About a week and half ago I became the owner of Raspberry Pi 400, a small computer built around a Raspberry Pi 4. The kit I purchased came with a USB-C power adapter and a basic USB mouse; all I needed to supply was a monitor.
Naturally, the first thing I did after setting it up was get XGS running on it:
This was not quite as simple compiling XGS and running it, so let’s go over what changed, why it changed, and how to build XGS on the Pi after the changes.
Open GL Support on the Raspberry Pi
On older Pi models (1, 2, 3, and the Zero) the OpenGL support was provided through a proprietary firmware blob, and exposed through a set of custom GL libraries in /opt/vc/lib. Since 2017 XGS supported use of these libraries by specifying -DBCMHOST=true when running cmake.
As of the Pi 4 (and, by extension, the Pi 400) this proprietary firmware driver is no longer supported. Instead, there are now open source drivers supporting the Pi 3 and 4. They are fully integrated into Mesa now, so it is no longer necessary to link against proprietary libraries.
As a result of these changes I have decided to remove the BCMHOST option in XGS. Instead, XGS relies on SDL to pick the right driver; this will be KMSDRM when running from the console, or X11 when running from the desktop.
Note that this change has probably broken support for the Pi 1 or 2. Those models are sufficiently outdated now that I don’t feel the need to continue supporting them.
As of this writing Raspberry Pi OS does not ship a version of SDL with the KMSDRM driver enabled. So, before building XGS, you’ll need to build and install your own build of SDL. Fortunately this is very easy:
sudo apt-get remove -y --force-yes libsdl2-dev
sudo apt-get install libgbm-dev libdrm-dev
tar -xzvf SDL2-2.0.12.tar.gz
./configure --host=arm-raspberry-linux-gnueabihf \
sudo make install
You should also run raspi-config, navigate to Advanced Options -> GL Driver, and make sure you have the KMS driver selected. You’ll need to reboot after making this change.
With SDL built and the KMS driver enabled you can now build XGS:
The resulting binary can be run from the desktop or direct from the console. It will open in a window when run from the desktop, and full-screen when run from the console.
The only problem I have noticed is that the video is a bit choppy when running from the console. It’s most noticeable when watching the sliding apple on the “Check startup device” screen. It does not happen when running from the desktop, so it is somehow related to the KMSDRM driver.
Raspberry Pi & the Future of XGS
XGS has certainly had a fragmented development history. I originally started it in 1996, but by 1997 development had already stalled. Five years later, in 2002, I briefly resumed work on it, but I also started a small business around that time and XGS ended up on a (virtual) shelf for nearly 15 years.
Fast forward to 2016, when I got the XGS itch again. I rewrote the code in C++ to make it easier to understand, removed non-SDL graphics support, and added a basic GUI.
By 2017 I had moved away from the project again despite making good progress. I briefly considered creating a retro emulated GS based around the Raspberry Pi (think of the C64 Mini) but that project never really got off of the ground, and by that point I was already spending the bulk of my time on other projects.
And so here we are in 2020. I’m currently between hardware projects (well sort of; more on that in another post) and I’m feeling the need to spend at least some of my free time on a software project. So, I am jumping back into XGS, with the intent of improving the Raspberry Pi support. My first task will be to create an ARM-optimized version of the M65816 emulation core. I’ve been wanting to learn ARM assembly, and this will be a great way to do that.
Traditionally I’ve never been one to put a great deal of effort into Halloween. This year, however, I decided I wanted to go as Rick from “Rick & Morty”, and i wanted the centerpiece of my costume to be a fully-functional portal gun prop (it could be argued that the costume was just an excuse to build the gun). So, I set out to build the Rickest portal gun of them all: a fully 3-D printed replica containing a micro projector powered by a Raspberry Pi that could project fully animated portals with sound.
The first thing I did was some research. I immediately came across this project, which is very impressive, but it was rather limited due to the use of a projector with an SD card slot. He can’t control the projector without it popping up its OSD, so the animation is always looping, and he uses some clever hacks to only show it when he wants it to be visible. I knew I could do better.
My next step was to get an idea of the dimensions for the gun I was going to build. After checking out dozens of other projects on the web I settled on having the main body of the gun be roughly 6″ long, 4″ wide, and 2″ high. This made the gun look aesthetically pleasing, and would just barely fit inside my printer’s build volume.
Choosing the Hardware
With the dimensions chosen and some rough sketches made I set out to select the parts to go inside the gun. A Raspberry Pi Zero was the obvious choice for the controller, since it’s cheap, tiny, and has enough horsepower to run the animation I wanted to display. I also settled on a Quad Alphanumeric Display from Adafruit for displaying the selected destination universe. The display is controlled via I2C which is perfect for interfacing to the Pi. It is available in red (and several other colors), but red was out of stock at the time so i went with the white version and a red plastic filter.
For the projector I settled on an APEMAN Mini Projector from Amazon. It has a decent output brightness, built-in speakers, and a USB output that can power external devices from its internal battery, meaning I wouldn’t need to wedge in another power source for the Pi and LEDs. It also happens to be 4″ x 4″ square which perfectly fit with the dimensions I had decided on for the body of the gun. At $200 it was by far the most expensive piece of this project!
Finally, I picked up a simple rotary encoder for the control knob, and some DIY HDMI cable parts from Adafruit to build a short, flexible cable for connecting the Pi and the projector.
With my parts acquired I began building a prototype. I framed out a basic version of the body with cardboard so that I could test fit everything. I then hooked up everything the way it would be connected in the final product and did some testing to make sure everything played nice together.On the left is the projector, connected via an HDMI ribbon cable and a home built USB power cable to the Pi, which is in turn wired to the display and the rotary encoder. Near the top center you can see my cardboard prototype for the gun body.
With the hardware proof of concept built I set out to design the software. My plan was to write some code that talked OpenGL directly to the GPU on the Pi, bypassing the need to run an X server. I was hoping to write a fancy shader that would actually generate the portal directly, but settled for a simpler setup with a static image and a modified version of a swirl filter shader that would rotate the static image. It also scales the image to create the open & close effects. This actually took surprisingly little time to create; I went from no code to a working prototype in a couple of hours.
Here’s the image that is used for the portal:
Next I had to add sound effects. The projector has two internal speakers so all I had to do was redirect the Pi’s audio output over the HDMI. The problem came when I tried to find some good sound samples to use. I found a decent “portal opening” sound, but was unable to find a matching “portal closing” sound. In the end I used Audacity to copy a portion of the opening sound and reverse it.
Last up was the alphanumeric display. This was simply a matter of using Adafruit’s sample code for the Arduino and converting it to run on the Pi. I had originally programmed it to just count sequentially as the knob was turned, but I realized that for a “real” portal gun that would be a horrible user experience, so I implemented a “favorites list” of known destinations from the show and had the knob scroll between those.
Once the software was finished I created a “pg” user on the Pi and set it to auto-login and run the app as soon as the Pi boots.
In the end I spent the better part of a week writing and tweaking the software. It would have gone faster if I’d had a cross-compile environment set up, but I don’t, so I had to do all my compiles on the Pi. It is NOT a fast process!
Building the Gun Body
By far the most time-consuming part of the project was designing and printing the gun body. I pushed my FreeCAD skills to their limits designing all the pieces, and ended up going through several iterations before settling on a final design that worked.
When I started out designing the body I had planned to print it in four pieces. The main (rectangular) part of the body would be printed as a box and a lid, with a black front panel held in place by slots, and the handle would be separate and attached to the back via screws. This turned out to be a bad idea for a couple of reasons:
1, My original design for the box (minus lid) was going to be an 11+ hour print. Every time I wanted to tweak anything would mean yet another 11 hours, not to mention all the wasted plastic.
2. I kept running into problems when trying to design complicated designs in FreeCAD; I would want to go back and change something and it would end up destroying my entire design. This is probably just a skill-level problem on my part, but in the end it was faster for me to design multiple smaller pieces instead of a few large ones.
So after a lot of thought I decided to print the top, bottom, front, and side pieces individually and then connect them with M1.5 screws and a little glue for added strength. Here’s my first prototype for the bottom panel:
The four square posts are for holding the projector, which needs to be centered vertically in the gun so that the projector output is lined up with the center line on the front panel, and to make sure the projector’s air vents can get some circulation. The small circular posts are for holding the Pi, and the slot along the front will hold the front panel. The large circular hole is where I was originally going to put the power switch, and all the tiny holes are the screw holes.
Here is my first test fitting of the electronics on the base:
The projector fit perfectly, but the Pi was hanging over the back edge just a hair. In addition I decided I wanted the Pi farther back so that I had more room to attach the handle to the top and bottom plates. Keen observers will also notice the missing mounting post for the Pi; it broke off while I was trying to screw the Pi down.
After a couple more tries I had a winner:Here you can also see the right-angle micro-USB connector I found on Amazon. By pure luck it is exactly the right size so that it lines up with right edge of the gun, meaning I would be able to charge the projector without opening the gun.
It’s at this point that I hit my first snag. The HDMI ribbon cable was built with right-angle connectors, which was fine on my original design, but with the Pi partially underneath the projector the connector on the Pi end did not have enough room. So, back to Adafruit i went for a straight connector.
Next up were the side pieces. These would need to have small tabs to allow them to be screwed to the top and bottom plates, and would also need some carefully positioned access slots in them for the projector’s side controls and the micro USB charging connector. This was a bit tricky because the corners and edges of the projector are rounded just enough to make it difficult to get an accurate measurement with my digital caliper. I went through several iterations of the side panels before finally coming up with ones that fit; fortunately they are small and printed fast.
Here’s the partially-assembled gun with the side panels attached:
Next up was the top panel. This was actually the simplest piece to print because it only had two openings beside the screw holes, and the placement of those two openings was rather arbitrary:
And here’s the top with the display and the portal fluid cylinder mounted:
Perfect! In fact the display actually just snaps in place on its own; originally I had intended to drill some small holes and secure it with screws, but i broke my 1.1mm drill bit so I just left it as-is.
Last, but not least, I printed the front plate. I did this last because it’s black and I didn’t want to change the filament in the printer until I was done printing the white pieces. I also printed two domes out of translucent green filament and mounted those in the front panel. The domes have a hollow space inside that is just large enough for an LED. Note that there are three holes but only two are filled; the third hole is the output for the projector.
Finally here’s the body mostly assembled, minus the yet-to-be-printed handle. The top isn’t screwed down yet because I still need to fill the portal fluid cylinder and also do all of the LED wiring.
Going into this I knew what the handle should look like, but I had no idea how to design it. It took me the better part of a day to design this one piece, and it was the most frustrating day of the entire project. The handle, with its non-square angles and curves, was well beyond anything I had ever done in FreeCAD before.
I am not going to go into too much detail on the handle design because I was learning as I went and so what I did may not be the best way to do things (and I don’t even remember all the steps now!) But the simple version is that it consists of a half cylinder base with a hollow area for wiring, and then a cylinder set at an angle as the actual handle. Two angled cylindrical shafts, one from the top and one from the bottom, provide mounts for the control knob and power switch:
Unfortunately my measurements for those access shafts were a bit tight so I had to carefully drill them out to make room.
With the software done and all the pieces designed and printed it was time for final assembly.
I started with the portal fluid. For this I used some clear Aloe Vera gel to provide a cool bubble effect. I also drilled two small holes in the lid for the leads of an LED (after making sure the lid was non-conductive of course!). I mounted a super-bright green LED on the inside of the lid and secured it with more Loctite.
Next I glued LEDs in each of the green domes on the front panel, and then wired them all in parallel along with some 200 ohm current-limiting resistors. All connections are soldered and covered in heat-shrink tubing for strength. The whole LED circuit is then connected to 5V and GND on the Pi. As long as the Pi is powered on the LEDs will be lit.
Once the wiring for the LEDs was done I permanently attached the portal fluid cylinder to the top panel with some Loctite:
Next I connected the top display to the I2C and power pins on the Pi. The display requires two power connections; a 5V supply, and a supply line tied to the desired voltage level of the I2C pins, which in the case of the Pi is 3.3V.
After the display was connected I turned to the handle. First up was the rotary encoder. It requires five wires: three for sensing rotation and one for the pushbutton function. Two of these would go to ground and the rest to GPIO inputs. Once it was connected I carefully mounted it in its access shaft on the handle, taking care not to break the connections.
Next I cut the ends off of a USB-A to micro-USB cable and wired them together with the power switch in series, then plugged one end into the projector and the other into the Pi. I then mounted the switch inside the shaft I made for it on the bottom of the handle.
The final step was to assemble the remaining pieces and test the portal gun. I slotted the front panel in its mounting slots, and then screwed the lid down to the body. Then I carefully pushed the handle into place, taking care not to break any of the wiring coming from the controls on the handle, and screwed it to the top and bottom panels. Here is my first power on test:
As you can see there is one TINY thing missing, and that is the red filter over the display. I bought some red plastic sheets on Amazon and cut them to size, doubling them up to produce a deeper red. I also printed a simple black frame to go around the display, and carefully glued both in place with Loctite.
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:
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.
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!