UART Async API support for STM32 Discovery Board

[rt-2pm2]

Hi Everyone,

Before opening a formal issue, I wanted to know if someone had some problem running the UART async API sample on a STM32.

I am trying to run the sample on a STM32 Discovery Board and I am getting an error at the point where the transmission request is issued. Precisely, the uart_tx() returns a -19 code for ENODEV.

For example, on an digital analyzer I see something like:

[00:00:05.000,000] \x1B[0m<inf> sample: Loop 0: Sending 3 packets\x1B[0m
[00:00:05.000,000] \x1B[1;31m<err> sample: Unknown error (-19)\x1B[0m
[00:00:05.000,000] \x1B[1;31m<err> sample: Unknown error (-19)\x1B[0m
[00:00:05.000,000] \x1B[1;31m<err> sample: Unknown error (-19)\x1B[0m
[00:00:05.000,000] \x1B[0m<inf> sample: RX is now enabled\x1B[0m

Best

Step to reproduce

1. Compile

west build -b stm32f4_disco samples/drivers/uart/async_api

2. Flash

west flash --runner openocd 

[ldomaigne]

I don't have the stm32f4_disco available, so I went for a nucleo_f411re instead.
Getting the async UART working for the STM32F4 boards isn't as straightforward as for the Nordic boards.
In particular, you need to configure DMA.
But the UART Async API sample should work fine.

In my case, I used USART1, mapped on PB_6 & PB_7.
USART2 is the default uart, so I needed to change zephyr,shell-uart accordingly.

As you might see with Kconfig search / menuconfig, the UART_ASYNC_API requires DMA to be configured for the STM32 boards.
So, I had to enable the DMA controller (dma2 in my case), and overlay the USART1 node to configure DMA transfer.
Finally, I looped TX/RX using the appropriate PINs on the morpho header.

In my case, the devicetree overlays looks like this:

/{
        chosen {
                zephyr,console=&usart2;
                zephyr,shell-uart = &usart1;
        };
};

&dma2 {
        status = "okay";
};

&usart1 {
        dmas =  <&dma2 7 4 STM32_DMA_PERIPH_TX STM32_DMA_FIFO_FULL>,
                <&dma2 2 4 STM32_DMA_PERIPH_RX STM32_DMA_FIFO_FULL>;
        dma-names = "tx", "rx";
};

Please check your board/Soc reference manual for the exact DMA configuration. See Related discussion.

Hope this helps!