Hi @fpistm, thank you for the detailed first review.

1. The Seeed XIAO STM32C5 is currently in the DVT stage and is planned for public launch in September, so there is no public product page available yet. I will share the official board link once it is published.

2. I have pushed an update addressing your comments: the USB HAL v2 adapter has been generalized, the USB definitions were moved to the common layer, the board menus now follow the existing core conventions, and the SPI3 MOSI alternate-function name was updated. Could you please check whether this now matches your expectations?

3. Regarding the SPI initialization regression, I saw that you have opened fix(spi): init never called at begin #3049, which addresses the same root cause. I have removed the board-specific SPI workaround from this PR, so I believe a separate issue is no longer needed. Please let me know if you would still prefer one.

Hi, thanks for the update.
and yes an issue for the SPI would help to track it.

As the board is not yet available. It would be fine to keep here only the board support addition and open separate PR for specific feature. I will try on my side and a Nucleo C562RE

Hi @fpistm, understood. I will open an issue for this.

Although the board does not yet have a public product page, I can provide test reports to demonstrate the product and its validation status. Our product manager is working to ensure Arduino platform support is ready as early as possible for our users.

If helpful, I would be glad to share this information with you. The current planned public launch date is August 29.

Thank you very much for your support.

I also noticed that the CI workflows for the latest update are awaiting approval. Could you please approve them when convenient, so the checks can run? :)

Thanks for the update. Will check this tomorrow.

Hello@fpistm, could you please check it? Our board is approaching the release date. Thank you. :）

Hi @cumin777
As said I have to check deeply and like split PR.

Hi @cumin777
Could you split the PR per feature?
In thios PR only the board support should be available.

Hi @fpistm, sorry for the delayed follow-up. I was handling other release-related work and did not track the PR closely enough. Thank you for the guidance.

I have now split the changes as requested:

• feat(xiao): add Seeed XIAO STM32C5 board support #3048 now contains only the Seeed XIAO STM32C5 board support (board definition, variant, linker script and board-level pin/menu configuration).
• The shared STM32C5 HAL v2 USB device support is now in feat(usb): add STM32C5 HAL v2 USB device support #3059 for separate review. For this first split, I kept the current PA_12 detach sequence in usbd_if.c; I would appreciate your advice on a more generic approach and can revise that PR accordingly.

I will continue separating any remaining shared functionality into focused PRs. Thank you for your patience and for reviewing this work.

Follow-up on the split: #3060 now contains the independent HAL v2 UART helper compatibility fix, and #3061 contains the generic UF2 upload recipe. #3048 remains board-only. The XIAO C5 UF2 upload path uses #3061 plus the uf2upload executable from Arduino_Tools #122; end-to-end CDC 1200-bps touch also requires the USB support in #3059. #3060 is independent of the USB, UF2, and Arduino_Tools PRs.

Updated the board-only PR with the physical BOOT0/user button from the latest board definition: PH2 is now exposed as an additional Arduino digital pin, and the standard STM32 core B1_BTN/USER_BTN macros map to it. The button is active-low in normal operation; because it is also BOOT0, holding it during reset/power-on may affect boot selection.

However, during my actual testing, even when I pressed the boot button and reset it, I was unable to trigger the built-in boot mode of the STM32. This also happened when we used the NUCLEO-C5A3ZG board. I'm not sure if this is a bug or if my usage method is incorrect.