Every time we say “We’ve seen it all”, along comes a project that knocks us off. 60 year old [Mark Nesselhaus] likes to learn new things and he’s never worked with hardware at the gate level. So he’s building himself a 4-bit Computer, using only Diode-Transistor Logic. He’s assembling the whole thing on “card board” perf-board, with brass tacks for pads. Why — because he’s a thrifty guy who wants to use what he has lying around. Obviously, he’s got an endless supply of cardboard, tacks and Patience. The story sounds familiar. It started out as a simple 4-bit full adder project and then things got out of hand. You know he’s old school when he calls his multimeter an “analog VOM”!
It’s still work in progress, but he’s made a lot of it in the past year. [Mark] started off by emulating the 4-bit full adder featured on Simon Inns’ Waiting for Friday blog. This is the ALU around which the rest of his project is built. With the ALU done, he decided to keep going and next built a 4-to-16 line decoder — check out the thumbnail image to see the rats nest of jumbled wires. Next on his list were several flip flops — R-S, J-K and D types, which would be useful as program counters. This is when he bumped into problems with signal levels, timing and triggering. He decided to allow himself the luxury of adding one IC to his build — a 555 based clock generator. But he still needed some pulse shaping circuitry to make it work consistently.
[Mark] also built a finite-state-machine sequencer based on the work done by Rory Mangles TinyTim project. He finished building some multiplexers and demultiplexers, and it appears he may be using a whole bank of 14 wall switches for address, input and control functions. For the output display, he assembled a panel using LED’s recovered from a $1 Christmas light string. Something seems amiss with his LED driver, though — 2mA with LED on and >2.5mA with LED off. The LED appears to be connected across the collector and emitter of the PNP transistor. Chime in with your comments.
This build seems to be shaping along the lines of the Megaprocessor that we’ve swooned over a couple of times in the past. Keep at it, [Mark]!
[F4HDK] calls his new computer A2Z because he built everything from scratch (literally, from A to Z). Well, strictly speaking, he did start with an FPGA, but you have to have some foundation. The core CPU is a 16-bit RISC processor with a 24-bit address bus and a 128-word cache. The computer sports 2 megabytes of RAM, a boot ROM, a VGA port and keyboard, and some other useful I/O. The CPU development uses Verilog.
Software-wise, the computer has a simple operating system, a filesystem, and basic programs like a text editor and an image viewer. Development software includes an assembler and a compiler for a BASIC-like language that resides on the PC. You can also run an emulator to experiment with A2Z without hardware. You can see a “car game” running on A2Z in the video below. You can also see videos of some other applications.
Now, over the holiday season there seems to be a predilection towards making merry and bright. As many an engineer and otherwise are sure to note, fine alcohols will facilitate this process. One such warm holiday beverage is mulled wine; there are many traditions on how to make it, but a singular approach to preparing the beverage would be to re-purpose an old PC and a CPU liquid cooling unit into a mulled wine heating station.
Four years ago, [Adam] found himself staring at a pile of mostly obsolete PCs in his IT office and pondering how they could be better used. He selected one that used a power-hungry Pentium 4 — for its high heat output — strapped a liquid cooling block to the CPU and pumped it full of the holiday drink. It takes a few hours to heat three liters of wine up to an ideal 60 Celsius, but that’s just in time for lunch! The Christmastime aroma wafting through the office is nice too.
There is a certain benefit to being an early adopter. If you were around when Unix or MSDOS had a handful of commands, it wasn’t hard to learn. Then you learn new things as they come along. If you started learning Linux or Windows today, there’s a huge number of details you have to tackle. You have the same problem trying to learn CPU design. Grappling with the design of a 16-bit CPU with a straightforward data path is hard enough. Throw in modern superscalar execution, pipelining, multiple levels of microcode, speculative execution, and all the other features modern processors have and you’ll quickly find yourself lost in the details.
[Michai Ramakers] wanted to build an educational CPU and he took a novel approach. The transistor CPU uses only one instruction and operates on one bit at a time. Naturally, this leads to a small data path, which is a good thing if you’re only using discrete transistors. His website is a ground-up tutorial in building and using the tiny computer.
[Agp.cooper] saw a vintage 4Kx4 bit RAM chip and decided that it needed a CPU design to match. The TTL design fits on two boards and has a functional front panel.
This custom CPU project has a few interesting bits worth noting. First, it is small enough that you can wrap your head around it pretty easily. And [Agp.cooper] gives a good account of the instructions set architecture choices he considered and why he settled on the final design.
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.
Often, CPUs that work together operate on SIMD (Single Instruction Multiple Data) or MISD (Multiple Instruction Single Data), part of Flynn’s taxonomy. For example, your video card probably has the ability to apply a single operation (an instruction) to lots of pixels simultaneously (multiple data). Researchers at the University of California–Davis recently constructed a single chip with 1,000 independently programmable processors onboard. The device is energy efficient and can compute up to 1.78 trillion instructions per second.
The KiloCore chip (not to be confused with the 2006 Rapport chip of the same name) has 621 million transistors and uses special techniques to be energy efficient, an important design feature when dealing with so many CPUs. Each processor operates at 1.78 GHz or less and can shut itself down when not needed. The team reports that even when computing 115 billion instructions per second, the device only consumes about 700 milliwatts.
Unlike some multicore designs that use a shared memory area to communicate between processors, the KiloCore allows processors to directly communicate. If you are just a diehard Arduino user, maybe you could scale up this design. Or, if you want to make use of the unused power in your video card under Linux, you can always try to bring KGPU up to date.