Скачать или смотреть Implementing UART Receive with DMA on STM32F4-Discovery: How to Use Start and End Markers

Discover how to effectively read strings via UART using DMA on STM32F4-Discovery while implementing start and end markers for data processing.
---
This video is based on the question https://stackoverflow.com/q/64629799/ asked by the user 'Tea' ( https://stackoverflow.com/u/11152150/ ) and on the answer https://stackoverflow.com/a/64633963/ provided by the user 'kkrambo' ( https://stackoverflow.com/u/1401213/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: STM32F4-Discovery UART receive by DMA with included start-marker as well as an end-marker

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Reading Strings via UART with Start and End Markers Using DMA on STM32F4-Discovery

When dealing with embedded systems, especially when programming with platforms like the STM32F4-Discovery, interfacing the hardware with communication protocols like UART (Universal Asynchronous Receiver-Transmitter) can be daunting, especially for many beginners. In this post, we'll explore a common challenge: how to read strings into a DMA buffer while incorporating start and end markers.

The Problem

You might be trying to receive a string over UART, but only want to process the data that resides between specific markers - for example, you want to read data that is enclosed between the characters < and >. Moreover, you want to automatically call a function to process this data once the end marker is detected. This is a great feature for streamlining data handling in embedded applications.

The question you might have is: How can we effectively implement this feature using STM32Cube IDE?

Understanding DMA and UART

Before we dive into the solution, it’s essential to clarify two core components involved in this process:

DMA (Direct Memory Access): This peripheral allows hardware components to transfer data to and from memory without continuous CPU intervention, thus freeing up the processor for other tasks.

UART: This is a hardware communication protocol used for asynchronous serial communication, which involves the transmission of data in bytes.

The Solution

1. Limitations of DMA

While DMA is powerful, it has limitations. The critical point to understand here is that:

DMA cannot check the value of the data: DMA will continuously copy bytes to memory as they are received, but it doesn't have the capability to differentiate data based on delimiter values (like < and >).

2. Use CPU for Delimiter Checks

To work around this limitation, we can use the UART's RX interrupt alongside the DMA. Here’s how to structure the implementation:

Set up the UART with DMA: Initialize the UART for continuous data reception. This will allow data bytes to be written to a designated buffer.

Implement the RX Interrupt: Use an interrupt to check each received byte. This way, you can inspect each byte to see if it is a delimiter.

3. Pseudo Code Example

The overall flow of your code would look something like this:

[[See Video to Reveal this Text or Code Snippet]]

4. Key Considerations

Buffer management: Ensure that your buffer is adequately sized to handle maximum expected message lengths.

Handling continuous streams: If you're processing continuous streams of data, it might be helpful to implement a state machine or a similar logic structure to manage different states based on your start and end markers.

Conclusion

While it might seem challenging at first, using UART with DMA and incorporating start and end markers is entirely feasible. It requires a slight shift in approach by leveraging the CPU with UART interrupts to examine each byte, while DMA serves its purpose by facilitating the transfer of continuous data communication. By following the steps outlined in this guide, you can ensure efficient and effective processing of UART data utilizing DMA on your STM32F4-Discovery board.

With these insights, I hope you're now better equipped to implement your UART receiving solution. Happy coding!