HAL_UART_Transmit_DMA(), only works with inline defined string and fails with globaly defined array

why does this work:

HAL_UART_Transmit_DMA(&huart6, (uint8_t *)"stm32\n", 6); // works and sends data

and this doesnt:

ALIGN_32BYTES (uint8_t aTxBuffer[]) = "stm32\n";

HAL_UART_Transmit_DMA(&huart6, (uint8_t *)aTxBuffer, 6) // doesnt send any data

what am i missing?

This topic has been closed for replies.

Best answer by zhausq

solved! appreciate the quick responses, thank you!

for anyone whose reading this and having the same issue: this is what you're looking for https://community.st.com/s/article/FAQ-DMA-is-not-working-on-STM32H7-devices

Graduate II

Most likely aTxBuffer is located in DTCM, to which only the MDMA has access in H7 series. Take a look at AN4891 figure 1.

Visitor II

DMA buffers must be located in (the appropriate) RAM. Fixed strings or other constant data are usually stored in ROM (flash).

You should verify/ensure that the data is provided on stack / RAM.

zhausqAuthorAnswer

Visitor II

solved! appreciate the quick responses, thank you!

for anyone whose reading this and having the same issue: this is what you're looking for https://community.st.com/s/article/FAQ-DMA-is-not-working-on-STM32H7-devices

Technical Moderator

Glad to know that your question is answered. Please mark the article as helpful in this case.

Thanks

Amel

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