Now I can control my LED Christmas Tree from DOS! 🎄💾 I hope to share more details on the code + dev stack, but basically I used:
- Open Watcom V2
- Packet drivers
- mTCP
- 86Box + Windows 11 for development
- A Gateway 2000 ColorBook 486 for the final test 😎
Now I can control my LED Christmas Tree from DOS! 🎄💾 I hope to share more details on the code + dev stack, but basically I used:
Back around the time the first iPhone was released (feeling old! 😬) I was taking a course where we built a CPU-based ray tracer in C.
If you’re not familiar with the ray tracing technique, check it out here.
What I mostly remember from the course was math, pointers, and segfaults. Oh the segfaults. By the end of the course, however, I had a decent grasp on C and that’s been a valuable skill so many times in my career and hobbies.
Recently I decided that I wanted to learn more about the inner workings of WebAssembly (Wasm) and figured this would be a great candidate project. It’s fully contained without any external dependencies, *I wrote all the code so it shouldn’t be too mysterious, and if I got it to work there would be a visual payoff.
*Feel free to judge some of the rough spots in the code – it was a long time ago!
The first thing I made sure of was that I could compile the project locally the non-Wasm way. There were no hiccups there – it worked on the first try using the Makefile
. ✅
I then started reading this tutorial on converting a C project to Wasm. After installing emscripten on macOS (I used Homebrew) I decided to add a new C source file to the project and added a function that looked something like:
#include "emscripten.h"
EMSCRIPTEN_KEEPALIVE
int version() {
return 42;
}
If I could get this to work I could at least get information from C -> JS for starters. All that it took to make this work was:
gcc
with emcc
in the Makefile
EXPORTED_RUNTIME_METHODS='["cwrap"]'
compiler flagModule.cwrap
from JS to use the functionThat was pretty much it. I’m not going to go super in-depth with this blog post because I think most of it can be figured out from the source.
I had a bit more to go but was surprised at how easy it was to send a value from C to JS. The next items to figure out were:
fprintf
and its siblings go when trying to debug to stdout
and stderr
?main
– does it run?I’ll go ahead and spoil these really quickly in their respective order:
char *
) and providing a FILE
type in return which is an in-memory buffer stream. In other words, no massive overhauling needed although we aren’t using “real” files anymore. In addition a slight refactoring was done to the project to return an array of pixels rather than write out an image file.int
. It then is able to initialize an array of UInt8
s.stderr
calls are even properly displayed as errors.Makefile
to use emcc
.main()
because I didn’t need it.char
array.pixel
struct to include an alpha channel for the expected RGBA format. Yay for properly using sizeof
throughout the code.That’s mostly it! Check out the GitHub repo here. 🚀
I’m starting to dust off some seasonal projects and realized I hadn’t made this simple tool public which others may find handy. With projects like the NeoPixel Tree it can be much quicker to code visual sequences locally instead of waiting for new firmware to upload to the MCU every time you want to tweak something.
The tool just wraps around the Adafruit GFX Graphics Library and instead of outputting to physical pixels it runs through SDL2. It’s somewhat similar to what I did in swift-gfx-wrapper but keeps it all in C.
GitHub repo: https://github.com/twstokes/gfx-proto
Maybe if I share videos of half-finished projects it’ll motivate me to finish them!
From the weekend hacks department: I now have DOOM running on my 64×64 matrix!
GitHub repo: https://github.com/twstokes/doom-matrix
Fun fact: You can put the latest version of OpenBSD on a PPC 32-bit processor like the G4. Fun to dual boot with Mac OS 9 if you want a modern, secure computer!
The OpenBSD docs are really good and thorough. Open Firmware needs some tweaking if you want to boot directly into OpenBSD, so this is what I did after booting into it with command+option+o+f
:
setenv auto-boot? True
setenv boot-device hd:,ofwboot
reset-all
Initially I didn’t want to mess with the internal drive of the iMac since I had both Mac OS 9 and Mac OS X installed, so I tried to install to a USB drive. Although the installation succeeded (albeit extremely slowly due to USB 1.1), the boot into the system failed due to the following error:
panic: rootfilesystem has size 0
Looking at the trace of the kernel boot process it was evident why: Even though we installed the OS to sd0
(the mounted USB device), the kernel kept trying to mount wd0
which is the internal IDE drive.
I tried what I knew:
boot-device
variable in Open Firmwarebsd.rd
) and mounting the USB to see if I could tweak fstab
Supposedly if we get to the boot
prompt we can pass a -a
flag for the root device (docs), but I couldn’t figure out how to get there.
Ultimately I decided to install OpenBSD to the main internal drive for now. If I get a hankering for Mac OS 9 I still have the trusty Power Mac G4.
The best setup will eventually be a dual or triple-boot. Trying to make the super-slow USB drive work is probably a terrible idea unless we plan to run it in a ramdisk mode the entire time.
As you can see from the glxgears
output above graphics are not accelerated. I’ve mostly played with the machine over SSH in a headless state so this hasn’t bothered me too much. I did glance at dmesg
and saw that the expected driver, nv
, was loaded and detected the card so I’m not totally sure what’s happening. I’m having flashbacks of when I used to spend hours tweaking xorg.conf
and that may be on the horizon again.
If just running the console we still want the screen to sleep and I found I needed to make a couple tweaks for that to work.
First I needed to shut down X Windows:
rcctl stop xenodm
Then I needed to disable output activity from waking the screen:
display.outact=off
After that the screen would shut off after however many milliseconds were set for display.screen_off
.
Copying over /etc/examples/wsconsctl.conf
to /etc/
is a great starter config.
If you’re running a G4 iMac 15″ that’s less than 1GHz, you have the GeForce2 MX which doesn’t have support out of the box via the nouveau
driver. This means an unaccelerated graphics environment, low framerates, and sometimes a console that has inverted colors making it really hard to use.
The GeForce4 MX integrated on the 1GHz 15″ model and most of the 17″ iMacs is supported.
glxgears
at a blazing 12FPS.(Very poorly, presumably until the graphics driver is tweaked)
Running Chocolate Doom was painful. Even the setup utility had a good second or so input lag!
I first want to acknowledge that I did the thing that I try to never do: I showed off a snazzy project, left some hints here and there of how it worked, said I would follow up with full details… and never did. That’s lame.
I’ve had multiple people reach out for more info and I’m glad they did, since that’s pushed me to finally get some repos public and this belated follow-up written. Apologies!
To jump straight to it, I’ve published these two repos:
Let’s first go over the hardware involved. The most important piece, of course, is the Alfa-Zeta XY5.
In my case, the 14×28 board was made up of two 7×28 panels connected together via RJ-11.
The panels are pricey, but they can be thought of as “hardware easy-mode”. Alfa-Zeta has done the hard job building the controller that drives the hardware and all we have to do is supply power and an RS-485 signal that abides by their protocol.
If you purchase a panel from them there are two important documents to request:
These can easily found by searching around, but if you own a panel the company should supply them. Most of the protocol can be deduced by looking at open source code.
The 24V -> 5V converter isn’t necessary if you supply power to the MCU independently, say through a USB power adapter.
VCC -> 3.3v
Gnd -> Gnd
DE -> 3.3v pulled high because we're always transmitting
RE -> 3.3v pulled high because we're always transmitting
DI -> TX[x] x being 0 or higher depending on board
RO -> RX[x] most boards only have the main serial IO, but boards like the Mega have multiple
An Arduino Mega is driving the board in this photo.
See https://github.com/twstokes/flipdots for the code that runs on the MCU.
At the moment there isn’t much to it – you can either compile the firmware to run in a mode that writes data from UDP packets to the board, or you can draw “locally” using Adafruit GFX methods.
See the README in the repo above for more details.
See https://github.com/twstokes/flipdots-ios for the code that runs on these devices.
Semi-interestingly I utilized Adafruit GFX again, this time via swift-gfx-wrapper to draw to the board over UDP. It’s hacky and experimental, but that’s part of the fun.
See the README in the repo above for more details.
The Power Mac G4 didn’t get the “windtunnel” nickname for nothing – its power supply is quite loud. Thankfully with the help of an adapter, a standard ATX (or SFX) power supply can replace it. I love putting “modern” power supplies into my retro machines to get less noise and clean power.
I went with a Corsair SF600 from my previously built Mini-ITX machine and it’s worked really well due to its small form factor. Although it’s rigged in place with two wire ties it’s not going anywhere. 😀
Resources:
From the seasonal hacks department, here’s my toy app to make it snow on macOS. ❄️
https://github.com/twstokes/snowflakes
When the app is told to make it snow it adds full-screen non-interactive windows on each display and inside those windows adds a SpriteKit view with a scene inside that contains emitters.
That’s basically it!
Thanks to Whisper and this awesome port, the tree is responding to spoken words. 🗣🎄
Since the tree itself only has a low-powered MCU, we need another machine to act as a listener.
The architecture is:
For now I’m running it from iOS and macOS, so I wrote the current implementation in Swift. The code is currently still in “hack” status, but working well!
Now it’s time to test it when talking to coworkers at Automattic.