STM32H750 DMA HAL_UART_Receive_DMA acting oddly

[da66en]

This is weird.  Also it was working at one point and stopped working, can't track down the code change that broke this.

So, I use HAL_UART_Receive_DMA() to start a DMA RX.  I can use _HAL_DMA_GET_COUNTER() to check how many characters have been received and I am receiving characters, but the contents of the buffer I passed to HAL_UART_Receive_DMA() is not changing.  Why would the DMA counter increase but not the memory buffer contents?  I checked the hdmarx handle in the UART handle, the Instance pointer in the hdamarx handle, and the MOAR and PAR pointers in the DMA peripheral - everything looks correct.

What more can I do to try to diagnose this problem?

Normal DMA (not circular), Peripheral to Memory.  Interrupt should be enabled but I don't think I need it with checking the buffer contents as it's received.

I got the idea to poll DMA contents while receiving from this blog post:

https://blog.stratifylabs.dev/device/2021-12-30-UART-FIFO-with-DMA-on-STM32/

And it worked for a while until something in the code broke.

This is a program with TouchGFX and it has always been trouble, just stuff in the HAL randomly breaking that has worked before. I currently have TouchGFX disabled right now.

[Pavel A. · Accepted solution]

> Why would the DMA counter increase but not the memory buffer contents? 

Mind the cache. Check that the destination memory address can be accessed by the DMA.

[da66en]

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@Pavel A. wrote:

> Why would the DMA counter increase but not the memory buffer contents? 

Mind the cache. Check that the destination memory address can be accessed by the DMA.

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Thanks, I think it was this.  I also got a lot of help from this:

DMA is not working on STM32H7 devices - STMicroelectronics Community

I moved DMA buffers to a fixed location and made a new MPU region with cache disabled.