DMA：USART

DMA：USARTHardware connectionControl principlePin definitionSoftware codeControl functionExperimental phenomenon

The tutorial demonstrates serial port (USART1) communication via DMA.


The tutorial only introduces the standard library project code

Hardware connection

Peripherals	Development board	Description
USART1_TX	PA9	USART1 sends data
USART1_RX	PA10	USART1 receives data

Control principle


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Serial port related knowledge will not be introduced, mainly DMA knowledge.

STM32F103RCT6 has two DMA controllers, DMA1 has 7 channels and DMA2 has 5 channels;

It is used for high-speed data transmission between peripherals and memory and between memory and memory.

DMA features

DMA initialization and startup are completed by the CPU, and the transfer process is performed by the DMA controller without CPU involvement, thus saving CPU resources for other operations.

DMA1 requests for each channel

DMA2 requests for each channel

This tutorial uses DMA1 channel 4.

Pin definition

Main control chip	Pin	Main function (after reset)	Default multiplexing function	Redefine function
STM32F103RCT6	PA9	PA9	USART1_TX/TIM1_CH2
STM32F103RCT6	PA10	PA10	USART1_RX/TIM1_CH3

Software code

Since the default function of the PA9/10 pin is a normal IO pin function, we need to use the multiplexing function.


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Product supporting data source code path: Attachment → Source code summary → 1.Base_Course → 15.USART+DMA

Control function

The tutorial only briefly introduces the code, and you can open the project source code to read it in detail.

uart_init


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void uart_init(u32 bound)
{
    //GPIO port settings
    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1|RCC_APB2Periph_GPIOA, ENABLE); //Enable USART1, GPIOA clock

    //USART1_TX GPIOA.9
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9; //PA.9
    GPIO_InitStructure.GPIO_Speed ••= GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; //Multiplex push-pull output
    GPIO_Init(GPIOA, &GPIO_InitStructure);//Initialize GPIOA.9

    //Initialize USART1_RX GPIOA.10
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;//PA10
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;//Floating input
    GPIO_Init(GPIOA, &GPIO_InitStructure);//Initialize GPIOA.10
    //USART initialization settings

    USART_InitStructure.USART_BaudRate = bound;//Serial port baud rate
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;//Word length is 8-bit data format
    USART_InitStructure.USART_StopBits = USART_StopBits_1;//One stop bit
    USART_InitStructure.USART_Parity = USART_Parity_No; //No parity bit
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None; //No hardware data flow control
    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx; //Transmit and receive mode

    USART_Init(USART1, &USART_InitStructure); //Initialize serial port 1
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE); //Serial port receive interrupt
    USART_Cmd(USART1, ENABLE); //Enable serial port 1

    NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1; NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; 
    NVIC_Init(&NVIC_InitStructure); 
    }

USARTx_DMA_Config


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void USARTx_DMA_Config(void)
{
    DMA_InitTypeDef DMA_InitStructure;

    // Enable serial port DMA clock
    RCC_AHBPeriphClockCmd(USART_TX_DMA_CLK, ENABLE);
    // Set DMA source address: serial port data register address*/
    DMA_InitStructure.DMA_PeripheralBaseAddr = USART_DR_ADDRESS;
    // Memory address (pointer to the variable to be transferred)
    DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)SendBuff;
    // Direction: from memory to peripherals
    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;

    // Transfer size
    DMA_InitStructure.DMA_BufferSize = SENDBUFF_SIZE;
    // Peripheral address does not increase
    DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    // Memory address increment
    DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
    // Peripheral data unit
    DMA_InitStructure.DMA_PeripheralDataSize =
    DMA_PeripheralDataSize_Byte;
    // Memory data unit
    DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;

    // DMA mode, one-time or circular mode
    DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;
    //DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
    // Priority: Medium
    DMA_InitStructure.DMA_Priority = DMA_Priority_Medium;
    // Disable memory-to-memory transfer
    DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
    // Configure DMA channel
    DMA_Init(USART_TX_DMA_CHANNEL, &DMA_InitStructure);
    // Clear the conversion flag of DMA1 channel 4
    DMA_ClearFlag(USART_TX_DMA_FLAG_TC );
    // Enable DMA
    DMA_Cmd (USART_TX_DMA_CHANNEL,ENABLE);
}

Experimental phenomenon

The USART_DMA.hex file generated by the project compilation is located in the OBJ folder of the [USART+DMA] project. Find the USART_DMA.hex file corresponding to the project and use the FlyMcu software to download the program to the development board.

After the program is successfully downloaded: Use the serial port debugging assistant to view the information, and you can see that the serial port prints Usart1 DMA Class! and Hello (Hello prints for about 300ms).


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When using the serial port debugging assistant, you need to pay attention to the serial port settings. If the settings are wrong, the phenomenon may be inconsistent