STM32F4 DMA

### STM32F4 DMA Configuration and Usage Examples #### Overview of DMA on STM32F4 Microcontrollers Direct Memory Access (DMA) allows data transfer between memory areas or between peripherals and memory without CPU intervention, improving system efficiency by offloading the processor from handling these transfers. On STM32F4 series microcontrollers, multiple DMA controllers are available to manage different types of transactions efficiently. #### Configuring DMA Channels To configure a DMA channel for use with an application, several parameters must be set up properly: - **Stream Selection**: Choose which stream will handle the transaction. - **Channel Selection**: Selects one out of eight possible channels per stream. - **Priority Level**: Sets how urgent this particular request is compared to others. - **Transfer Direction**: Specifies whether it's peripheral-to-memory, memory-to-peripheral, etc. - **Circular Mode Enable/Disable** - **Data Size & Increment Settings** For example, configuring UART communication using DMA involves setting appropriate values as shown below[^1]: ```c /* Configure the DMA handler for reception process */ hdma_usart_rx.Instance = DMA_STREAM; hdma_usart_rx.Init.Channel = DMA_CHANNEL; hdma_usart_rx.Init.Direction = DMA_PERIPH_TO_MEMORY; hdma_usart_rx.Init.PeriphInc = DMA_PINC_DISABLE; hdma_usart_rx.Init.MemInc = DMA_MINC_ENABLE; hdma_usart_rx.Init.PeriphDataAlignment = DMA_PDATAALIGN_BYTE; hdma_usart_rx.Init.MemDataAlignment = DMA_MDATAALIGN_BYTE; hdma_usart_rx.Init.Mode = DMA_CIRCULAR; hdma_usart_rx.Init.Priority = DMA_PRIORITY_HIGH; if (HAL_DMA_Init(&hdma_usart_rx) != HAL_OK) { /* Initialization Error */ } ``` This code snippet initializes a DMA instance specifically tailored towards receiving serial data through USART interface in circular mode at high priority level while ensuring byte alignment during both source and destination operations. #### Example Code Demonstrating Basic Functionality Below demonstrates basic functionality where ADC conversion results get transferred directly into RAM buffer via DMA automatically after each sample completion event occurs within hardware timer interrupt service routine context[^2]. ```c // Initialize ADC and DMA structures here... while(1){ // Start continuous conversions... __HAL_ADC_START_IT(&hadc); } void TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim){ static uint8_t counter=0; if(counter++>=SAMPLES_COUNT){ // Stop ADC/DMA when enough samples collected __HAL_ADC_STOP(&hadc); HAL_DMA_DeInit(hdma_adc); ProcessSamples(buffer,SAMPLES_COUNT); counter=0; } } ``` In this scenario, once all required number of analog readings have been gathered inside `buffer`, processing can occur outside critical sections thus freeing main loop resources significantly.