Re: Persistent USB serial?
- In reply to: Daniel Ebdrup Jensen : "Re: Persistent USB serial?"
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Date: Fri, 08 Oct 2021 07:34:13 UTC
On Fri, 8 Oct 2021 09:25:37 +0200 Daniel Ebdrup Jensen <debdrup@FreeBSD.org> wrote: > 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 Thanks for pointer, I'll try to evaluate. This does not give me a full solution, if I understand it right - I can have some unique name for a given USB serial port instance, but I still must write my command to attach to this port quickly in order to not miss first characters sent over this port, right? Regards, Milan