Connect to a modified router

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

There is a freely available software package for serial communication on almost every major platform. A solid open source suite of communication software known as Kermit has served us well as a method of communicating with the WRT54GL. C-Kermit is the UNIX compatible implementation, and a Windows version, Kermit 95, is available as well.

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: 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 Two: 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. Set your software to connect using these settings.

Task Three: Power up the Router

Yes, that means plug it in.

With serial communications software listening, you should see something like the following output:

CFE version 1.0.37 for BCM947XX (32bit,SP,LE)
Build Date: Mon Nov 14 18:06:25 CST 2005 (root@localhost.localdomain)
Copyright (C) 2000,2001,2002,2003 Broadcom Corporation.

Initializing Arena
Initializing Devices.

No DPN
et0: Broadcom BCM47xx 10/100 Mbps Ethernet Controller 3.90.37.0
CPU type 0x29008: 200MHz
Total memory: 16384 KBytes

Total memory used by CFE:  0x80300000 - 0x803A39C0 (670144)
Initialized Data:          0x803398D0 - 0x8033BFE0 (10000)
BSS Area:                  0x8033BFE0 - 0x8033D9C0 (6624)
Local Heap:                0x8033D9C0 - 0x803A19C0 (409600)
Stack Area:                0x803A19C0 - 0x803A39C0 (8192)
Text (code) segment:       0x80300000 - 0x803398D0 (235728)
Boot area (physical):      0x003A4000 - 0x003E4000
Relocation Factor:         I:00000000 - D:00000000

Boot version: v3.7
The boot is CFE

mac_init(): Find mac [00:18:39:6F:78:15] in location 0
Nothing...

eou_key_init(): Find key pair in location 0
The eou device id is same
The eou public key is same
The eou private key is same
Device eth0:  hwaddr 00-18-39-6F-78-15, ipaddr 192.168.1.1, mask 255.255.255.0
        gateway not set, nameserver not set
Loader:raw Filesys:raw Dev:flash0.os File: Options:(null)
Loading: ...... 1601536 bytes read
Entry at 0x80001000
Closing network.
Starting program at 0x80001000
CPU revision is: 00029008
Primary instruction cache 16kb, linesize 16 bytes (2 ways)
Primary data cache 8kb, linesize 16 bytes (2 ways)
Linux version 2.4.20 (root@localhost.localdomain) (gcc version 3.2.3 with Broadcom modifications)
...
(snip)
...
Hit enter to continue...

Pressing enter will give you a root shell:

BusyBox v0.60.0 (2005.11.14-09:45+0000) Built-in shell (msh)
Enter 'help' for a list of built-in commands.

#

Task Four: Access the Common Firmware Environment CLI

If you reboot the router while holding CTRL+C on the serial console, you will get a CFE prompt.

CFE version 1.0.37 for BCM947XX (32bit,SP,LE)
Build Date: Mon Nov 14 18:06:25 CST 2005 (root@localhost.localdomain)
Copyright (C) 2000,2001,2002,2003 Broadcom Corporation.

Initializing Arena
Initializing Devices.

No DPN
et0: Broadcom BCM47xx 10/100 Mbps Ethernet Controller 3.90.37.0
CPU type 0x29008: 200MHz
Total memory: 16384 KBytes

Total memory used by CFE:  0x80300000 - 0x803A39C0 (670144)
Initialized Data:          0x803398D0 - 0x8033BFE0 (10000)
BSS Area:                  0x8033BFE0 - 0x8033D9C0 (6624)
Local Heap:                0x8033D9C0 - 0x803A19C0 (409600)
Stack Area:                0x803A19C0 - 0x803A39C0 (8192)
Text (code) segment:       0x80300000 - 0x803398D0 (235728)
Boot area (physical):      0x003A4000 - 0x003E4000
Relocation Factor:         I:00000000 - D:00000000

Boot version: v3.7
The boot is CFE

mac_init(): Find mac [00:18:39:6F:78:15] in location 0
Nothing...

eou_key_init(): Find key pair in location 0
The eou device id is same
The eou public key is same
The eou private key is same
Device eth0:  hwaddr 00-18-39-6F-78-15, ipaddr 192.168.1.1, mask 255.255.255.0
        gateway not set, nameserver not set
Automatic startup canceled via Ctrl-C
CFE> ^C
CFE> ^C
CFE>

See the CFE page for more information about using this prompt.

What to do next?

Now that you have successfully modified and connected to your router, you are ready to Build and Deploy XINU.