This is the Third article in the series of how to use ADC in STM32 and this time we will be using DMA (Direct Memory Access). To view the other two methods, visit ADC using interrupt in STM32 and ADC in STM32 using HAL
Description
DMA or Direct Memory Access is a method that allows and input/output device to send or receive data directly to or from the main memory, bypassing the CPU to speedup memory operations.
The advantage of using DMA is that we can use multi channel conversion. The result of the conversion will be stored in the memory and at any instance during the code, we can access that memory and read ADC values within interrupt service routine.
In this Tutorial I will use two channels, One of them is Internal Temperature Sensor of the Cortex M4 and second is the IR sensor. I will be using STM32CubeMx, Keil IDE and HAL libraries as usual.
NOTE:- Temperature sensor is being used just to show different values for the two channels. I will make a separate tutorial on how to read the Internal Temperature sensor.
So let’s get started
CubeMX Setup
open the cubeMx and select two channels from ADC
Select Channel 0 and Internal temperature
Go to ADC setting and make sure that the setting is as below
Resolution is 12 bit, Scan conversion- enabled, Continuous conversion – enabled number of conversions – 2
Now we have to add a DMA request. Go to DMA Setting Tab and follow the setting in the image below
Enable the ADC1 global interrupt in the NVIC setting tab
Generate the project and open it.
Some Insight into the code:-
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uint32_t adc_buf[2], adc_val[2]; |
As i am using two channels therefore adc_buf should store two bytes and so does adc_val.
Write a callback function to read the values from the buffer whenever the conversion is complete. This is same as writing a callback in interrupt method
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void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc) { for (int i =0; i<2;i++) { adc_val[i] = adc_buf[i]; // store the values in adc_val from buffer } } |
Now whenever the conversion is complete, the values present in adc_buf will be saved in adc_val, which we can read at any instant in our program.
NOTE here that We set DMA in circular mode which means that the conversion will continue in circular mode, latest value overwriting the oldest one.
NOTE here that We set DMA in circular mode which means that the conversion will continue in circular mode, latest value overwriting the oldest one.
Inside main function we need to start ADC with DMA by writing
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HAL_ADC_Start_DMA (&hadc1, (uint32_t *) adc_buf, 2); Here HAL_ADC_Start_DMA takes following arguments ADC_HandleTypeDef* hadc ---> ADC handler uint32_t* pData ---> The destination Buffer address uint32_t Length ---> The length of data to be transferred from ADC peripheral to memory. |
To demonstrate the working here, I am going to write an infinite loop to read the values from buffer every 1 second. I am going to create another variable for debugging purpose, whose value will update every 1 sec.
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uint32_t display_value[2]; main () { ....... .......... while (1) { display_value[0] = adc_val[0]; display_value[1] = adc_val[1]; HAL_Delay (1000); } } |
Result
Compile the code and start debugging.
Add display_val[0] (for channel 0) and display_val[1] (for internal temperature) to the watch list and run the debugger.
Initially the channel 0, which is connected to IR sensor, shows 4095 because there is no obstacle in front of it and internal temperature sensor shows 953. We still have to convert this value to Celsius scale. We will see that part in another tutorial.
display_val[0] = 4095, display_val[1] = 953
display_val[0] = 472, display_val[1] = 953
We can use DMA to do as much conversion as we want (obviously limited by the number of channels present in the microcontroller).
Video
CODE
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#include "main.h" #include "stm32f4xx_hal.h" /* USER CODE BEGIN Includes */ /* USER CODE END Includes */ /* Private variables ---------------------------------------------------------*/ ADC_HandleTypeDef hadc1; DMA_HandleTypeDef hdma_adc1; /* USER CODE BEGIN PV */ /* Private variables ---------------------------------------------------------*/ /* USER CODE END PV */ /* Private function prototypes -----------------------------------------------*/ void SystemClock_Config(void); void Error_Handler(void); static void MX_GPIO_Init(void); static void MX_DMA_Init(void); static void MX_ADC1_Init(void); /* USER CODE BEGIN PFP */ /* Private function prototypes -----------------------------------------------*/ uint32_t adc_buf[2], adc_val[2], display_value[2]; /* USER CODE END PFP */ /* USER CODE BEGIN 0 */ void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc) { for (int i=0;i<2;i++) { adc_val[i] = adc_buf[i]; } } /* USER CODE END 0 */ int main(void) { /* USER CODE BEGIN 1 */ /* USER CODE END 1 */ /* MCU Configuration----------------------------------------------------------*/ /* Reset of all peripherals, Initializes the Flash interface and the Systick. */ HAL_Init(); /* Configure the system clock */ SystemClock_Config(); /* Initialize all configured peripherals */ MX_GPIO_Init(); MX_DMA_Init(); MX_ADC1_Init(); /* USER CODE BEGIN 2 */ HAL_ADC_Start_DMA (&hadc1, (uint32_t *) adc_buf, 2); /* USER CODE END 2 */ /* Infinite loop */ /* USER CODE BEGIN WHILE */ while (1) { /* USER CODE END WHILE */ /* USER CODE BEGIN 3 */ display_value[0] = adc_val[0]; display_value[1] = adc_val[1]; HAL_Delay (1000); } /* USER CODE END 3 */ } /* ADC1 init function */ static void MX_ADC1_Init(void) { ADC_ChannelConfTypeDef sConfig; /**Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion) */ hadc1.Instance = ADC1; hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4; hadc1.Init.Resolution = ADC_RESOLUTION_12B; hadc1.Init.ScanConvMode = ENABLE; hadc1.Init.ContinuousConvMode = ENABLE; hadc1.Init.DiscontinuousConvMode = DISABLE; hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE; hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START; hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT; hadc1.Init.NbrOfConversion = 2; hadc1.Init.DMAContinuousRequests = ENABLE; hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV; if (HAL_ADC_Init(&hadc1) != HAL_OK) { Error_Handler(); } /**Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time. */ sConfig.Channel = ADC_CHANNEL_0; sConfig.Rank = 1; sConfig.SamplingTime = ADC_SAMPLETIME_480CYCLES; if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK) { Error_Handler(); } /**Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time. */ sConfig.Channel = ADC_CHANNEL_TEMPSENSOR; sConfig.Rank = 2; if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK) { Error_Handler(); } } /** * Enable DMA controller clock */ static void MX_DMA_Init(void) { /* DMA controller clock enable */ __HAL_RCC_DMA2_CLK_ENABLE(); /* DMA interrupt init */ /* DMA2_Stream0_IRQn interrupt configuration */ HAL_NVIC_SetPriority(DMA2_Stream0_IRQn, 0, 0); HAL_NVIC_EnableIRQ(DMA2_Stream0_IRQn); } /** Configure pins as * Analog * Input * Output * EVENT_OUT * EXTI */ static void MX_GPIO_Init(void) { /* GPIO Ports Clock Enable */ __HAL_RCC_GPIOH_CLK_ENABLE(); __HAL_RCC_GPIOA_CLK_ENABLE(); } |
