Serial Port Configuration

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I have a unique application that will require some creative
configuration of two serial ports on an embedded system. I haven't
chosen a target board yet so I'm open to recommendations (low power, 2
serial, and 2 Ethernet req'd).

On one serial port there will be a MODEM and on the other serial port
a device that is capable of dialing out. When I dial into the MODEM I
would like for the the embedded system to act as a Dial-In Server for
two other devices connected to the Ethernet ports. When the device on
the other serial port dials out I would like the embedded system to
"echo" or pass the serial communication through to the MODEM on the
other serial port.

So the embedded system will serve two functions.

1. Dial-In Server

2. "Serial Communication Valve" allowing unhindered communication in
one direction and using the opposite direction for the input to the
Dial-In Server.

Is this possible?

If so, how difficult?



Re: Serial Port Configuration
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Ok, some assumptions here.
The devices on the Ethernet (why 2? can't bare to use a switching hub?)
are TCP/IP. (?)
The device connected to the second (not modem) serial port needs to
"dial out", my question : is it a device that also uses TCP/IP (over PPP
for example) or is it just a "serial device" that would need to be
converted to TCP/IP ?

What you would want is mgetty running on the modem port along with pppd
and you would setup the routing in the linux part to route packets from
the ethenet devices to the network.

What type of comunications will the other devices be using?
What kind of machine will be dialing into the server?

Re: Serial Port Configuration

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Yes, both are TCP/IP. (One is AXIS2420 network camera and other is
SitePlayer (SP).... SP will also use UDP messages.)

I would like to eliminate the need for another piece of hardware in a
remote/solar powered system. I've found several target boards that
might work, Soekris 4501 or AXIS 82. I think the Soekris may be more
suitable for my newbishness since it won't require cross compilation. / / /

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TCP/IP....It can dial into an ISP. (Actually it is the AXIS2420
also....quite a confusing interconnection, but quite functional for
what I need to accomplish.)

Big Picture:

MODEM<--------->LINUX EMBEDDED<----------->AXIS2420
                   |       ^                   ^
                   |       |                   |
                   |       |___________________|

(The serial connection from the 2420 is for dialing out and the
Ethernet is for configuring by dialing into the LINUX EMBEDDED

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I'm currently working on a full size platform, learning Linux,
attempting the configuration that is obvious. I've found good info on
setting up a Dial-In Server, so that shouldn't be too difficult. The
question is...what is the terminology for what I want to do in the
other direction, i.e. have the Linux server echo the cameras serial
comms out the other serial port so it will be able to dial out?

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Do you need more than above?

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Remote PC....Win2K(just because I have the most experience...) box w/
dial-up connection. The embedded system will have a couple of html
pages to allow access to the SitePlayer and 2420.

Thanks for the help,


Re: Serial Port Configuration

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Ok, here me out on this...
Now from my limited knowledge of network cameras, the 2420 is probably
able to connect to a FTP server somewhere and drop pictures on it.
Why not, just have it drop the pictures onto the embedded linux device.
The embedded linux could run a script to dial out the modem and connect
to whatever when the pictures are present and upload them to the server
That eliminates the serial port connection to the 2420. Then with this
linux serial port open, you can connect it to whatever the siteplayer is
connected to (unless the siteplayer is designed into something, I don't
think you said what the function of the siteplayer was).

So you have
  MODEM<--serial-->LINUX EMBEDDED<--ethernet-->AXIS2420
        (whatever the siteplayer is connected to)

What am I missing?

Re: Serial Port Configuration
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       ^^^^- on second though, I am an idiot...maybe you shouldn't HEAR
me out.

Re: Serial Port Configuration

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I've thought of every different possible way to put this thing
The best way would be this:


And have the camera, which is already an embedded Linux server handle
the packet forwarding. BUT, I ruled that out because there is no
development support for the camera (unless you are a huge company.) It
is also a eLinux 2.0 kernel that won't handle modules, so I can't just
add PPP and anything else I might need.....)

The SitePlayer will be connected to a custom board with a PIC to
monitor and control the individual pieces in the system. I'm using the
SitePlayer to provide a web interface to the control and monitoring

I'm leaning towards the COTS solutions to minimize actual wrench
twisting in building the system.

I prefer the 2420 serial interface because it can generate an email on
its own for the notification of the alarm situation. (Once again, I'd
like to stick with the existing capabilities/functions of the system
parts to minimize rebuilding the functionality on another piece of

So we come back around to how to do what I asked in the first

Re: Serial Port Configuration
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To do what you want you would need some kind of program running on the
linux server that would detect the 2420 raising some kind of RTS line (
a behavior the people who make the camera could verify) or something,
then after detecting that it would need to lock the outgoing serial port
for transmit and pipe incomming charaters to and from the both serial
ports, possibly even capture and forward modem signal lines.

I still think that having the camera FTP a picture to the linux part
(which according to the docs is a built in function) and then having the
linux server run a script that does the emailing wouldn't be all that bad.

I suppose it comes down to what you think is easier, a program that
pipes two serial ports to each other while monitoring incomming
connections from either one. (Launch PPPD for connections coming from
the modem and launch the pipe connector program for connections going
out from the camera.

Also , you should be able to configure the linux server to dial out on
demand (if a request for an address not on its net is required, then it
automatically dials out). Not sure the procedure on that.
If that could be worked out then you could go back to etherent only,
then when the camera attempts to connect to the mail server, the linux
server will open the connection and then forward the packets on through.

I was just curious on the siteplayer part, if it is actually built into
your pic design or if it is just a separate ethernet to serial
conversion. Its capabilities could easily be put into the linux server side.

I guess if you are just trying hard to just shoestring together you are
OK using the siteplayer, but rethink the Camera opertion.
Then again, you might get lucky and find someone out there redirecting
serial services on demand.

My 6 cents now.

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