Johnny Castaway Native Live CD
Once again, I am reminded of how much the past influences our future, and the choices we make. In my case, it’s a twisty tale that starts simply enough, but ends with Johnny Castaway running natively from a ramdisk on systems with as little as 64mb. Interested? Read on. Want to download it for yourself right now? Skip to the end!
And here’s a nice video from VirtualBox :)
This story starts with wonderful news, one of the talented developers working to re-implement Johnny Castaway has done so in a languge I quite enjoy (ansi c), and quite successfully. When I stumbled upon the newest code for ‘Johnny Reborn’ (https://github.com/jno6809/jc_reborn), written by the talented Jérémie GUILLAUME, a few things stood out to me:
- This is a fully baked re-implementation of Johnny Castaway
- It’s currently working
- It’s written in ansi C-99 and SDL 2
- The above code is quite clean, enjoyably so
- It is criminally under-exposed for how good it is (2 watchers, 8 stars, 1 fork (mine))
There have been a few re-implementations of Johnny over the years, but I’ve always chosen to emulate Johnny using Dosbox or Wine. Why? These re-implementations used resource-intensive high-level languages and libraries. They wouldn’t run particularly well on a 25 year old PC! I know that’s not a use case most folks still have, but it’s of special interest to me :) So when I dug into this re-implementation, I knew it was something special. Clean, straightforward code. Runs in a few megs of ram, no noticeable memory leaks, low CPU usage even on ancient (486) class machines. Immediately made me smile in a way I hadn’t in some time.
So, I did what anyone in my situation would do, I set out to cross-compile a 32-bit version of Johnny I could boot live on low-end systems (edit: tested working with as low as 64mb ram!). [download that binary, or a live linux ISO] (https://github.com/huntergdavis/jc_reborn/ )
This worked well enough, but unfortunately at least one of the laptops I was booting it on doesn’t support Xvesa/Xorg. Framebuffer was an option through, so I set about to boot to console and execute in console-FB.
Bummer, SDL 2.0 doesn’t support console framebuffer any longer. I was facing a large number of hoops to try and layer in xfcb-dev onto tinycore and boot on my particular craptop, and I realized something.
Lightbulb moment! Why not just re-write the graphics layer of johnny-reborn in SDL 1.2?. That does support framebuffer backends, and it’s fairly similar to SDL 2! So that’s just what I did, a quick SDL 2.0->1.2 backport for Johnny. Source here
Second Lightbulb moment! SDL 1.2 doesn’t just support framebuffer backends. It’s fifteen+ years old at this point, and it supports some popular systems of that era. One in particular caught my eye - the Sega Dreamcast. Why?
- I love the Sega Dreamcast. So Much.
- It supports 640x480 natively, default resolution for JC_reborn, no need to write a scaler
- You can craft an ISO with the right audio track and boot on many stock Dreamcast units.
- Emulators are plentiful and run on all kinds of hardware (Android, game devices, etc)
So, I set about my plan.
- Install the kallistos libraries and cross-compile environment
- compile kallistos-ports (including sdl1.2)
- update the init and file i/o for johnny to dreamcast flavor
- compile elf executable, convert to bin, scramble bin, convert to 1ST_RUN.BIN
- assemble IP.BIN, assemble iso, convert to CDI
- test on emulator
Out of scope for this initial release
- Updating dc-specific features (i.e. VMU support)
- Testing on actual hardware (I’ll need to buy one that supports reading CD-R disks, pre-2000 manufacture date)
How did that go? Well, I’ve found out something that many Dreamcast developers know very well, it’s very hard to debug i/o in an emulator! Much easier on actual hardware. So, pending my next purchase of a Dreamcast, those preliminary commits are available for anyone looking to try. here
Anyway, back to the live CD, I was looking to boot with a dynamically linked SDL 1.2 with console-framebuffer support (SDL 1.2 only allowed static linking if you buy a pro license, boo!). There were still a couple of hoops to jump through though:
- Mouse support! Not likely. Export SDL_NOMOUSE=1 (you’ll see this in /home/tc/.profile on the ISO)
- pass ‘‘text’ parameter to grub on boot (don’t attempt to startx)
- set the desired vga output for FBconsole. This gets picked up from the vga=XXX grub boot parameter (640x480x32 is vga=786)
- auto-start johnny directly. For the live CD I just add this to /home/tc/.profile and busybox will pick it up on autologin.
And that’s about it! You can download a live ISO that’ll boot to ram from any supported medium (17 megabytes or above, sorry floppy friends!) here A giant thanks to Jérémie GUILLAUME for re-implementing Johnny in a clean, portable format that really made my day!!
Here’s a video of that very ISO booting from a burnt-CD (remember those!) on my beloved 2001 era Thinkpad (256mb RAM)