Some time ago I bought the following device:
https://retrogame300.com/products/retro-game-300
, to encourage myself to learn Rust by writing simple games for it. It's a mipsel device, so in theory it should be possible to compile Rust code for it. However, doing this is more complex that I anticipated.
This should also work on other devices using JZ4760 and RetroFW, such as the RS-97, Retro Arcade Mini and LDK.
See it in action here:
There aren't so many devices of this kind, and the ones I found sounded even harder for Rust. However, recently I found:
https://www.hardkernel.com/shop/odroid-go-advance/
, which could be a better option as it seems to use ARM which tends to be better supported.
The RG300 and a couple other devices tend to use buildroot to build small Linux distributions. The most popular seems to be RetroFW. However, soon I learnt that my device came with an old version of RetroFW which doesn't support niceties such as being able to do networking over USB to your computer.
So the first step I'd recommend is updating your system to the latest RetroFW version. To do so, you need to download an image from:
https://github.com/retrofw/retrofw.github.io/wiki/Install-Firmware
, in my case, my RG-300 had an IPS sticker and rg_300_v1.3 and 2019.6.3 printed in the circuit board under the battery, which points to the IPS version, so you can download the Type 5B version. I removed the internal microSD card, made a backup using dd of the original card and then used dd to overwrite the microSD card with the new firmaware. See the appendices for instructions about extracting the games from the original microSD card and setting them up on the updated RetroFW.
The microSD is apparently the only persistent storage of the RG300, so there's absolutely no risk to those operations. You can keep your original card and use a new one and swapping in the original microSD card will bring you back to the beginning.
(I'm now using exclusively the internal microSD card and not the external one. I prefer that, but it might be more convenient for you to use the external one)
With the latest RetroFW, if you connect your device to your computer using a USB cable and select Charger Mode, a private network will be set up between your computer and the device. You can use telnet and FTP to connect to the device using 169.254.1.1 as the address.
RetroFW uses some kind of fork of buildroot which comes with Rust 1.23.0. Besides being old, this is also problematic as recent versions of Rust updated the mips targets to generate mips32r2 instructions:
I opened a bug to see if they restore support:
In the meantime. I created some patches to fix this working. I made them on top of master, but they apply well on top of the 2020.02.x branch, which should be more stable. They are in this repo as 00*. 0001-0009 are some patches that @glebm showed me that update Rust to 1.40.0. 0010 is an ugly buildroot hack that forces buildroot to build Rust for the mipsel-unknown-linux-uclibc target; buildroot doesn't want to build Rust on uclibc (it's a tier 3 target for Rust, so it's not built nor tested automatically). This is ugly and borks building any other target. 0011 adds a patch on top of Rust to buildroot which disables the generation of mips32r2 instructions.
To build, apply those patches and copy buildroot-config in this repo as .config to the root of the buildroot repo. Then build according to buildroot's instructions.
You can build this repo by altering your PATH with:
$ export PATH=/path/to/buildroot/output/host/bin/:$PATH
and then running:
$ cargo build --target mipsel-unknown-linux-uclibc --release
To run this software, I use lftp to copy the binary over:
$ lftp 169.254.1.1
> cd /home/retrofw
> put target/mipsel-unknown-linux-uclibc/release/retrofw2-rust
Once it is copied, you can enable debug logs by activating the "Output logs" option in Settings. Then use apps / Explorer to locate retrofw2-rust in /home/retrofw and execute it. Use the Select button to quit. Start will switch between modes:
- Draw some color bars
- Show which buttons are being pressed
- Show a one-pixel alternating checkerboard pattern (useful to verify screen resolution)
- Play periodic sine waves
You can see the output by going to the settings screen and using the new Log Viewer application.
Note that you can also run the program natively on your workstation for development/prototyping/debugging. If your desktop uses pulseaudio, use padsp to run the program.
RetroFW seems to cap the framerate to 60fps, but on my laptop it seems to be unthrottled. I wasn't able to write generic code that will throttle adequately all environments to 60fps, so in the asteroids example I do conditional compilation of the throttling code.
My RG300 came with an SD full of software; after overwriting your internal card, you will have an "empty" RetroFW installation. After doing this, I grabbed the starter pack zips, unzipped the OPKs, copied them to the internal SD card and did the "update OPK links thing". This will install a similar set of emulators (and some applications) to the one that originally came with the device.
After that, I extracted the ROMs folder from my original microSD backup (you can use losetup -P to create a loop device per partition in the SD card, the third one contains the games) and copied them too to the internal microSD card. I think the menu integration is slightly worse now, but they seem to work.
@glebm, @pingflood, @jbanes on #developer-talk on the RetroFW discord, which helped a noob in these affairs :)