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Building Fuxiz for the MSP430FR5969


The MSP430FR5969 is a very small embedded microcontroller made by Texas Instruments. See here for more information:

You can run Fuzix on it, if you connect up an SD card reader to the appropriate pins. The easiest way to do this is to get the Launchpad evaluation board:

...and then get the SD card Boosterpack from here:

...and plug it in. The Fuzix port's console is, by default, on the right pins so that the Launchpad's USB serial emulation will Just Work. Power up the board, plug in the SD card, start your serial terminal, hit the reset button, and you should get a shell.

What's supported

The MSP430FR5969 does not have a lot of RAM. Fuzix will run a single 23kB user process at a time, and uses swap onto the SD card to allow you to run other programs. Timeslicing is not supported. You can run up to four processes (although it'd be trivial to add more).

There's a full filesystem on the SD card with a tonne of software. The Bourne shell runs, most basic commands are present, and you can program in sh or forth. It's actually surprisingly snappy and pleasant to work with.

Even the games work.

Required software

This has only really been tried on Debian Linux, on an amd64 machine. If you're on something else... sorry. It shouldn't be too hard to build on any Unixoids.

You will need:


Once you've got all that set up, you should just be able to do:

make -j PLATFORM=msp430fr5969

...and it'll all happen. You'll end up with three files; the kernel image, called kernel-msp430fr5969.elf, a corresponding map file which you can ignore, and the file system image, called filesystem-msp430fr5969.img.

Now you're ready to install it!


First, prepare the SD card. Create an MSDOS partition table, and add two partitions at least 10MB in size. The partition type or active flag is irrelevant.

The first one is the file system; dd the filesystem image onto it. The second is the swap partition, which doesn't need preparation.

Insert the SD card into the device and connect it up. Start your serial terminal.

Now flash the kernel onto the device with:

mspdebug tilib "prog kernel-msp430fr5969.elf"

You'll see the kernel image being written into the device's persistent storage, and then it'll reset, and (with luck) you'll get a shell.


It's a bit fragile. Some applications crash it, such as wumpus. I don't know why; there should be enough RAM.

There's something wrong with the SD card interface, and it's rather unreliable. Once the SD card is detected correctly, it seems to be fine. I think it's not being initialised correctly.

It's really, really short of RAM. Ideally the whole kernel needs to be rejigged so that the kernel is built in large mode, which means a lot of it can live in high memory, which isn't accessible to user processes (which run in small mode). However, Fuzix currently assumes that sizeof(int) == sizeof(void*), so that may not work. Also, large mode instructions on the MSP430 are way bigger than small mode ones, and the extra overhead may not be worth it. If only mspgcc supported mixed mode, with 20-bit code pointers and 16-bit data pointers...

David Given