This is a project I worked on for university. It is supposed to be about bringing the functional programming language "elm" to the world of microcontrollers. Elm is throught to be a language for the web and thus compiles to JavaScript.
Here are some facts:
- There is support for NodeJS in elm, but since there is no NodeJS on embedded systems, I had to disect the generated file manually.
- The generated Javascript-file is about 5000 lines long. I've tried multiple embedded JS-projects (Espruino, Duktape, JerryScript) and none could handle that large file on an STM32F4 with 192k RAM.
- I've compiled my attempt with Duktape for Linux to run on my desktop-computer - worked fine.
- Running the closure-compiler on the generated file to reduce it's size didn't help either.
In conclusion: I didn't get elm to run on an embedded system. A RaspberryPi would have worked, but at that point I kinda gave up.
There are some other promising projects which allow to run some JS-Code via NodeJS on a PC and only send small commands to a connected Arduino, for example. One of those projects is "Johnny-Five", and I had it running quite fast. From the idea to a blinking LED using NodeJS and Elm in under half an hour!
But a blinking LED would be too simple, right?
Entering: The Gameboy Advance!
I played around with the GBAs multiboot-capability (that is: upload a small rom using the Link-Cable) before, but couldn't get it to work. I still had my modified GBA laying around... (which I had no cables for, so it looks kind of demolished now since I had to solder some directly to the board and broke the casing while doing so)
Since the Gameboy uses the simple SPI-Protocol for communication, which is a widely adopted industry standard, and the Arduino has a library for that, I thought: "Why not? That would be fun!".
A small (kinda-working) prototype in C later: Time to port this thing to johnny-five and elm!
... too bad, there is no SPI-Support in Johnny-five.
My first attempt had the Arduino just being a proxy, getting the SPI-commands from the serial-connection and sending the contents straight to the Gameboy. Couldn't get that to work, unfortunately.
I ended up coding the whole protocol in C on the arduino, using an extremly simple custom serial protocol to talk to NodeJS and Elm on the PC-side of things.
So, to upload a ROM to the Gameboy, one would have Elm send the ROM-Data over a serial-connection to the arduino, which then talks to the gameboy, encrypts the data and sends it further down the line.
The Elm-Program basically resembles a state machine and uses ports to talk to NodeJS, which I tried to use as little as possible.
I guess writing the PC-side in pure JS, rather than Elm would have made the code a lot shorter and easier to read. I'm still learning Elm though, so maybe there is some cool feature which would get rid of like 80% of the complexity.
My main issues with the elm-version is the obfuscated control-flow. But I probably just suck at writing Elm :)
There isn't really going on much in the Elm-program, which makes use of the features that make functional programming shine. I wish I had time to move the whole protocoll over to Elm, but with the like 4 failed attempts on getting Elm to run on a microcontroller, time was running out.
If someone really wants to try this: (makes little sense without the arduino hooked up to the gameboy)
mkdir node_modules
elm-make elm-flash.elm --output node_modules/elm-flash.jsnode flash.js /dev/ttyACM0 gbahello_mb.gba