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This article mainly shows you "STM32 how to use DMA to receive serial data", the content is easy to understand, clear, hope to help you solve doubts, the following let Xiaobian lead you to study and learn "STM32 how to use DMA to receive serial data" this article.

01. Overview

In the article explained by serial port, the sample code uses interrupt mode to receive and send data. the advantage of interrupt is that it can respond in time and receive data quickly, but the disadvantage is also obvious, that is, frequent interrupts. Receiving 1000 bytes requires 1000 interrupts, which means interrupting the execution of other code, which is not allowed in some application scenarios. At this time, the combination of DMA+ serial port can solve this problem very well.

DMA has 8 channels for each data flow, and each channel is mapped to different peripherals, which helps to configure different DMA peripheral requests for different products.

Each data flow can only be configured to map to one channel, not to multiple channels. That is, unlike data flow, each DMA controller can configure multiple data streams at the same time (because there is an arbiter), but each data flow cannot be configured with multiple channels at the same time (because there are only selectors).

We use USART1 serial port peripherals, and we can find out from the data manual that the sending and receiving of USART1 supports DMA, using DMA2.

Next, we will gradually understand the application of DMA in serial port.

02. DMA reception

We first configure DMA to link the DMA peripherals with the serial port. First, you need to configure DMA.

DMA configuration is no longer explained in detail, students who do not quite understand, please see the article "STM32DMA detailed explanation", here we directly paste the code.

Void DMA_Config (void) {DMA_InitTypeDef DMA_InitStructure; / * Enable DMA clock * / RCC_AHB1PeriphClockCmd (RCC_AHB1Periph_DMA2, ENABLE); / * Reset DMA Stream registers (for debug purpose) * / DMA_DeInit (DMA2_Stream2); / * Check if the DMA Stream is disabled before enabling it. Note that this step is useful when the same Stream is used multiple times: enabled, then disabled then re-enabled... In this case, the DMA Stream disable will be effective only at the end of the ongoing data transfer and it will not be possible to re-configure it before making sure that the Enable bit has been cleared by hardware. If the Stream is used only once, this step might be bypassed. * / while (DMA_GetCmdStatus (DMA2_Stream2)! = DISABLE) {} / * Configure DMA Stream * / DMA_InitStructure.DMA_Channel = DMA_Channel_4; / / DMA request to issue a channel DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t) & USART1- > DR;// configuration peripheral address DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t) UART_Buffer;// configuration memory address DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory / / Transmission direction configuration DMA_InitStructure.DMA_BufferSize = (uint32_t) 32 beat / transmission size DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;// peripheral address unchanged DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;//memory address increment DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;// peripheral address data unit DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte / / memory address data unit DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;//DMA mode: normal mode DMA_InitStructure.DMA_Priority = DMA_Priority_High;// priority: high DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;//FIFO mode is not enabled. DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_Full;// FIFO threshold selection DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;// memory burst mode selection, optional single mode, 4-beat incremental burst mode, 8-beat incremental burst mode or 16-beat incremental burst mode. DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;// peripheral burst mode selection, optional single mode, 4-beat incremental burst mode, 8-beat incremental burst mode or 16-beat incremental burst mode. DMA_Init (DMA2_Stream2, & DMA_InitStructure); / * DMA Stream enable * / DMA_Cmd (DMA2_Stream2, ENABLE);}

In addition to configuring DMA peripherals, we also need to configure the DMA configuration corresponding to the serial port, which is explained in a small chapter in the manual.

The register that needs to be configured is the USART_CR3 register.

We can configure the bit6 and bit7 of the USART_CR3 register to enable the serial port to send and receive DMA. The standard peripheral library of ST also provides the corresponding peripheral library.

Void USART_DMACmd (USART_TypeDef* USARTx, uint16_t USART_DMAReq, FunctionalState NewState)

The DMA configuration of the serial port can be configured through the above interface as follows:

/ * enable serial port DMA to receive * / USART_DMACmd (USART1, USART_DMAReq_Rx, ENABLE); 03. Interrupt

We use DMA+ serial port to solve the problem of frequent interruptions, but now there is a problem, we also need to inform CPU of the received data information in time in order to achieve the timeliness of the data. We use two peripherals, DMA and serial port, and they all have their own interrupts.

Using DMA interrupts, configure as follows

/ * Enable DMA Stream Transfer Complete interrupt * / DMA_ITConfig (DMA2_Stream2, DMA_IT_TC, ENABLE); / * Enable the DMA Stream IRQChannel * / NVIC_InitStructure.NVIC_IRQChannel = DMA2_Stream2_IRQn;NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0 / ENABLE;NVIC_Init (& NVIC_InitStructure)

When the DMA is received, an interrupt will be generated to inform the CPU to fetch data.

But there is an obvious defect: if the serial port receives a packet of data, if the length is less than the buffer length of the DMA, the interrupt can not be triggered for a long time, and the interrupt will not occur until the DMA receives the full data. If the next packet of data is delayed, then the packet can not be responded in time.

Then we use serial port interrupt is a good solution. The serial port provides an idle interrupt, which "seems" to be used specifically for DMA.

When the serial port receives a packet of data, after receiving the last byte, when there is no data reception, there will be an interrupt, at this time, CPU can take the data.

The configuration knowledge of serial port is no longer explained. For students who do not quite understand, please see "detailed explanation of STM32 serial port". The configuration of idle interrupt of serial port is as follows.

USART_ITConfig (USART1, USART_IT_IDLE, ENABLE); / * Enable the USARTx Interrupt * / NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0; NVICS IRQChannelSubpriority = 0; NVICmatters IRQChannelCmd = ENABLE;NVIC_Init (& NVIC_InitStructure)

The serial port interrupt code is as follows

Void USART1_IRQHandler (void) {uint8_t temp; if (USART_GetFlagStatus (USART1, USART_FLAG_IDLE) = = SET) {DealWith_UartData (); / / USART_ClearFlag (USART1, USART_FLAG_IDLE); temp = USART1- > SR; temp = USART1- > DR; / / clear USART _ IT_IDLE flag}}

Point: there is a pit here!

The code to clear idle break bits is

Temp = USART1- > SR; temp = USART1- > DR; / / clear the USART _ IT_IDLE flag

The evidence is as follows

This is very deceptive. Pay attention.

The above is all the contents of the article "how to use DMA to receive serial port data in STM32". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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