Using ADC in FreeRTOS

Owned by Natalia Sofronova
Last updated: May 22, 2024
6 min read

This application note explains how to use the STM32H7 ADC in the FreeRTOS demo application.

1. Understanding ADC Interfaces

1.1. FreeRTOS ADC Implementation

The FreeRTOS BSP makes use of the STM32CubeH7 software component to provide a device driver for the STM32H7 ADC. The driver is configured (enabled / disabled) at the BSP build time, using the HAL_ADC_MODULE_ENABLED configuration option, defined in the stm32h7xx_hal_conf.h file.

1.2. FreeRTOS ADC C-Binding API

The ADC driver implements the following C-binding API:

Function

Description

Comments

HAL_StatusTypeDef HAL_ADC_Init(ADC_HandleTypeDef * hadc)

 

Initialize the ADC peripheral and regular group according to the specified parameters by hadc

hadc is a pointer to a structure that contains the configuration information for ADC (ADC handle); returns one of {HAL_OK, HAL_ERROR, HAL_BUSY, HAL_TIMEOUT}

HAL_StatusTypeDef HAL_ADC_DeInit(ADC_HandleTypeDef * hadc)

 

Deinitialize the ADC peripheral registers to their default reset values

hadc is an ADC handle; returns one of {HAL_OK, HAL_ERROR, HAL_BUSY, HAL_TIMEOUT}

HAL_StatusTypeDef HAL_ADC_ConfigChannel(ADC_HandleTypeDef * hadc, ADC_ChannelConfTypeDef * sConfig)

 

Configure a channel to be assigned to ADC group regular

hadc is an ADC handle; sConfig is a ADC configuration structure; returns one of {HAL_OK, HAL_ERROR, HAL_BUSY, HAL_TIMEOUT}

HAL_StatusTypeDef HAL_ADCEx_Calibration_Start((ADC_HandleTypeDef * hadc, uint32_t CalibrationMode, uint32_t SingleDiff)

 

Perform an ADC automatic self-calibration

hadc is an ADC handle

HAL_StatusTypeDef HAL_ADC_Start(ADC_HandleTypeDef * hadc)

 

Enable ADC, starts conversion of regular group

hadc is an ADC handle; returns one of {HAL_OK, HAL_ERROR, HAL_BUSY, HAL_TIMEOUT}

HAL_StatusTypeDef HAL_ADC_PollForConversion(ADC_HandleTypeDef * hadc, uint32_t Timeout)

 

Wait for regular group conversion to be completed

hadc is an ADC handle; returns one of {HAL_OK, HAL_ERROR, HAL_BUSY, HAL_TIMEOUT}

uint32_t HAL_ADC_GetValue(ADC_HandleTypeDef * hadc)

 

Get ADC regular group conversion result

hadc is an ADC handle; returns a ADC group regular conversion data

The ADC_HandleTypeDef data structure used in this API has the following definition:

typedef struct { ADC_TypeDef *Instance; /* Register base address */ ADC_InitTypeDef Init; /* ADC initialization parameters and regular conversions setting */ DMA_HandleTypeDef *DMA_Handle; /* Pointer DMA Handler */ HAL_LockTypeDef Lock; /* ADC locking object */ __IO uint32_t State; /* ADC communication state (bit-map of ADC states) */ __IO uint32_t ErrorCode; /* ADC Error code */ ADC_InjectionConfigTypeDef InjectionConfig ; /* ADC injected channel configuration build-up structure */ } ADC_HandleTypeDef;

The ADC_InjectionConfigTypeDef data structure used in ADC_HandleTypeDef has the following definition:

typedef struct { uint32_t ContextQueue; /* Injected channel configuration context */ uint32_t ChannelCount; /* Number of channels in the injected sequence */ } ADC_InjectionConfigTypeDef;

The ADC_ChannelConfTypeDef data structure used in HAL_ADC_ConfigChannel interface has the following definition:

typedef struct { uint32_t Channel; /* Specify the channel to configure into ADC regular group. */ uint32_t Rank; /* Specify the rank in the regular group sequencer. */ uint32_t SamplingTime; /* Sampling time value to be set for the selected channel. */ uint32_t SingleDiff; /* Select single-ended or differential input. */ uint32_t OffsetNumber; /* Select the offset number. */ uint32_t Offset; /* Define the offset to be subtracted from the raw converted data. */ FunctionalState OffsetRightShift; /* Define the Right-shift data after Offset correction. */ FunctionalState OffsetSignedSaturation; /* Specify whether the Signed saturation feature is used or not.*/ } ADC_ChannelConfTypeDef;

2. ADC CLI Command

The FreeRTOS application implements the following ADC related CLI command:

Command

Description

Comments

adc_se<nadc> <chnl>

Run the ADC test in the single-ended input mode

nadc is the ADC number, chnl is the channel number

3. Validating ADC Operation

Use the following step-wise procedure to validate the FreeRTOS ADC operation:

  1. Connect a 2.6V voltage to the ADC pin.

    • On the STM32H7-BSB Rev 1A board: P4.7 (PA4) pin.

    • On the STM32H7-BSB Rev 2A board: P4.4 (PA4) pin.

  2. Power cycle the target board and let it boot to the FreeRTOS CLI.

  3. From the CLI, run the adc_se command:

  4. Compare the output result with the input voltage. Make sure the two match.

  5. Change the input voltage to 0.6V.

  6. Run the adc_se command again:

  7. Compare the output result with the input voltage. Make sure the two match.