Am I Fomu ?

2019-05-20 - Louis-Philippe Véronneau

A few months ago at FOSDEM 2019 I got my hands on a pre-production version of the Fomu, a tiny open-hardware FPGA board that fits in your USB port. Building on the smash hit of the Tomu, the Fomu uses an ICE40UP5K FPGA instead of an ARM core.

I've never really been into hardware hacking, and much like hacking on the Linux kernel, messing with wires and soldering PCB boards always intimidated me. From my perspective, playing around with the Fomu looked like a nice way to test the water without drowning in it.

Since the bootloader wasn't written at the time, when I first got my Fomu hacker board there was no easy way to test if the board was working. Lucky for me, Giovanni Mascellani was around and flashed a test program on it using his Raspberry Pi and a bunch of hardware probes. I was really impressed by the feat, but it also seemed easy enough that I could do it.

My flashing jig

Back at home, I ordered a Raspberry Pi, bought some IC hooks and borrowed a soldering iron from my neighbour. It had been a while since I had soldered anything! Last time I did I was 14 years old and trying to save a buck making my own fencing mask and body cords...

My goal was to test foboot, the new DFU-compatible bootloader recently written by Sean Cross (xobs) to make flashing programs on the board more convenient. Replicating Giovanni's setup, I flashed the Fomu Raspbian image on my Pi and compiled the bootloader.

It took me a good 15 minutes to connect the IC hooks to the board, but I was successfully able to flash foboot on the Fomu! The board now greets me with:

[ 9751.556784] usb 8-2.4: new full-speed USB device number 31 using xhci_hcd
[ 9751.841038] usb 8-2.4: New USB device found, idVendor=1209, idProduct=70b1, bcdDevice= 1.01
[ 9751.841043] usb 8-2.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 9751.841046] usb 8-2.4: Product: Fomu Bootloader (0) v1.4-2-g1913767
[ 9751.841049] usb 8-2.4: Manufacturer: Kosagi

I don't have a use case for the Fomu yet, but I am sure by the time the production version ships out, people will have written interesting programs I can flash on it. In the meantime, it'll blink slowly in my laptop's USB port.