DMA and UART not triggering completion INT sometimes

[mur]

Hi,

I'm using serial communication with DMA and sometimes the transmission complete interrupt is not triggered (HAL_UART_TxCpltCallback) the issue happens every few minutes, or every several hundred transmissions.

I saw https://community.st.com/s/question/0D50X00009XkfArSAJ/dmausart-on-stm32f407vg-tc-interrupt-sometimes-not-triggered and I think it may be related: I am putting variable length messages into the DMA and I wonder whether there's constraints in the length that can be set.

I have tested for some time now triying to find a pattern and in all cases the data packet length was pretty small, whenever the DMA stopped triggering the interrupt, the lengths were 17, 11, 5, 5, 3, 5 (6 different tests).

So the questoin is, is there any limitation in the data length to set into the DMA?

For sending, I'm using HAL's HAL_UART_Transmit_DMA()

Best regards.

[waclawek.jan]

The issue in the linked thread is related to FIFO. Do you use FIFO in DMA? Read out and post the DMA registers' content in case of problematic length.

JW

[mur]

I don't know, I'm using the automatic configuration from stm32cubeIDE. I know I'm using the DMA in Normal mode with an increment size of a byte.

I tried browsing for FIFO in the reference manual of my device (stm32f334r8, RM0364) and FIFO was only mentioned along DMA in the SPI section. Is it the same FIFO?

[waclawek.jan · Accepted solution]

The 'F3's DMA does not have FIFO.

There's no particular length limitation for USART/DMA. I believe it's coincidental that you see problems with odd lengths.

JW

[mur]

Indeed, the interrupt was not triggered because the transfer was not started. The source was a race condition in my code. Thanks for your time.

BR.

[waclawek.jan]

Thanks for coming back with the solution.

JW