[riot-notifications] [RIOT-OS/RIOT] boards: add support for nrf52840-dongle (#13146)

chrysn notifications at github.com
Fri May 8 12:06:37 CEST 2020

> > I opine that the baud-rate-to-bootloader should be limited to boards that do this with the vendor SDK,
> But why? This is a feature of the nrfutil bootloader, why not use it - does it cost much ROM?

The feature of nrfutil bootloader is having a reset-into-bootloader. I'd be happy to review an API proposal for that, and it wouldn't cost ROM unless used.

The baud-rate-to-reset doesn't cost much ROM, but it's abusing a well-defined USB interface as a transport for something that is not announced in USB descriptors. It's that kind of by-convention stuff that gets us problems with modemmanager heuristics probing ports "for maybe this is a modem even though it doesn't advertise itself as heuristics".

If it needs be, we can have the discussion of whether this should be default for all RIOT devices (right now AFAICT it's only for devices where this is the method advertised with the board and its vendor SDK), but please let's not have that right here but then in a generic discussion.

> > The main issue is to know what is the magic number or strategy that makes the nrfutil bootloader to stay in bootloader mode.
> My guess would be that it's the same for all nrfutil bootloaders

Probably. But that's for implementing the reset function which only has the very ad-hoc `usb_board_reset_in_bootloader` API that's not even defined anywhere yet, and I don't think we should do in this step as it wouldn't be used in the first place. When we do (ie. there is a header file with documentation for the function, it's renamed from usb_board_reset_in_bootloader to something USB-unrelated and probably there'll be a command-line `bootloader` command that triggers it), then we can add this for this board.

Right now I'd like to get any conflict between this-board-being-built-for-nrfutil and build errors around riotboot out of the way.

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