[clue-tech] Need lots of help at Installfest

[Jed S. Baer]

On Fri, 15 May 2009 17:47:28 -0600 (MDT)
David L. Willson wrote:

> It's a DOD project.

Abandon all hope. ;-)

Uh, is that even a 2.n kernel? Even so, I suspect support for the 16550
UART will be there.

> Running in a VM is not an option.  Worse yet, the
> top priority is that the serial port must work.  The ~serial~ port?
> What?  I don't even know what to use one for, anymore, much less test
> it in Linux.

A serial port is useful for dialup networking, if your DSL or cable goes
down. What? You mean you don't keep an old 56K modem sitting around in a
box someplace?

My UPS communicates with my PC via serial port. Some years back, I had to
modify the UPS daemon serial init code, because for some reason it wanted
to "initalize" the serial port by repeatedly toggling DTR, which my UPS
took as a fault signal of some sort (I don't recall the gory details any
more). The Linux tty driver isn't as conventient as QIO calls, though.
(See, I can still reminisce about RSX.)

It's also useful for brain-dead console capture to another machine. You
tell your box that ttyS0 (or whatever it's called these days) is the
console, then hook up to another box using a null-modem cable. Run
minicom with logging on the other box to capture console output. I think
you can capture syslog this way too, if you want log capture on a machine
that isn't connected to the IP network.

Oh, and the above config is how you can test the serial port. Null modem
cable, 2nd box, minicom. I think I might have a null modem cable laying
about someplace, but I have a commitment keeping me from the installfest.

Oh, I suppose it's worth asking what sort of capability they want from the
serial port. If it's just simple comm with XON/XOFF flow control, that's
just 3 wires; TX, RX, GND. If they want RTS/CTS flow control, I'd have to
dig up how you cross the wires for a null-modem cable. Well, I'm sure
there's a web page out there somewhere with that info. I don't remember
how to deal with DTR/DSR either. Sometimes, a breakout box is good to
have.

Once you have basic comm working using minicom, you can test file xfers
using Kermit or Zmodem.

jed