You need to enact a secret incantation to unlock the u-boot console on the WRP400.

• Solder on a SerialPort.
• Boot the device to userspace as normal.
• Access the following secret URL to unlock the console:

    http://192.168.15.1/CgiCommand.htm?command=TftpOn&user=admin&pass=admin
    (replace 192.168.15.1 with the IP address of your wrp400, and use the correct admin password if you've changed it from the default)

• Reboot the device with a console attached to the SerialPort.
• Note that the u-boot console is now unlocked and you can hit Ctrl-C on the serial console during the 1 second u-boot autoboot delay.

You now have a normal u-boot console.

• Access the following secret URL to lock the console:

    http://192.168.15.1/CgiCommand.htm?command=TftpOn&user=admin&pass=admin
    (replace 192.168.15.1 with the IP address of your wrp400, and use the correct admin password if you've changed it from the default)

Note that the reset button has no effect on the console_state variable.