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po221
po221
Senior
May 12, 2020
Question

DMA to receive unknown length frames with UART

  • May 12, 2020
  • 4 replies
  • 3108 views

Hi

I need to listen to Rx UART to receive unknown length frames (I will search for a frame start byte, then read the frame size and then test a CRC for frame validating)

I would like to use DMA for performance but I only see half or full reception interrupt of a fixed number of bytes.

Is it possible to do that with DMA or must I using simple interrupts, with 1interrupt for each byte received ?

thanks in advance

PS : I'm using STM32L431 with STM32cubeIDE

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4 replies

waclawek.jan
waclawek.jan
Super User
May 12, 2020

Cube-based, although principle may be usable generally:

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

Author is ST FAE.

JW

po221
po221Author
Senior
May 12, 2020

Thanks a lot

I was reading this from the same author

https://stm32f4-discovery.net/2017/07/stm32-tutorial-efficiently-receive-uart-data-using-dma/

RMcCa
RMcCa
Senior II
May 12, 2020

Dunno about L4s, but F7s have a UART character match interrupt that i have used in conjunction with DMA. If you can terminate the messages with a unique framing character, this method works great. Just stop the DMA in the UART isr and read the NDTR​ and subtract from the initial value to find the number of bytes in the message.

po221
po221Author
Senior
May 12, 2020

L4 reference manual indicates CMIE Character match control bit.

I look for this solution too

Thanks

Tesla DeLorean
Tesla DeLorean
Guru
May 12, 2020

Depends if the pattern appears elsewhere in the data stream.

Personally found it easier to use a circular DMA buffer I can sweep on the 1 KHz ticker, or main loop

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RMcCa
RMcCa
Senior II
May 12, 2020

Thus the reason for the word 'unique' in my response. I use ascii hex to send user commands to my system partially for this reason. 0x0a can only happen at the end of a message. Using ascii hex effectively halves the actual transmission rate in exchange for robustness that is simple and efficient to implement.​

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