Add a Serial port to the MIPS Linkstation
The console is the text output device for system administration messages. These messages come from the kernel, from the init system and from the system logger. On modern small computers the console is usually the computer's attached monitor and keyboard. The LinkStation, however, doesn't have monitor output; instead, it uses a serial connection for console output. Not only does the serial console provide valuable debugging output, it also allows root access!
Most of the information on this page was originally only speculation, based on roughly deciphered information from a Japanes web page. At the end of 2006 the community bought a bricked LS2 and handed it over to Tampakuro aka Kuroguy for trying out various hardware modifications. While at it, kuroguy also verified the procedure for installing a serial console interface. This page has been updated with the information and photos he provided in Hardware Hacks for the LS2.
- (1)Electronic-grade soldering iron (think really small)
- (1) 0.015", 1 oz solder
- (1) 0.1” series PCB header plug, 4-pin
- (1) Serial converter (or build your own - see step 4)
Access the Board
- Disassemble the LinkStation.
- Remove the main circuit board by removing the 4 mounting screws:
- Place the circuit board on a static-free work area:
Attach Header to the Board
- The console header needs to be attached to the J1 pad
- Remove the preexisting solder from J1
Enable Full Serial Tx/Rx
To enable write support across the serial port, simply bridge R186.
The Serial Converter
The serial port signals from the processor are only 3.3V. For proper RS-232 12V signaling, an RS-232 level shifter needs to be added. These are very common in PDA serial cables also, but can be purchased from SuperDroid Robots (#MCU-026-172) or CompSys (#A232DBH3v).
- As an alternative you can make the level shifter cable yourself:
- Warning: The following image depicts 0.1mF (m = milli) capacitors, while in reality 0.1µF (µ = micro), alias 100nF (n = nano) capacitors are needed for the original MAX3232! The list of parts is correct.
- Components can be found at e.g. Digikey
- If you want to build your own serial converter, you will need the following parts:
- (5) 0.1 µF tantalum capacitors
- (1) MAX3232CPE IC (Maxim), 3V type, 16 pin DIL
- (1) RS232 male socket
- (1) Some perf board (about 1" x 1")
- (1) Wire
You can etch a circuit board which makes building the interface and installing the interface really easy. Instructions are Here.
This should be attached as close as possible to the board. The signals are very weak and wires as short as 2" (5 cm) have been reported to cause data loss across the serial port.
Enabling the Serial Console
As the LS2 only has a single serial port which is used by the housekeeping microcontroller, it is necessary to enable the serial console. This is done by jumpering the pins of J2 and disabling the watchdog timer on startup (by pressing the red button and powereing it up). It is easiest to install J2 on the back of the board as it will be accessible by removing the cover and not the board from the chassis I used a red jumper so it can be easily located. Another option to removing the cover is to drill a 3/8" hole in the case directly above J2 and make a handle for your jumper from a piece of tape.
Using the Serial Console
Of course you need a serial cable to connect to the serial port. Depending on how you wired the plug on the LS, you will need a null modem, too, or a null modem cable.
- You may access the serial console using Windows HyperTerminal (included with Windows) or TeraTerm Pro terminal emulator.
- classic Unix
- If you have a classic Unix you should either have tip(1) or cu(1) (or both). They are suitable to set up a serial connection. Linux typically doesn't have these.
- If you are on Linux, consider the trusted and tried miniterm terminal emulator. 'minicom' also works nicely.
- If you are the proud owner of a real oldschool terminal, this is your chance to make use of the old dust catcher :-)
Serial Port Settings