My Homemade LOM

In one of the final classes of my CS master’s program, Embedded Computing, we were required to complete a semester project of our choosing involving embedded systems. Like in previous semester projects, I wanted to do something that I would actually be able to use after the class ended.

This time around I chose to build a lights-out manager for my Sun Ultra 24 server (which this blog is hosted on). With a LOM I can control the system’s power and access its serial console so I will be able to perform OS updates remotely, among other things.

Since I already owned one and I didn’t want to spend a lot of money, I chose to develop the project on top of the Arduino platform. I like the size of the Arduino, and the availability of different shields to minimize soldering. It’s also able to be powered by USB, which is perfect because the Ultra 24 has an internal USB port that always supplies power.

To make things a little more challenging for myself (because the Arduino is pretty easy on its own), I chose to implement a hardware UART to communicate with the Ultra 24’s serial port. Specifically, I chose to use the Maxim MAX3110E SPI UART and RS-232 transceiver. Great little chip.

For communication with the outside world, I bought an Ethernet shield from Freetronics. It’s compatible with the official Arduino Ethernet shield, but includes a fix to allow the network module to work with other SPI devices (such as my UART) on the same bus. I started to implement the network UI using Telnet, but after realizing I would have to translate the serial console data from VT100 to NVT, I switched to Rlogin, which is like Telnet, but assumes like-to-like terminal types.

Lastly, for controling the system’s power, I figured out how to tap into the Ultra 24’s power LED and switch. Using the LED, I can check whether the system is on or off, and using the switch circuit and a transistor, I can power the system on and off. I managed to do this without affecting the operation of the front panel buttons/LEDs.

I’ll spare you all of the implementation details (if you’re interested, you can read my report). Suffice it to say, the thing works as well as I could have imagined. Here is a screenshot of me using the serial console on my workstation:

From my research, the serial and power motherboard headers are the same on most modern Intel systems, so this LOM should work on more than just an Ultra 24. If you want to build one of your own, my code is available on GitHub and the hardware schematic is in the report I linked to above.

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