Build Your Own CPU? That’s the Easy Part!

You want to build your own CPU? That’s great fun, but you might find it isn’t as hard as you think. I’ve done several CPUs over the years, and there’s no shortage of other custom CPUs out there ranging from pretty serious attempts to computers made out of discrete chips to computers made with relays. Not to trivialize the attempt, but the real problem isn’t the CPU. It is the infrastructure.

What Kind of Infrastructure?

I suppose the holy grail would be to bootstrap your custom CPU into a full-blown Linux system. That’s a big enough job that I haven’t done it. Although you might be more productive than I am, you probably need a certain amount of sleep, and so you may want to consider if you can really get it all done in a reasonable time. Many custom CPUs, for example, don’t run interactive operating systems (or any operating system, for that matter). In extreme cases, custom CPUs don’t have any infrastructure and you program them in straight machine code.

Machine code is error prone so, you really need an assembler. If you are working on a big machine, you might even want a linker. Assembly language coding gets tedious after a while, so maybe you want a C compiler (or some other language). A debugger? What about an operating system?

Each one of those things is a pretty serious project all by itself (on top of the project of making a fairly capable CPU). Unless you have a lot of free time on your hands or a big team, you are going to have to consider how to hack some shortcuts.

Continue reading “Build Your Own CPU? That’s the Easy Part!”

8-bit logic chip computer build

[Kyle] has been hard at working building an 8-bit computer from the ground up. He’s using a set of logic IC’s for the various components, and some NVRAM chips to store the control words. What you see above is the roadmap for his instruction set. He’s just started writing them to the chips, making the job easier by building an Arduino-based programmer.

We’ve enjoyed watching [Quinn Dunki’s] progress with her Z80  6502-based PC build which started on a breadboard in much the same way but has come a long way since those humble beginnings. Recently we also looked in on a 4-bit computer that is using discrete components. But [Kyle’s] take on the challenge falls somewhere in between the two.

The gist of his design can be found in one of his earlier post. He’s got a ring counter which starts by clearing the address register. It then loads the NVRAM address of the next instruction which is then executed on the subsequent count. It seems the build still has some way to go so make sure to keep your eye out for updates.

[via Reddit]