homebrew cpu

10 Articles

64-bit And A Display: Minecraft Computers 10 Years Later

June 6, 2020 by 6 Comments

Some people build their own computer to play games, while others play games to build their own computer. Minecraft is the prime candidate for the latter, and while you can certainly arrange the blocks to make them look like a computer, we’re of course talking about replicating the actual functionality of a CPU or parts thereof, and/or external components within the game. Many such creations have spawned in the decade since the first Minecraft-built ALU surfaced, and [Rockfarmor] built a 64-bit specimen to add to that list — and made a video to showcase it.

Instead of emulating a common architecture, [Rockfarmor] went for a more home-made approach, and re-used the architecture from an old school assignment (in Swedish) as basis. The result is a simple yet fully functional 64-bit CPU with 32 registers, 32kB main memory and a separate 16kB stack. The instruction set mostly contains ALU and branching operations, but also a few special opcodes to control an additional 64×64 pixel blocks, 64-color display — including drawing circles, lines, and color fills.

More details on the architecture can be found in its documentation and in an older video (with subpar audio circumstances unfortunately). An additional time-lapse video of the initial build is also available, and you will find all of them after break. To simplify development, [Rockfarmor] also wrote a desktop app to program the computer in assembly and upload it straight to the Minecraft version.

As with all computers built in Minecraft, the driving force is redstone, which essentially allows circuit design within the game, and [Rockfarmor]’s is no difference here. He also uses command blocks to avoid the laboriously and slow “wiring” required otherwise, turning it more into a “wireless redstone” circuit.

No doubt, purists will consider this cheating, but another angle would be to see it as Moore’s Law applied to Minecraft computers, considering the computer’s size and speed compared to the first Minecraft ALU. Or maybe as the equivalent of microcode in real-world CPUs? Or then, maybe we should just accept and embrace different options and preferences.

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An 8-Bit Transport Triggered Architecture CPU In TTL

April 21, 2017 by 37 Comments

When we are introduced to the internals of a microprocessor, it is most likely that we will be shown something like one of the first generation of 8-bit CPUs from the 1970s. There will be the familiar group of registers and counters, an arithmetic and logic unit (ALU), and an instruction decoder with associated control logic. A complex instruction set causes the decoder to marshal registers and ALU to perform all the various functions in the right order. CPUs may have moved on in many ways since the 1970s, but the block diagram of an 8080 or similar still provides a basic grounding for the beginner.

So when we tell you about another home-made CPU using TTL logic chips, you might expect it to follow this well-worn path. Fortunately though the hardware hacking community is always capable of springing surprises upon us, and [Szoftveres] has done just that with his design. It’s a one-instruction-set machine following a transport triggered architecture, and that means it deviates sharply from the conventional architecture described above. Each instruction is a move between the different physical functions of the processor, and computation is achieved by the physical functions working on the data as it is moved into them and presenting the result on their outputs ready to be moved elsewhere. The result is a computer that is in its own way beautifully simple, though at the expense of some inflexibility and lack of some hardware functions we take for granted in more conventional processors.

This machine has been built on a piece of stripboard, and has an accompanying board with display, keypad, and a modem. There is a small board based upon an ATmega8 microcontroller which performs the function of fast program loading, and can be removed once the code is loaded. Software can be written in a C-like language anc compiled using the compiler in his GitHub repository, and he has produced a YouTube video of the machine in operation. This project is well worth reading through in-depth, for its introduction to this slightly unusual architecture.

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Weird CPU

August 6, 2016 by 24 Comments

How many instructions does [agp.cooper’s] computer have? Just one. How many strip boards does it use? Apparently, 41 five 41-track boards. While being one shy from the answer to life, it is still a lot of boards for a single instruction. The high board count is due to the use of 1970’s vintage ICs including TTL parts, 2114 RAM chips, and 74S571 PROMs.

There are several different architectures for single instruction computers and [agp’s] uses what is technically at TTA (transfer-triggered architecture). That is, the one instruction is a move and the destination or source of the move determines the operation. For example, the Wierd CPU (that’s the name of it) has a P and Q register. If you load those registers and then the ADD register will contain the sum of the two numbers.

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