Efficient, reliable and safe open source solution for serial communication

Hello everyone , I'm wheat .

In embedded development , Serial communication is often used . Facing different application scenarios , Different solutions are needed .

Today, let's talk about efficiency , reliable , A safe solution , Remember to see the end , There will be gains .

Common are serial port polling mode , Serial port interrupt mode , A serial port DMA Receive, transmit, etc ;

Using serial port Idle interrupt coordination DMA Ring buffer mode , It can efficiently receive messages with variable length

In the figure below, after the Yellow high-level time is idle , An idle event will be generated ,IDLE EVENT

Idle signal

because DMA Functions include HC and TC interrupt ;

• HC  （Harf Complete）DMA Transmission half success flag ;

• TC   (Total Complete)  DMA Transmission completion success flag ;

for instance ;

As shown in the figure below , There's a... Assigned here DMA buffer , Size is 12 byte , If from the address 1 Start receiving , There will be the following two situations ;

• DMA Received a second message 6 Bytes When , Will trigger HC event ;

• DMA Received The first 12 Bytes When , Will trigger TC event ;

HC TC

In fact, I have practiced this idea before , But they didn't make good use of HC and TC event .

So I can't handle this situation , namely DMA The buffer is in ring mode （Circular） When , The problem of data coverage , Recently I saw a great open source project , The idea here is very good , I'll give you a detailed introduction .

Here is DMA HC/DMA TC/Idle Details of serial port reception by combination , As shown in the figure below ;

From the original project

Again, briefly introduce the meaning of abbreviations ;

• R Read ;

• W write in ;

• I Idle signal ;

• HT Half-Transfer complete DMA Buffer half transfer complete ;

• TC Transfer-Complete DMA Buffer all receive complete ;

Here is a brief introduction situation E Solutions for , The small picture on the far right of the picture above ;

• Buffer size 20 grid , It is assumed that 20 byte , situation E Need to receive 30 Bytes , in other words ,10 Bytes may be overwritten ;

• After the first four receptions , The serial port continues from Letter R Receive data to DMA buffer ;

• receive 4 Byte time , Will trigger TC event , At this time, you can 4 Byte data processing ;

  
  First step

• Because it's a ring pattern , So go back to the first byte , Continue to receive 10 byte , Trigger HT event , You can deal with 10 Bytes of data ;

  
  The second step

• The third step , Continue to receive 10 byte , Trigger TC event , among , There has been a 4 Bytes are overwritten （ The following figure is shown in orange ）, Because this part of the data has been processed before , therefore , Even coverage does not affect ;

  
  The third step

• Step four , The above has been received 24 Bytes , So there are 6 Bytes not received , Later reception will generate idle signal , And cover the previous data area , As shown in the figure below ;

therefore , It's not hard to find out , If only idle interrupts are used , The length of the received buffer is greater than the required data , There will be data coverage , And add DMA Of HT and TC interrupt , It perfectly solves such a problem ;

Except for that, of course , There are many excellent schemes , This project provides a large number of examples .

Project address ：https://github.com/MaJerle/stm32-usart-uart-dma-rx-tx

Project home page

At present, this project mainly supports mainstream STM32 Testing on chip platform and some development boards DEMO, The details are as follows ;

Support platform

The corresponding example program is as follows , In addition to bare metal programs , There is also a ring buffer to receive , Polling reception ,DMA+ Idle interrupts are based on RTOS Mode reception , It's rich , You can refer to it ;

Example program

The author in STM32F413-Nucleo The development board tests the program , Found that the optimization effect is very good ;

stay 115200 Baud rate of serial port , Send... Every second 1581 Bytes , about 142ms;

• Don't use DMA,CPU load 14%;

• Use DMA,CPU load 0%;

Last , This project is currently based on STM32CubeIDE Created , Remember to set up an environment . If you can't download , Official account back office reply 【 High efficiency serial port 】 Get project code .

Enjoy  : )

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