Getting started with DMA

Coming soon

This article explains what is DMA and how to use it through examples

1. What is DMA?

DMA stands for Direct Memory Access controller. It is a bus master and system peripheral. The DMA is is used in order to provide high-speed data transfer between peripherals and memory as well as memory to memory. Data can be quickly moved by DMA without any CPU actions. This keeps CPU resources free for other operations.
During this article, we will be using the STM32L476 Nucleo board.
This device embeds 2 DMAs: DMA1 and DMA2. Each channel is dedicated to managing memory access requests from one or more peripherals.
The two DMA controllers have 14 channels in total, each dedicated to managing memory access requests from one or more peripherals. Each has an arbiter for handling the priority between DMA requests.

DMA features	DMA1	DMA2
Number of regular channels	7	7

1.1. Objective

Learn how to setup DMA transfer in STM32CubeIDE
Create simple DMA memory to memory transfer from RAM to RAM and transfer with Interrupt

1.2. How to

Use CubeIDE and Generate Code with DMA
Learn how to setup the DMA in HAL
Verify the correct functionality by comparing transferred buffers

2. Create the project in STM32CubeIDE

'File > New > STM32 Project in main panel.

This example uses the NUCLEO-L476RG board.
Start by selecting the NUCLEO-L476RG board using the Board Selector as shown in the figure below:

In case you haven't downloaded the STM32L476 Cube library, it will be downloaded automatically. This however may take some time.
Save the project.

For DMA we don’t need to configure any pins

3. Memory to Memory Mode

The DMA channels may operate without being triggered by a request from a peripheral. This mode is called memory-to-memory mode, and is initiated by software.
Memory to Memory mode allows transfer from one address location to another without a hardware request.
Once the channel is configured and enabled, the transfer starts immediately.

Information

The memory-to-memory mode must not be used in circular mode.

File:Memory to memory.png

3.1. DMA process workflow summary

At the beginning of the main program the HAL_Init() function is called to reset all the peripherals, initialize the Flash interface and the systick.
Using HAL_DMA_Start() to start DMA transfer after the configuration of Source address and destination address and the Length of data to be transferred.
Using HAL_DMA_PollForTransfer() to poll for the end of current transfer, in this case a fixed Timeout can be configured by User depending from his application.

At the end of the transfer, it is recommended to handle the return values to be sure that program working as expected

HAL_OK : DMA transfer was successfully finished and data was transferred to destination without error.
HAL_ERROR : Error occurs during DMA transfer you use HAL_DMA_GetError for details what happened.
HAL_BUSY : DMA transfer in progress, user can only abort the transfer

3.2. DMA M2M Configuration

In order to run on maximum frequency, setup clock system

File:clock tree.png

Accéder à Pinout & Configuration > DMA >DMA1 Button Add.

File:final config DMA1.png

Select

MEMTOMEM DMA request : DMA1 Channel 1
Normal mode
Increment source and destination address
Byte data width

File:final DMA config 2.png

Check system DMA in system view :

File:System view DMA Config.png

Generate the code by pressing Ctrl + S :
Open main.c in Project Explorer / myproject / Src / main.c.
Create two buffers : one foe the source data and the second as destination buffer
Insert the following lines between /* USER CODE BEGIN 0 */ and /* USER CODE END 0 */

/* USER CODE BEGIN 0 */
uint8_t Buffer_Src[]={0,1,2,3,4,5,6,7,8,9};
uint8_t Buffer_Dest[10];
/* USER CODE END 0 */

Now Insert the following lines between /* USER CODE BEGIN 2 */ and /* USER CODE END 2 */

/* USER CODE BEGIN 2 */
  HAL_DMA_Start(&hdma_memtomem_dma1_channel1, (uint32_t) (Buffer_Src), (uint32_t) (Buffer_Dest), 10);
    while(HAL_DMA_PollForTransfer(&hdma_memtomem_dma1_channel1, HAL_DMA_FULL_TRANSFER, 100) != HAL_OK)
    {
      __NOP();
    }
  /* USER CODE END 2 */

4. Memory to Memory transfer with Interrupt

To configure the DMA with Interrupt, follow the same steps in the previous paragraph " Memory to Memory Mode"
Configure the DMA1 Channel 1 Global Interrupt In System Core > NVIC as shown in the figure below :

Now generate the code by pressing : Ctrl + S

4.1. HAL Library DMA with IT flow

DMA intializations is generated in main.c
HAL_DMA_Start_IT : Start DMA buffer transfer
DMA1_Channel1_IRQHandler is generated in stm32f4xx_it.c : it indicates whether DMA process is half/complete or error was detected.
HAL_DMA_IRQHandler is defined in stm32f4xx_hal_dma.c : Process interrupt information.
DMA_XferCpltCallback : Data correctly transferred complete callback function.
DMA_XferErrorCallback : Error was detected Error callback function.

4.2. DMA M2M with IT Configuration

We will be using the same code as in DMA M2M Configuration.

Between /* USER CODE BEGIN 0 */ and /* USER CODE END 0 */ tags add :

void XferCpltCallback(DMA_HandleTypeDef *hdma);

Between /* USER CODE BEGIN 4 */ and /* USER CODE END 4 */ tags add :

/* USER CODE BEGIN 4 */
void XferCpltCallback(DMA_HandleTypeDef *hdma)
{
  __NOP();//we reach this only if DMA transfer was correct
}
/* USER CODE END 4 */

Before we start the DMA with interrupt we need to set the callback into DMA structure Then it is possible to use the HAL_DMA_Start_IT to begin DMA transfer

Between /* USER CODE BEGIN 2*/ and /* USER CODE END 2 */ tags add :

/* USER CODE BEGIN 2 */
  hdma_memtomem_dma1_Channel1.XferCpltCallback=&XferCpltCallback;
  HAL_DMA_Start_IT(&hdma_memtomem_dma1_Channel1,(uint32_t)Buffer_Src,(uint32_t)Buffer_Dest,10);
  /* USER CODE END 2 */

[[category:Getting_started_with_STM32_system_peripherals | 30]]