Re: Persistent USB serial?

On Fri, Oct 08, 2021 at 08:00:16AM +0200, Milan Obuch wrote:
>Hi,
>
>I'd like to solicit opinions/hints for following scenario, which is
>quite common currently.
>
>There are some development and evaluation boards designed with USB port
>as power source and serial console at the same time (sometimes even
>more ports or JTAG as well). When board has power on switch, usually no
>activity is present on USB wire without board being powered - there is
>some USB-to-UART circuitry powered from board power source. So serial
>port device /dev/cuaUn et al. get created only after power on of the
>board.
>
>Problem: port number can be different depending on USB port enumeration
>or connection order. Another one: it is easy to miss first characters
>sent from the board if you are not able to write required command like
>'cu -l /dev/cuaU9 -s 115200' quickly.
>
>Maybe it is possible to write some devd config file snippet which
>ensures consistent device naming without need of maintaining correct
>(everytime the same) order of cable connecting, but even that, this
>does not solve second problem, starting up some terminal or terminal
>like program in time.
>
>Has anybody some experience in this area who can share it? Some hints
>what to test? Do we have some pseudo serial device, which can be used
>as device argument for cu command, which can just grab the real USB
>serial when it appears on connecting the board under test?
>
>Regards,
>Milan
>

Hi Milan,

      There's an open review [1] for location-based unit numbering for
      USB, which some of us have been using for quite some time - and
      while it's not completely done, it's very useful.

Yours,
Daniel Ebdrup Jensen

1: https://reviews.freebsd.org/D21886