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List:       linux-usb-users
Subject:    Re: [Linux-usb-users] USB host-to-host console
From:       Rogier Wolff <R.E.Wolff () BitWizard ! nl>
Date:       2007-08-21 11:53:46
Message-ID: 20070821115345.GB20551 () bitwizard ! nl
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On Mon, Aug 20, 2007 at 12:09:12PM +0200, Clemens Koller wrote:
> David Turvene schrieb:
> > On Sat, 2007-08-18 at 21:55 +0200, Guennadi Liakhovetski wrote:
> >>> What are my hardware/software/configuration options for local comms
> >>> (primary ethernet network down) between my laptop with only USB ports to
> >>> a headless server with only USB ports?
> >> Your another option would be to provide each your server with a 
> >> USB-to-serial dongle similar to the one you use with your laptop, and 
> >> specify "console=ttyUSB0,..." on server's kommand line (if you want a 
> >> console on it) and start a getty on it from /etc/inittab just as usual.
> >>
> >> Thanks
> >> Guennadi
> > 
> > 
> > Thanks for the reply.  That seems to be a good solution - effectively
> > two back-to-back USB-serial cables (e.g. what I use now, a Belkin
> > F5U109).  It seems so obvious with the pervasiveness of USB that I am
> > concerned about the seeming lack of implementations (at least there is
> > little in the HOWTOs and newsgroups).  Am I missing something?  I have a
> > hard time believing there are small server sites that do not have this
> > issue.
> > 
> > Maybe a PPP connection over USB is the preferred solution?  I have done
> > this with a PDA (Intel PXA255) but that contains a gadget controller.
> 
> There is something like a USB "Communication Device Class" (CDC) which
> should allow you to implement a serial console without the need for a RS232
> physical layer of all the USB-serial converters (FTDI, Keyspan, ...).

The problem with all these is that servers-with-uarts usually also 
allow their BIOS to be controlled from the UART. Similarly, your boot
program also supports control via the UART.

So, as long as your server boots, and gets to start up the USB layer,
you're fine. Anything goes wrong before that, and you're still stuck. 


>From a more or less theoretical point of view, if there had been an
"USB display device",  that was standard, then the BIOS might support
such a thing, and your computer could control this from the other end, 
together with an USB keyboard..... However, I don't see how to get the
video out of a "doesn't have serial" server, to diagnose and fix boot 
problems. 

	Roger.

-- 
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
**    Delftechpark 26 2628 XH  Delft, The Netherlands. KVK: 27239233    **
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