A TTL CPU, Minimising Its Chip Count

By now we should all be used to the astonishing variety of CPUs that have come our way created from discrete logic chips. We’ve seen everything from the familiar Von Neumann architectures to RISC and ever transport-triggered architecture done in 74 TTL derivatives, and fresh designs remain a popular project for many people with an interest in the inner workings of a computer.

[Warren Toomey]’s CSCvon8 is an interesting machine that implements an 8-bit computer with a 64-bit address space using only 17 chips, and without resorting to any tricks involving microcontrollers. It implements a fairly conventional Von Neumann architecture using TTL with a couple of tricks that use modern chips but could have been done in the same way in decades past. Instruction microcode is stored in an EEPROM, and the ALU is implemented in a very large EPROM that would probably once have been eye-wateringly expensive. This in particular removes many discrete TTL chips from the total count, in the absence of the classic 74181 single-chip part. To make it useful there is 32k each of RAM and EEPROM, and also a UART for serial access. The whole is brought together on a neat PCB, and there is a pile of demo code to get started with. Everything can be found in the project’s GitHub repository.

At the start of this article we mentioned a couple of unconventional TTL CPUs. The transport triggered one we featured in 2017, and the RISC one is the Gigatron which has appeared here more than once.

FPGA Soft CPU Is Superscalar

We will admit it: mostly when we see a homebrew CPU design on an FPGA, it is a simple design that wouldn’t raise any eyebrows in the 1970s or 1980s. Not so with [Henry Wong’s] design, though. His x86-like design does superscalar out-of-order execution, just like big commercial modern CPUs. Of course [Henry] designs CPU architectures for Intel, so that’s not surprising. You can see a very detailed talk on the design in the video, below. You can also read the entire thesis project.

[Henry] starts out with a description of FPGAs and soft processors. He also covers the use of multiple instruction issue to increase the virtual clock rate of a CPU. In other words, if a 100 MHz CPU can do one instruction at a time, it won’t be any faster — in theory — than a 50 MHz CPU that can do two instructions at once. Of course, trying to do two at once has some overhead, so that won’t be completely true.

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CPU Made From 74HC Chips Is A Glorious Mess

Did you ever start a project that you felt gained a life of its own? This project by [Paulo Constantino] is an entire CPU named dreamcatcher on breadboards, and is a beautiful jungle of digital. On top of that, it works to connect to an analog VGA display. How cool is that!

Designing an ALU and then a CPU is a typical exercise for students of digital design and is done using VerilogHDL or VHDL. It involves creating an ALU that can add, subtract etc while a control unit manages data moves and the like. There is also a memory fetch and instruction decode made up of de-mulitiplexers and a bunch of flip-flops that make up registers and flags. They are as complex as they sound if not more.

[Paulo Constantino] went ahead and designed the whole thing in Eagle as a schematic using 74HC logic chips. To build it though instead of a PCB he used breadboards. Everything from bus decoders to controlling an external VGA display is done using jumper wires. We did cover a video on the project a while back, but this update adds a video card interface to the build.

The CPU updates the display buffer on the VGA card, and in the video below shows the slow and steady update. The fact that the jungle of wires can drive a display is awesome. He has since started working on a 16-bit version of the processor and we’d love to see someone take it up a notch.

For those more accustomed to the PCB, the Z80 membership card project is a great build for 8-bit computer fans.

Thanks to [analog engineer] for the tip.

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Getting Started With Free ARM Cores On Xilinx

We reported earlier about Xilinx offering free-to-use ARM Cortex M1 and M3 cores. [Adam Taylor] posted his experiences getting things working and there’s also a video done by [Geek Til It Hertz] based on the material that you can see in the second video, below.

The post covers using the Arty A35T or Arty S50 FPGA boards (based on Artix FPGAs) and the Xilinx Vivado software. Although Vivado will allow you to do conventional FPGA development, it also can work to compose function blocks to produce CPUs and that’s really what’s going on here.

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Foreshadow: The Sky Is Falling Again For Intel Chips

It’s been at least a month or two since the last vulnerability in Intel CPUs was released, but this time it’s serious. Foreshadow is the latest speculative execution attack that allows balaclava-wearing hackers to steal your sensitive information. You know it’s a real 0-day because it already has a domain, a logo, and this time, there’s a video explaining in simple terms anyone can understand why the sky is falling. The video uses ukuleles in the sound track, meaning it’s very well produced.

The Foreshadow attack relies on Intel’s Software Guard Extension (SGX) instructions that allow user code to allocate private regions of memory. These private regions of memory, or enclaves, were designed for VMs and DRM.

How Foreshadow Works

The Foreshadow attack utilizes speculative execution, a feature of modern CPUs most recently in the news thanks to the Meltdown and Spectre vulnerabilities. The Foreshadow attack reads the contents of memory protected by SGX, allowing an attacker to copy and read back private keys and other personal information. There is a second Foreshadow attack, called Foreshadow-NG, that is capable of reading anything inside a CPU’s L1 cache (effectively anything in memory with a little bit of work), and might also be used to read information stored in other virtual machines running on a third-party cloud. In the worst case scenario, running your own code on an AWS or Azure box could expose data that isn’t yours on the same AWS or Azure box. Additionally, countermeasures to Meltdown and Spectre attacks might be insufficient to protect from Foreshadown-NG

The researchers behind the Foreshadow attacks have talked with Intel, and the manufacturer has confirmed Foreshadow affects all SGX-enabled Skylake and Kaby Lake Core processors. Atom processors with SGX support remain unaffected. For the Foreshadow-NG attack, many more processors are affected, including second through eighth generation Core processors, and most Xeons. This is a significant percentage of all Intel CPUs currently deployed. Intel has released a security advisory detailing all the affected CPUs.

DDL-4 Is A Visually Pleasing Modular CPU

Today’s CPUs are so advanced that they might as well be indistinguishable from magic, right? Wrong! Fundamentally, modern CPUs can be understood logically like any other technology, it’s just that they’re very fast, very small, and very complex, which makes it hard to get to grips with their inner workings. We’ve come a long way from the dawn of the home computer in the 80s, but what if there was something even simpler again, built in such a way as to be easily understandable? Enter the DDL-4-CPU, courtesy of [Dave’s Dev Lab].

The DDL-4 is a project to build a modular 4-bit CPU using bitslice methods. This is where computations are broken down into simple operations with two-bit inputs, which are executed with basic logic gates like NOR and XOR. This is great for building a CPU from individual parts, as logic chips are readily available and their operation is readily understood. That’s what’s used here – good old 74-series logic, which you can find just about anywhere!

The build consists of a series of modules, each on its own colourful PCB and labeled on the silkscreen. These modules can then be configured and plugged together with edge connectors to build the CPU. The work builds upon [Dave]’s earlier work on the Mega-One-8-One, a recreation of the 74181 Arithmetic Logic Unit for educational purposes.

If you’re learning about computing in a bare-metal sense, projects like these that create CPUs from the ground up are a great way to get to grips with the basic concepts of computation. Once you’ve tried this, you could always graduate to building a 6502 in Minecraft.

High End PC Gets A Rustic Woodworking Piece Of Art For A Case

As [Matt] from [DIY Perks] was about to assemble a new PC, he decided to take a unique direction when it came to building a case. Despite the appearance of a woodworking piece with weird industrial radiators, there is actually a full-fledged, high-end PC hidden inside.

Those radiators are a pair of almost-the-biggest-you-can-buy heatsinks — one of which has been modified to fit the graphics card. Separating the graphics card’s stock cooling fan unit cut down significantly on noise and works with the stringent space requirements of the build. Those fans however keep other components on the card cool, so [Matt] cut pieces of copper plate to affix to these areas and joined them to the heatsink with a heat pipe, bent to shape. The elm wood case then began to take shape around the graphics card — cut into pieces to accommodate the heat pipes, and sealed with black tack to dampen the ‘coil whine’ of the GPU; it turns out the likely culprit are the MOSFETs, but close enough.

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