Connect to a modified router

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Revision as of 16:35, 21 March 2007 by Brylow (Talk | contribs)

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Contents

Summary

This will explain how to connect to the serial ports on a modified LinkSys WRT54G using serial communication software such as the open source Kermit.

Before Starting

Expose a serial port on the router

You must have successfully modified a LinkSys WRT54G to expose at least its first serial port in such a way that you can connect it to another machine with serial communications software. If you have not done so yet, please see HOWTO:Modify the Linksys hardware

Acquire serial communication software

A solid open source suite of communication software known as Kermit has served us well as a method of communicating with the WRT54G. C-Kermit, the UNIX compatible implementation, is available for download at their website [1]. Alternatively, if you are building multiple backends to be made available as a pool, our suite of XINU Console Tools includes a basic serial console utility called tty-connect.

Steps to Connect to the Router

Task One: Power up the Router

Yes, that means plug it in.

Task Two: Connect Serial (& Optionally Network) Cable(s)

Ensure that the connection is going from UART0 (the first serial port--you did label them didn't you?) as this is where the console will be running. If you are connecting a standard PC serial port (a DTE) to your router, use a straight serial cable. Other arrangements may require a Null Modem; check your transmit/receive line polarities to be sure.

Also, because the goal is to upload custom code to the router, it would be a good idea to connect the router to your network by wiring it up via one of the numbered LAN ports on the back of the router (NOT the Internet/WAN port).

Task Three: Configure your Serial Communication Software

The connection used by the router's serial port is fairly standard: 115200bps, with 8 data bits, no parity bit, and 1 stop bit, or 8N1.

In our setup, once running Kermit on the external machine, we connected by typing in:

set line /dev/tty000      to select the serial device that is connected to the router*.
set serial 8n1      which is not really necessary since this is default.
set speed 115200      as given to us in the router specifications.

(* - Your device is probably different. Check your O/S documentation to figure out the name of your computer's relevant serial port.)

Task Four: Connect to the OpenWRT Console

In Kermit, after the configuration commands have been entered, it was as easy as typing connect. Once connected, press Enter to get a console from OpenWRT. This should function just about identically to the ssh console, and if it works correctly, it means that the serial port has been correctly installed.

Task Five: Access the Common Firmware Environment CLI

This will be filled in, but here's the basics:

  • Make sure boot_wait is on (this should be added to the Install OpenWRT HOWTO)
  • Reboot the router (reboot or power cycle).
  • Hit CTRL+C on your serial console.
  • You're in.

What to do next?

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