Monthly Archives: August 2016

XGS Lives

Believe it or not, XGS is now 20 years old! The project was started way back in 1996, when my fastest PC was still a 66 MHz Pentium. Sadly, for various reasons, development pretty much stalled in 1997. I briefly started tinkering with it again in 2002, but I got busy, and nothing came of it. The last released version is still from 1997…but that’s about to change.

Lately I’ve found myself in need of a good personal project to sink my teeth into, and so I’ve circled back around to XGS.  I have two goals in mind for the future of XGS:

  1. Finishing what I started 20 years ago.  I want to find and fix the bugs that keep some high-profile software from running (hi Diversi-Tune!), improve the emulation (3200-color support anyone?), and apply some spit and polish in the form of an actual GUI.
  2. Create a version of XGS that is geared towards running on a Raspberry Pi to create a teeny-tiny Apple IIGS. Part of this project would involve some actual hardware hacking to create interfaces to authentic Apple hardware. I for sure would like to implement ADB, so that a real IIGS keyboard and mouse can be used. I’m also considering trying to drive an actual 3.5″ 800k drive, which would be great if there’s anyone out there with some stuff on old IIGS disks.

With those goals mind, the first decision I’ve made is that I’m no longer going to go out of my way to make the code portable beyond Linux. I certainly won’t object if anyone wants to resurrect any of the other ports, and I will try to not make things hard on anyone who wants to do so, but if I can do something cleaner and/or easier by targeting just Linux that is the way I will go. Case in point: the current code base is using the Linux timerfd interface for timing, because it just works way better for me than straight POSIX timers (I did try them!)

Next, I’ve mostly finished up some work I started back in 2002 to replace all the individual video and audio drivers with a single set. Currently that’s SDL for video and PulseAudio for audio. I wanted to use SDL for both, but I so far I’ve been unable to get SDL audio that doesn’t have lots of skips and crackles. SDL does have the benefit of being multi-platform so at least here I hopefully made things easier for any would-be port maintainers.

I’m also looking at ways to simplify the code by removing some roundabout ways of doing things that were originally implemented to make the emulator actually usable on 1996-vintage PCs. The new low-end for acceptable performance is going to be a Raspberry Pi 2.

And finally, I’m considering changing the code base from C to C++ and implementing the various hardware chips as their own classes. This isn’t fundamentally different than what is there now, but the resulting code will be much cleaner, and the interfaces between the various emulated hardware bits will be well-defined. It will also aid in my long-term Raspberry Pi goals, because I’m going to need to be able to plug in different bits cleanly (e.g remove ADB emulation and replace with an interface to my yet-to-be-designed ADB hardware).

I’m really excited about all this, and I’m hoping to start pushing out some new development snapshots this month. Stay tuned!