He also did run into a similar problem that I ran into when I tried something like that as well: Sound Chips. Building a system around a Yamaha FM Synthesizer is perfect, but I found as well that most of the chips out there are broken, fake, or both and that no one else makes them anymore. Which makes sense because if you want a sound chip in this day, you use an AC97 or HD Audio codec and call it a day, but that goes against that spirit.
I think that the spirit on hobby electronics is really found in FPGAs these days instead of rarer and rarer DIP parts. Which is a bit sad, but I guess that's just the passage of time. I wonder if that's how some people felt in the 70s when CPUs replaced many distinct layouts, or if they rejoiced and embraced it instead.
I've given up trying to build a system on a breadboard and think that MiSTer is the modern equivalent of that.
Microcontrollers have taken over. When 8kB SRAM and 20MHz microcontrollers exist below 50-cents and at miniscule 25mm^2 chip sizes drawing only 500uA of current... there's very little reason to use a collection of 30 chips to do equivalent functionality.
Except performance. If you need performance then bam, FPGA land comes in and Zynq just has too much performance at too low a cost (though not quite as low as the microcontroller gang).
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Hobby Electronics is great now. You have so many usable parts at very low costs. A lot of problems are "solved" yes, but that's a good thing. That means you can focus on solving your hobby problem rather than trying to invent a new display driver or something.
I do think some people that remember fondly the user experience of those old machines might be better served by using modern machines (like a raspberry pi or even a standard pc) in a different way instead of trying to use old hardware. That's from the good old Turing machine universality (you can simulate practically any machine you like using newer hardware, if what you're interested in is software). You can even add artificial limitations like PICO-8 or TIC-80 does.
See also uxn:
and (WIP) picotron:
https://www.lexaloffle.com/picotron.php
I think there's a general concept here of making 'Operating environments' that are pleasant to work within (or have fun limitations), which I think are more practical than a dedicated Operating System optionally with a dedicated machine. Plus (unless you particularly want to!) you don't need to worry about all the complex parts of operating systems like network stacks, drivers and such.
[1] Maybe we should call that Hobby universality (or immortality?) :P If it's already been made/discovered, you can always make it again just for fun.
Edit: found it! https://excamera.com/sphinx/gameduino/index.html
A FPGA is really just the right tool for solving the video problem. Or some projects do it with a micro-controller. But it's sort of too bad as it kind of undercuts the spirit of the whole design. If you video processor is orders of magnitude more powerful than the rest of the computer, then one starts to ask why not just implement the entire computer inside the video processor?
And yeah, you can't really buy sprite-based video chips anymore, and you don't even have to worry about stuff like "Sprites per Scanline" because you can get a proper framebuffer for essentially free - but now you might as well go further and use one microprocessor to be the CPU, GPU, and FM Synthesizer Sound Chip and "just" add the logic to generate the actual video/audio signals.
https://github.com/studio8502/Sentinel-65X
It's not yet a deliverable product but watching the developers work on it has been an entertaining part of my doomscrolling diet.
I always got the impression that David sort of got railroaded by the other members of the team that wanted to keep adding features and MOAR POWAH, and didn't have a huge amount of choice because those features quickly scoped out of his own areas of knowledge.