TIME_UNIT(time)
ADC_ACQ_TIME_VALUE(time)

Typedefs

typedef enum adc_action (*adc_sequence_callback)(const struct device *dev, const struct adc_sequence *sequence, uint16_t sampling_index)

Type definition of the optional callback function to be called after a requested sampling is done.

Return

Action to be performed by the driver. See adc_action.

Parameters

  • dev: Pointer to the device structure for the driver instance.

  • sequence: Pointer to the sequence structure that triggered the sampling. This parameter points to a copy of the structure that was supplied to the call that started the sampling sequence, thus it cannot be used with the CONTAINER_OF() macro to retrieve some other data associated with the sequence. Instead, the adc_sequence_options::user_data field should be used for such purpose.

  • sampling_index: Index (0-65535) of the sampling done.

typedef int (*adc_api_channel_setup)(const struct device *dev, const struct adc_channel_cfg *channel_cfg)

Type definition of ADC API function for configuring a channel. See adc_channel_setup() for argument descriptions.

typedef int (*adc_api_read)(const struct device *dev, const struct adc_sequence *sequence)

Type definition of ADC API function for setting a read request. See adc_read() for argument descriptions.

typedef int (*adc_api_read_async)(const struct device *dev, const struct adc_sequence *sequence, struct k_poll_signal *async)

Type definition of ADC API function for setting an asynchronous read request. See adc_read_async() for argument descriptions.

Enums

enum adc_gain

ADC channel gain factors.

Values:

enumerator ADC_GAIN_1_6

x 1/6.

enumerator ADC_GAIN_1_5

x 1/5.

enumerator ADC_GAIN_1_4

x 1/4.

enumerator ADC_GAIN_1_3

x 1/3.

enumerator ADC_GAIN_1_2

x 1/2.

enumerator ADC_GAIN_2_3

x 2/3.

enumerator ADC_GAIN_1

x 1.

enumerator ADC_GAIN_2

x 2.

enumerator ADC_GAIN_3

x 3.

enumerator ADC_GAIN_4

x 4.

enumerator ADC_GAIN_8

x 8.

enumerator ADC_GAIN_16

x 16.

enumerator ADC_GAIN_32

x 32.

enumerator ADC_GAIN_64

x 64.

enumerator ADC_GAIN_128

x 128.

enum adc_reference

ADC references.

Values:

enumerator ADC_REF_VDD_1

VDD.

enumerator ADC_REF_VDD_1_2

VDD/2.

enumerator ADC_REF_VDD_1_3

VDD/3.

enumerator ADC_REF_VDD_1_4

VDD/4.

enumerator ADC_REF_INTERNAL

Internal.

enumerator ADC_REF_EXTERNAL0

External, input 0.

enumerator ADC_REF_EXTERNAL1

External, input 1.

enum adc_action

Action to be performed after a sampling is done.

Values:

enumerator ADC_ACTION_CONTINUE

The sequence should be continued normally.

enumerator ADC_ACTION_REPEAT

The sampling should be repeated. New samples or sample should be read from the ADC and written in the same place as the recent ones.

enumerator ADC_ACTION_FINISH

The sequence should be finished immediately.

Functions

int adc_gain_invert(enum adc_gain gain, int32_t *value)

Invert the application of gain to a measurement value.

For example, if the gain passed in is ADC_GAIN_1_6 and the referenced value is 10, the value after the function returns is 60.

Parameters

  • gain: the gain used to amplify the input signal.

  • value: a pointer to a value that initially has the effect of the applied gain but has that effect removed when this function successfully returns. If the gain cannot be reversed the value remains unchanged.

Return Value

  • 0: if the gain was successfully reversed

  • -EINVAL: if the gain could not be interpreted

static inline int adc_raw_to_millivolts(int32_t ref_mv, enum adc_gain gain, uint8_t resolution, int32_t *valp)

Convert a raw ADC value to millivolts.

This function performs the necessary conversion to transform a raw ADC measurement to a voltage in millivolts.

Parameters

  • ref_mv: the reference voltage used for the measurement, in millivolts. This may be from adc_ref_internal() or a known external reference.

  • gain: the ADC gain configuration used to sample the input

  • resolution: the number of bits in the absolute value of the sample. For differential sampling this may be one less than the resolution in struct adc_sequence.

  • valp: pointer to the raw measurement value on input, and the corresponding millivolt value on successful conversion. If conversion fails the stored value is left unchanged.

Return Value

  • 0: on successful conversion

  • -EINVAL: if the gain is not reversible

int adc_channel_setup(const struct device *dev, const struct adc_channel_cfg *channel_cfg)

Configure an ADC channel.

It is required to call this function and configure each channel before it is selected for a read request.

Parameters

  • dev: Pointer to the device structure for the driver instance.

  • channel_cfg: Channel configuration.

Return Value

  • 0: On success.

  • -EINVAL: If a parameter with an invalid value has been provided.

int adc_read(const struct device *dev, const struct adc_sequence *sequence)

Set a read request.

If invoked from user mode, any sequence struct options for callback must be NULL.

Parameters

  • dev: Pointer to the device structure for the driver instance.

  • sequence: Structure specifying requested sequence of samplings.

Return Value

  • 0: On success.

  • -EINVAL: If a parameter with an invalid value has been provided.

  • -ENOMEM: If the provided buffer is to small to hold the results of all requested samplings.

  • -ENOTSUP: If the requested mode of operation is not supported.

  • -EBUSY: If another sampling was triggered while the previous one was still in progress. This may occur only when samplings are done with intervals, and it indicates that the selected interval was too small. All requested samples are written in the buffer, but at least some of them were taken with an extra delay compared to what was scheduled.

int adc_read_async(const struct device *dev, const struct adc_sequence *sequence, struct k_poll_signal *async)

Set an asynchronous read request.

If invoked from user mode, any sequence struct options for callback must be NULL.

Note

This function is available only if CONFIG_ADC_ASYNC is selected.

Return

0 on success, negative error code otherwise. See adc_read() for a list of possible error codes.

Parameters

  • dev: Pointer to the device structure for the driver instance.

  • sequence: Structure specifying requested sequence of samplings.

  • async: Pointer to a valid and ready to be signaled struct k_poll_signal. (Note: if NULL this function will not notify the end of the transaction, and whether it went successfully or not).

static inline uint16_t adc_ref_internal(const struct device *dev)

Get the internal reference voltage.

Returns the voltage corresponding to ADC_REF_INTERNAL, measured in millivolts.

Return

a positive value is the reference voltage value. Returns zero if reference voltage information is not available.

struct adc_channel_cfg
#include <adc.h>

Structure for specifying the configuration of an ADC channel.

struct adc_sequence_options
#include <adc.h>

Structure defining additional options for an ADC sampling sequence.

struct adc_sequence
#include <adc.h>

Structure defining an ADC sampling sequence.

struct adc_driver_api
#include <adc.h>

ADC driver API.

This is the mandatory API any ADC driver needs to expose.