STM32F3x DMA configuration for UART

[sbendt]

Hi,

I am trying to use the async transfers with usarts, but it fails to enable the UART (using uart_rx_enable), due to no DMA configured for the usart.

I have not been able to modify the device tree for DMA, but so far unsuccessful.

On the dma1 node, I have changed the status from "disabled" to "okay", and modified the usart3 to reference the dma1 in "dmas".

&dma1 {
status = "okay";
};

&usart3 {
pinctrl-0 = <&usart3_tx_pb10 &usart3_rx_pb11>;
pinctrl-names = "default";
current-speed = <19200>;
dmas = <&dma1 3 1 (STM32_DMA_PERIPH_TX | STM32_DMA_PRIORITY_HIGH)>,
<&dma2 2 1 (STM32_DMA_PERIPH_RX | STM32_DMA_PRIORITY_HIGH)>;
//dma-names = "tx", "rx";
status = "okay";
};

It fails with:
zephyr.dts:209.4-64: Warning (dmas_property): /soc/serial@40004800:dmas: cell 3 is not a phandle reference
zephyr.dts:209.4-64: Warning (dmas_property): /soc/serial@40004800:dmas: Could not get phandle node for (cell 3)

The MCU is the STM32F303CBT6 .

Any idea how to configure DMA for usarts correctly?

[FRASTM]

Hello,

When using the usart3 with DMA
the dts should look like :

 &usart3 {
	...
	dmas = <&dma1 2 STM32_DMA_PERIPH_TX>,
		<&dma1 3 STM32_DMA_PERIPH_RX>;
	dma-names = "tx", "rx";
};

This is given by the table of the Ref Man for DMA1 request for each channel.

[FRASTM]

Running the tests/drivers/uart/uart_async_api for the usart3 on the corresponding board (connecting Tx to Rx pins) should PASS

[sbendt]

Thank you for the reply and information - appreciate it!

I did the modifications and I am able to enable the UART and get some of the events in the callback function. However, when transmitting data, the application crashes and I never get the UART_RX_RDY event. I still have some debugging to do, but let me know if you have any recommendations or things to check.

[FRASTM]

did you try with current-speed = <115200>;

[sbendt]

I got the receive part working, but for some reason transmit crashes my application.

The error handler k_sys_fatal_error_handler is called with reason=26 initially and then reason=4 after.

I am not sure how to troubleshoot that.

&dma1 {
status = "okay";
};

&usart2 {
pinctrl-0 = <&usart2_tx_pa2 &usart2_rx_pa3>;
pinctrl-names = "default";
current-speed = <115200>;
dmas = <&dma1 7 (STM32_DMA_PERIPH_TX | STM32_DMA_PRIORITY_HIGH)>,
<&dma1 6 (STM32_DMA_PERIPH_RX | STM32_DMA_PRIORITY_HIGH)>;
dma-names = "tx", "rx";
status = "okay";
};

The channel 6 and 7 should be in accordance with the manual.

[R-Lourens]

@sbendt Hello, I am also looking to implement uart using the Zephyr async api. My board is a STM32F3 Nucleo-144. So far this discussion has helped me alot but I would like to know if you are willing to share how your code looks in your main.c file? (This is my first time working on DMA's) I have looked at https://github.com/zephyrproject-rtos/zephyr/tree/main/tests/drivers/uart/uart_async_api and I think that I could figure out how to use the async api from there also?