Subject: Re: This is my console and this is my other console
To: None <tech-kern@NetBSD.ORG>
From: der Mouse <mouse@Holo.Rodents.Montreal.QC.CA>
List: tech-kern
Date: 01/21/1997 19:05:43
>> when units of the device are 'attach'ed, if they're the console
>> device (there can be only one! 8-)

> Some machines have more than one console.  (Pyramid, and, uh, oh
> yeah, Sequent spring to mind)  Typically the 2nd console is connected
> to a modem and when there is a problem you enable the "remote"
> console, Service dials in and assists.  Both ports accept keyboard
> input and output goes to both screens.

Not that I wish to represent it as a general solution, but if both
consoles are serial lines (as in the modem-and-dumb-terminal case), you
can fake it with three connectors and some wires.  (To do it right you
really need two diodes and at least one pullup resistor, but I've had
it work just wiring the lines together.)  Of course, if both the
transmitters try to send characters timed such that they overlap on the
wire, you will a framing error or corrupted data.  (Assuming a
reasonably high baud rate and human typing speeds, the duty cycle will
be low enough that this is fairly unlikely to be a problem, even when
both humans are typing at the same time.  At 9600 baud characters are
a shade over 1ms wide, and even fast typists rarely generate much more
than 10cps sustained (120wpm is a good clip); if we round these off to
1ms and 10cps, the duty cycle works out to 1%.)

					der Mouse

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