During an upgrade from pfsense 2.1.5 (FreeBSD 8) to pfsense 2.2 (FreeBSD 10), my AMD APU router became unresponsive using tools such as ping and ssh. It required connecting via serial console. Here’s a quick overview.

Model number of the board: PCEnginges APU1C4 T40E
USB to male serial: TRENDnet USB to RS-232 DB9 Serial Converter
Null model cable: DB9 RS232 Serial Null Modem Cable F/F (SCNM9FF)
Build reference: Unpacking and Assembling PC Engines APU

I have an older Lenovo Thinkpad T400 acting as a server running CentOS 7 that provides lightweight services such as DHCP, DNS, and iPXE to my LAN. To gain access to the router’s console, I plugged in the serial converter above to the Thinkpad and attached it to the null-modem cable that was hooked up to the router.

I verified on the laptop that everything was detected via dmesg | tail -10 and ls -l /dev/ttyUSB?, which showed the following:

$ dmesg | tail -25
[4643071.873119] usb 6-2: new full-speed USB device number 2 using uhci_hcd
[4643072.019109] usb 6-2: New USB device found, idVendor=067b, idProduct=2303
[4643072.019119] usb 6-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[4643072.019126] usb 6-2: Product: USB-Serial Controller D
[4643072.019131] usb 6-2: Manufacturer: Prolific Technology Inc.
[4643072.128738] usbcore: registered new interface driver pl2303
[4643072.128766] usbserial: USB Serial support registered for pl2303
[4643072.128785] pl2303 6-2:1.0: pl2303 converter detected
[4643072.140519] usb 6-2: pl2303 converter now attached to ttyUSB0

$ ls -l /dev/ttyUSB?
crw-rw----. 1 root dialout 188, 0 Jan 24 17:59 /dev/ttyUSB0


To connect to the console, I used the following command:

screen /dev/ttyUSB0 115200

From there I was able to troubleshoot and debug as necessary on the pfsense shell.