Re: gpio pins -> tty/cua device

On Fri, Sep 20, 2024, 11:07 PM Bjoern A. Zeeb <
bzeeb-lists@lists.zabbadoz.net> wrote:

> On Fri, 20 Sep 2024, Warner Losh wrote:
>
> > On Fri, Sep 20, 2024, 10:49 PM Bjoern A. Zeeb <
> > bzeeb-lists@lists.zabbadoz.net> wrote:
> >
> >> Hi.
> >>
> >> I have one/two GPIO pins for RX/TX (possibly on two controllers) which
> >> on the other end have a serial console which I would love to read/wwrite
> >> to.
> >>
> >> Do we have any glue which takes two GPIO pins and present them as
> tty/cua
> >> device?
> >>
> >
> > No. We don't do serial emulation through software. You need high
> precision
> > timers paired with it to even start. And input bytes are way harder to
> get
> > right. Likely need a dedicated thread for any decent data rates. What
> speed
> > were you hoping for?
>
> Default of this thing is 115200 ; in theory it can be changed but
> probably not initially in my case today.
>
> Background is that some SFPs expose their (embedded u-boot/Linux) serial
> console on two PINs (which may be overlayed with other SFF functionality
> which makes this all tricky).
>
> I am just trying to find a way for remote debugging without hands on
> given one of the SFPs went haywire.
>
>
> So more helpful if future HW revisions would have these pins on a header
> and a USB adapter could be attached or if they were alternatively routed
> to an intenral UART of the SoC and one could switch them back and forth
> or something?
>


Many SoCs have pinmux. Maybe you're lucky and the pins you want to use can
be muxed via FDT changes to a UART, which makes things suddenly easy.

Warner

/bz
>
> --
> Bjoern A. Zeeb                                                     r15:7