You Got Something On Your Processor Bus: The Joys Of Hacking ISA And PCI

January 6, 2021 by Maya Posch 32 Comments

Although the ability to expand a home computer with more RAM, storage and other features has been around for as long as home computers exist, it wasn’t until the IBM PC that the concept of a fully open and modular computer system became mainstream. Instead of being limited to a system configuration provided by the manufacturer and a few add-ons that really didn’t integrate well, the concept of expansion cards opened up whole industries as well as a big hobbyist market.

The first IBM PC had five 8-bit expansion slots that were connected directly to the 8088 CPU. With the IBM PC/AT these expansion slots became 16-bit courtesy of the 80286 CPU it was built around. These slots could be used for anything from graphics cards to networking, expanded memory or custom I/O. Though there was no distinct original name for this card edge interface, around the PC/AT era it got referred to as PC bus, as well as AT bus. The name Industry Standard Architecture (ISA) bus is a retronym created by PC clone makers.

With such openness came the ability to relatively easy and cheaply make your own cards for the ISA bus, and the subsequent and equally open PCI bus. To this day this openness allows for a vibrant ecosystem, whether one wishes to build a custom ISA or PCI soundcard, or add USB support to a 1981 IBM PC system.

But what does it take to get started with ISA or PCI expansion cards today? Continue reading “You Got Something On Your Processor Bus: The Joys Of Hacking ISA And PCI” →

Build An 8-bit CPU To Know “But How Do It Know?”

January 2, 2021 by Anool Mahidharia 14 Comments

Sometime around 2009, [J. Clark Scott] published a book aimed to demystify computers for everyone by walking through construction of an 8-bit CPU from scratch. The book had a catchy, but somewhat confusing title But How Do It Know?. The back story on the title goes something like this: Joe is a very nice fellow, but has always been a little slow. He goes into a store where a salesman is standing on a soapbox in front of a group of people. The salesman is pitching the miracle new invention, the Thermos bottle. He is saying, “It keeps hot food hot, and cold food cold….” Joe thinks about this a minute, amazed by this new invention that is able to make a decision about which of two different things it is supposed to do depending on what kind of food you put in it. He can’t contain his curiosity, he is jumping up and down, waving his arm in the air, saying “but, but, but, but…” Finally he blurts out his burning question “But how do it know?” Joe looked at what this Thermos bottle could do, and decided that it must be capable of sensing something about its contents, and then performing a heating or cooling operation accordingly. Joe’s concept of how the bottle worked was far more complicated than the truth. With that introductory opening, [J. Clark Scott] goes on to cover basic number theory, leading on to logic gates, and finally the 8-bit CPU.

[Patrick LeBoutillier] decided to build a hardware version of the CPU/computer as described in [John Clark Scott]’s book. In order to keep size and cost within reasonable bounds, he choose a hybrid construction using a combination of micro-controllers and SN74HC logic IC’s. When used as a companion project alongside reading the book, he hopes people can get their hands dirty and try it out for themselves. He has published a series of 14 videos covering construction of the CPU and the first Introductory video is embedded after the break below. For the micro-controller part of the project, he is using four Arduino Nanos, the code and install instructions for which are available at his Git repo. The Fritzing schematic, also available at the repo, might look a bit daunting at first look, but when you follow along his video series, it becomes easier. You can preview the first three chapters of the book at the “But How Do It Know?” website.

If FPGA’s are more of a thing for you, or you’d like to dip your feet learning FPGA, then [Patrick] has another series of 17 videos (embedded below) where he goes through the same process using a Digilent BASYS3 FPGA development board. These aren’t your only options — if you just want to understand how it works, without having to build the hardware, then check out the online, browser based implementation of the [Clark Scott] CPU.

If it seems the breadboard build of this 8-bit CPU looks complex, then this
Home Made 8-bit CPU Is A Wiry Blinky Build and a veritable rats nest of jumper wires.

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DIY 8-Bit Computer Knows All The Tricks

December 31, 2020 by Bryan Cockfield 12 Comments

Some projects are a rite of passage within their respected fields. For computer science, building one’s own computer from scratch is certainly among those projects. Of course, we’re not talking about buying components online and snapping together a modern x86 machine. We mean building something closer to a fully-programmable 8-bit computer from the ground up, like this one from [Federico] based on 74LS logic chips.

The computer was designed and built from scratch which is impressive enough, but [Federico] completed this project in about a month as well. It can be programmed manually through DIP switches or via a USB connection to another computer, and also includes an adjustable clock which can perform steps anywhere from 1 Hz to 32 kHz. Complete with a 1024 byte memory, a capable ALU, four seven-segment LEDs and (in the second version of the computer) a 2×16 LCD disply, this 8-bit computer has it all.

Not only is this a capable machine designed by someone who clearly knows his way around a logic chip, but [Federico] has also made the code and schematics available on his GitHub page. It’s worth a read even without building your own, but if you want to go that route without printing an enormous PCB you can always follow the breadboard route.

Thanks to [killergeek] for the tip!

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The X-PC, A Stylish Re-Imagining Of An Old Laptop

December 25, 2020 by Jenny List 24 Comments

There’s one certainty wherever schoolchildren come into contact with computers: the hardware will inevitably emerge worse for the encounter. The school laptops managed by [Neil Lambert] certainly suffered, losing keys and power supplies aplenty. Faced with a pile of broken machines, he came up with the X-PC, a stylish all-in-one desktop computer built around the innards of a laptop.

Inside a modern laptop there is surprisingly little in the way of parts, now that removable media drives are largely a thing of the past and once the battery has been removed from the equation. When the keyboard and trackpad are subtracted and replaced with USB equivalents the inner workings are reduced to a relatively compact motherboard and hard drive alongside the screen.

The screen is encased in a lasercut frame that also mounts the motherboard. It includes a lasercut cover that folds over the top in a living hinge to create an A-frame case that also holds the power supply. As an extra bonus the centre of the A provides handy storage for a keyboard.

Most of us will have encountered enough older laptops with broken parts to recognise the value in this build, seeing how it can transform junk into a useful machine. This certainly isn’t the first time we’ve seen someone try a similar build.

Extracting A Gate From AMD And Intel

December 1, 2020 by Matthew Carlson 16 Comments

The competition between Intel and AMD has been heating up in the last few years as Intel has released chips fabbed with their 14nm++ process and AMD has been using TMSC’s 7nm process. In the wake of the two semiconductor titans clashing, a debate between the merits of 14nm++ and 7nm has sprung up with some confusion about what those numbers actually measure. Not taking either number at their face value, [der8auer] decided to extract a transistor from both Intel’s and AMD’s latest offerings to try and shed some light.

Much of the confusion comes from the switch to the FinFET process. While older planar transistors could be thought of as largely 2d structures, FinFET’s are three dimensional. This means that the whole vertical fin can act as a gate, greatly reducing leakage. It is this fin or gate that [der8auer] is after. On each chip, a thin sliver from the L1 cache was chosen as caches tend to be fairly homogenous sections with transistors that are fairly indicative of the rest of the chip. Starting with a platinum gas intersecting with a focused ion beam on the surface of the chip, [der8auer] built a small deposit of platinum over several hours. This deposit protects the chip when he later cut it at an angle, forming a small lamella 100 micrometers long. In order for the lamella to be properly imaged by the scanning electron microscope, it needed to be even thinner (about 200 to 300nm).

Eventually, [der8auer] was ultimately able to measure the gate height, width, spacing, and other aspects of these two chips. The sheer amount of engineering and analysis that went into this project is remarkable and we love the deep dive into the actual gates that make up the processors we use. If you’re looking for a deep dive into the guts of a processor but perhaps at a more macro scale, why not learn about a forgotten Intel chip from the 1970s?

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Full 8-Bit Computer On Breadboards

November 23, 2020 by Bryan Cockfield 13 Comments

Getting into a big electronics project often involves the use of specialized tools, namely the use of some sort of soldering iron or other way to apply solder to often intricate, tiny, and heat-sensitive parts. While it’s best to learn to pick up this skill at some point, it’s not always necessary, even for big, complicated projects like [DerULF1]’s full 8-bit computer that he built entirely on breadboards.

For a fully featured 8-bit computer, this build goes deep into the details of how the computer works. The clock allows programs to be stepped through one cycle at a time, and even the memory can be individually accessed with a set of switches. There are plenty of other interesting features as well, such as using registers to access extra memory. It features an SPI port and PS/2 keyboard controller and also loads programs from an SD card.

The build was inspired by some of [Ben Eater]’s projects which famously focus on using logic gates and TTL chips to perform complex tasks, such as another breadboard computer which plays snake on a small display. It’s certainly a great way to learn about the inner function of computers, and better still that no soldering is required. But you may need a few extra breadboards.

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Adventures In Overclocking: Which Raspberry Pi 4 Flavor Is Fastest?

November 11, 2020 by Elliot Williams 56 Comments

There are three different versions of the Raspberry Pi 4 out on the market right now: the “normal” Pi 4 Model B, the Compute Module 4, and the just-released Raspberry Pi 400 computer-in-a-keyboard. They’re all riffing on the same tune, but there are enough differences among them that you might be richer for the choice.

The Pi 4B is easiest to integrate into projects, the CM4 is easiest to break out all the system’s features if you’re designing your own PCB, and the Pi 400 is seemingly aimed at the consumer market, but it has a dark secret: it’s an overclocking monster capable of running full-out at 2.15 GHz indefinitely in its stock configuration.

In retrospect, there were hints dropped everywhere. The system-on-a-chip that runs the show on the Model B is a Broadcom 2711ZPKFSB06B0T, while the SOC on the CM4 and Pi 400 is a 2711ZPKFSB06C0T. If you squint just right, you can make out the revision change from “B” to “C”. And in the CM4 datasheet, there’s a throwaway sentence about it running more efficiently than the Model B. And when I looked inside the Pi 400, there was this giant aluminum heat spreader attached to the SOC, presumably to keep it from overheating within the tight keyboard case. But there was one more clue: the Pi 400 comes clocked by default at 1.8 GHz, instead of 1.5 GHz for the other two, which are sold without a heat-sink.

Can the CM4 keep up with the Pi 400 with a little added aluminum? Will the newer siblings leave the Pi 4 Model B in the dust? Time to play a little overclocking!

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