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

June 6, 2020 by Sven Gregori 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.

Continue reading “64-bit And A Display: Minecraft Computers 10 Years Later” →

Breadboard Computer Plays Snake On Character Display; Also In A Browser!

April 26, 2020 by Sven Gregori 4 Comments

If building a homebrew computer on a breadboard is your thing, you’re most certainly familiar with [Ben Eater], whose design of using nothing but logic gates has served as inspiration for many replicas over the years. [visrealm] took the concept and expanded upon it, even adding a 16×2 LCD that let’s you play Snake by moving a single pixel on the character display!

Making the most of tiny resolution is impressive — it’s a difficult constraint for the game field. But there are other tricks at work as well. [visrealm] uses different intensities to distinguish between the snake and its food which is kind of a dark pixel in the demo shown after the break. But what stands out most is that the breadboard build is really only half of the story. In addition, [visrealm] built an entire emulator that resembles his actual breadboard design, which can be programmed and used via browser, giving WebAssembly a whole new meaning. While that’s convenient for anyone interested to play around with these breadboard computers, but lacks the patience to build one themselves, it also functions as the real one’s programming environment. In addition, an ESP8266 is used to load a new program directly via WiFi.

All the code and some build notes are available on GitHub, and if you’re looking for a nifty LCD emulator for your web site, there’s a standalone repository for that as well. But in case you need a better display option for your own breadboard computer, how about adding a VGA connector? And if you don’t build your own yet, it’s never too late to start.

Continue reading “Breadboard Computer Plays Snake On Character Display; Also In A Browser!” →

FPGA 6800 Uses Python Toolbox

December 27, 2019 by Al Williams 7 Comments

Usually, when you think of designing — or recreating — a CPU on an FPGA, you assume you’ll have to use Verilog or VHDL. There are other options, as well, but those are the biggest two players in FPGA configuration. [Robert Baruch] has a multipart series where he uses nMigen — a Python toolbox — to recreate a 6800 CPU like the one used in many vintage video games and pinball machines.

Unlike some tools that try to convert software written in some language to an FPGA configuration, nMigen uses Python as a scripting language to create code in FHDL. This is similar in concept to VHDL or Verilog, but gives up the event-driven paradigm, opting instead to allow designers to explicitly call out synchronous and combinatorial logic.

Continue reading “FPGA 6800 Uses Python Toolbox” →

This CPU Has Only One Instruction

December 7, 2019 by Jenny List 37 Comments

Most of us will be familiar at some level with the operation of a basic CPU, usually through exposure to microprocessors of the type that find their way into our projects. We can look at its internal block diagram and get how it works, see the registers and ALU, follow the principles of a von Neumann architecture, and understand that it has an instruction set with different instructions for each of its functions. We all know that this only describes one type of CPU though, and thus it’s always interesting to see alternatives. [Ike Jr] then has a project that should provide a lot of interest, it’s a CPU that only has a single instruction. It can only move data from one place to another, which seems to preclude any possibility of computation. How on earth can it work?

The machine has a set of registers as well as memory, and it achieves computation by having specific registers where we might expect to see instructions. For example the AND register is a two-position stack, that when it is full computes the AND of its two pieces of data and places the result in a general purpose register. The write-up goes into significant detail on the CPU’s operation, and while it’s unlikely the world will move en masse to this architecture it’s still a very interesting read. For now this is a machine that exists in software simulation rather than in silicon, and he’s working to release it so enthusiasts for unusual CPUs can have a go.

The idea of having registers that compute reminds us of a transport triggered architecture machine, being not the same as a one instruction CPU with a more conventional computing instruction.

Abstract PCB header image: Harland Quarrington/MOD [OGL v1.0].

SPARC CPU In A Cheap FPGA

November 1, 2019 by Al Williams 12 Comments

There was a time when SPARC CPUs were the sole realm of pricey Sun workstations, but now you can put one on an FPGA with just a little trouble. The problem is you need a fairly big FPGA which isn’t always cheap unless someone goes out of business and you get lucky. [Ttsiodras] picked up a Pano logic thin client. Pano went under and their entire inventory is out on the surplus market at cheap prices. With a little FPGA magic, you can turn a few bucks into a SPARC-based computer.

The insides of the workstation have a Spartan 6 FPGA inside and you’ll need to solder in some JTAG wires, but that shouldn’t put anybody here off. Of course, the Spartan 6 isn’t the newest tech so you’ll have to get an old version of the Xilinx tools but that’s not hard either. However, there is a strange irony you’ll need to be aware of if you use Linux.

Continue reading “SPARC CPU In A Cheap FPGA” →

Proprietary Fan Blows, Gets PWM Upgrade

October 26, 2019 by Bryan Cockfield 13 Comments

Proprietary components are the bane of anyone who dares to try and repair their own hardware. Nonstandard sizes, lack of labeling or documentation, and unavailable spare parts are all par for the course. [Jason] was unlucky enough to have an older Dell computer with a broken, and proprietary, cooling fan on it and had to make some interesting modifications to replace it.

The original fan had three wires and was controlled thermostatically, meaning that a small thermistor would speed up the the fan as the temperature increased. Of course, the standard way of controlling CPU fans these days is with PWM, so he built a circuit which essentially converts the PWM signal from the motherboard into a phantom thermistor. It’s even more impressive that it was able to be done with little more than a MOSFET and a Zener diode.

Unfortunately, there was a catch. The circuit only works one way, meaning the fan speed doesn’t get reported to the motherboard and the operating system thinks the fan has failed. But [Jason] simply disabled the warning and washed his hands of that problem. If you don’t want to use a CPU fan at all, you can always just dunk your entire computer in mineral oil.

The Smallest Homebrewed TTL CPU In The World

October 16, 2019 by Sharon Lin 16 Comments

This may very well be the smallest homemade TTL CPU we’ve ever seen. Measuring at one square inch, this tiny chip boasts 40 connections, an 8-bit databus, a 16-bit address bus, a 64 kB memory space, reset and clock inputs, and 5 V power lines.

TTL (transistor transistor logic) logic chips are pretty outdated today, but they do have all of the basics necessary for building a computer – logic gates, counters, buffers, and registers. The transistors perform both the logic and amplifying, as compared to resistor-transistor logic (RTL) and diode-transistor logic (DTL). In the 60s, when the technology was still fairly new, TTL ICs were commonly used in computers and industrial controls. Even after the advent of VLSI, TTL ICs were still being used for interfacing more densely integrated chips. Even so, most TTL chips tend to be on the bulkier side, which is what makes [roelh]’s project so unique. The entire PCB is hardly any larger than a coin.

On top of the hardware specs, [roelh] also implemented several useful software features: zero page addressing, load/store/compare instructions, stacks, conditioning branching, subroutine calls, and memory-mapped I/O. The registers are also in RAM, which has been implemented in microprocessors in the past (see TMS9900) for speed considerations, but in this case was implemented for size constraints.

An ALU was also left out of the design in order to constrain its size, leaving only 8 ICs on either side of the 2-layer PCB.

Microprograms are stored in Flash memory and can be programmed with a Raspberry Pi. by saving the Assembly code to a memory card and downloading the assembled binary code. Once the Raspberry Pi is connected to the development board, you can burn the binary code onto the Flash memory of the board using a Python script. An online Javascript editor also exists for assembling the Assembly code for the chip and simulating the CPU.

There is currently a development board made for the CPU, which includes six seven-segment displays and an I/O connector for running a digital clock and other applications. [roelh] has since built a retro TTL computer around the chip, which reintroduces the ALU and includes address registers, 256 KB of RAM, VGA video, PS/2 keyboard port, a sound system, and I/O pins. It’s a really exciting project that’s seriously pushing the constraints of retro computing.