cpu

111 Articles

Screen caps of upgraded BBC Micro, and OS 9 code

BBC Micro: A Retro Revamp With The 68008 Upgrade

October 1, 2024 by 2 Comments

The BBC Microcomputer, launched in the early 1980s, holds a special place in computing history. Designed for educational purposes, it introduced a generation to programming and technology. With its robust architecture and community-driven modifications, the BBC Micro remains a beloved project for retro computing enthusiasts. [Neil] from Retro4U has been delving into this classic machine, showcasing the fascinating process of repairing and upgrading his BBC Micro with a 68008 CPU upgrade.

Last week, [Neil] shared his progress, unveiling advancements in his repairs and upgrades. After tackling a troublesome beep issue, he successfully managed to get the BBC running with 32 KB of functional memory, allowing him to boot into BASIC. But he wasn’t stopping there. With ambitions set on installing the 68008 CPU, [Neil]’s journey continued.

The 68008 board offers significant enhancements, including multitasking capabilities with OS-9 and its own hard drive and floppy disk controller. However, [Neil] quickly encountered challenges; the board’s condition revealed the usual broken capacitors and a few other faulty components. After addressing these issues, [Neil] turned his attention to programming the necessary ROM for OS-9.

Looking to get your hands dirty? [Neil] has shared a PDF of the upgrade circuit diagram. You can also join the discussion with fellow enthusiasts on his Discord channel, linked in the video description.

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Mainframe Chip Has 360MB Of On-Chip Cache

September 8, 2024 by 29 Comments

It is hard to imagine what a mainframe or supercomputer can do when we all have what amounts to supercomputers on our desks. But if you look at something like IBM’s mainframe Telum chip, you’ll get some ideas. The Telum II has “only” eight cores, but they run at 5.5 GHz. Unimpressed? It also has 360 MB of on-chip cache and I/O and AI accelerators. A mainframe might use 32 of these chips, by the way.

[Clamchowder] explains in the post how the cache has a unique architecture. There are actually ten 36 MB L2 caches on the chip. There are eight caches, one for each core, plus one for the I/O accelerator, and another one that is uncommitted.

A typical CPU will have a shared L3 cache, but with so much L2 cache, IBM went a different direction. As [Clamchowder] explains, the chip reuses the L2 capacity to form a virtual L3 cache. Each cache has a saturation metric and when one cache gets full, some of its data goes to a less saturated cache block.

Remember the uncommitted cache block? It always has the lowest saturation metric so, typically, unless the same data happens to be in another cache, it gets moved to the spare block.

There’s more to it than that — read the original post for more details. You’ll even read speculation about how IBM managed a virtual L4 cache, across CPUs.

Cache has been a security bane lately on desktop CPUs. But done right, it is good for performance.

PCB data sheet of a custom 4-bit microcontroller

Building A Microcontroller From Scratch: The B4 Thinker Project

August 25, 2024 by No comments

[Marius Taciuc’s] latest endeavor, the B4 Thinker, offers a captivating glimpse into microcontroller architecture through a modular approach. This proof-of-concept project is meticulously documented, with a detailed, step-by-step guide to each component and its function.

Launched in 2014, the B4 Thinker project began with the ambitious goal of building a microcontroller from scratch. The resulting design features a modular CPU architecture, including a base motherboard that can be expanded with various functional modules, such as an 8-LED port card. This setup enables practical experimentation, such as writing simple assembly programs to control dynamic light patterns. Each instruction within this system requires four clock pulses to execute, and the modular design allows for ongoing development and troubleshooting.

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Custom Microcode Compiler, Made In Google Sheets

July 7, 2024 by 12 Comments

When homebrewing a CPU, one has to deal with microcode. Microcode is the low-level nuts and bolts of how, precisely, a CPU executes instructions (like opcodes) and performs functions such as updating the cycle counter or handling interrupt requests. To make this task easier, [Bob Alexander] created a microcode compiler built in Google Sheets to help with his own homebrew work, but it’s flexible and configurable enough to be useful to others, as well.

A CPU’s microcode usually lives in read-only memory, and writing the microcode is only one step in the journey. [Bob]’s tool compiles his microcode into files that can be burned into memory (multiple EEPROM chips, in [Bob]’s case) or used as a Verilog program in the case of implementing the CPU in an FPGA. It’s configurable enough to be adapted for other homebrew CPU projects, though one would of course have to re-write the microcode portion.

A read-only version of the spreadsheet makes for some fun browsing, and if it piques your interest enough to get a copy of your own complete with the compiler script, you can do that here. It uses Google Sheets, and writes the output files into one’s Google Drive.

This kind of low-level project really highlights the finer points of just how the hard work of digital computing gets done. A good example is the Gigatron which implemented a RISC CPU using only microcode, memory, and logic gates in the late 70s. We’ve even seen custom microcode used to aid complex debugging.

Keep Tabs On PC Use With Custom Analog Voltmeter

April 26, 2024 by 8 Comments

With the demands of modern computing, from video editing, streaming, and gaming, many of us will turn to a monitoring system of some point to keep tabs on CPU usage, temperatures, memory, and other physical states of our machines. Most are going to simply display on the screen but this data can be sent to external CPU monitors as well. This retro-styled monitor built on analog voltmeters does a great job of this and adds some flair to a modern workstation as well.

The build, known as bbMonitor, is based on the ESP32 platform which controls an array of voltmeters via PWM. The voltmeters have been modified with a percentage display to show things like CPU use percentage. Software running on the computers sends this data in real time to the ESP32 so the computer’s behavior can be viewed at a glance. Each voltmeter is also augmented with RGB LEDs that change color from green to red as use increases as well. The project’s creator, [Corebb], also notes that the gauges will bounce around if the computer is under heavy load but act more linearly when under constant load, also helping to keep an eye on computer status.

While the build does seem to rely on a Windows machine to run the software for export to the monitor, all of the code is open-sourced and available on the project’s GitHub page and could potentially be adapted for other operating systems. And, as far as the voltmeters themselves go, there have been similar projects in the past that use stepper motors as a CPU usage monitor instead.

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The 1970s Computer: A Slice Of Computing

March 6, 2024 by 44 Comments

What do the HP-1000 and the DEC VAX 11/730 have in common with the video games Tempest and Battlezone? More than you might think. All of those machines, along with many others from that time period, used AM2900-family bit slice CPUs.

The bit slice CPU was a very successful product that could only have existed in the 1970s. Today, if you need a computer system, there are many CPUs and even entire systems on a chip to choose from. You can also get many small board-level systems that would probably do anything you want. In the 1960s, you had no choices at all. You built circuit boards with gates on the using transistors, tubes, relays, or — maybe — small-scale IC gates. Then you wired the boards up.

It didn’t take a genius to realize that it would be great to offer people a CPU chip like you can get today. The problem is the semiconductor technology of the day wouldn’t allow it — at least, not with any significant amount of resources. For example, the Motorola MC14500B from 1977 was a one-bit microprocessor, and while that had its uses, it wasn’t for everyone or everything.

The Answer

The answer was to produce as much of a CPU as possible in a chip and make provisions to use multiple chips together to build the CPU. That’s exactly what AMD did with the AM2900 family. If you think about it, what is a CPU? Sure, there are variations, but at the core, there’s a place to store instructions, a place to store data, some way to pick instructions, and a way to operate on data (like an ALU — arithmetic logic unit). Instructions move data from one place to another and set the state of things like I/O devices, ALU operations, and the like.

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How To Build Your Own 16-Bit System-on-Spreadsheet

January 30, 2024 by 17 Comments

Back in the hazy days of the  early home computers, many of us would rejoice at running our first BASIC applications, some of us even built our own 8-bit system from a handful of ICs and felt elated the moment the connected LEDs, screen or other output device would show signs of life. It is this kind of excitement that [Inkbox] has managed to bring to the bane of every office worker: spreadsheet programs like Excel. How, you may ask? Why, by implementing a completely functional 16-bit system with 16 general purpose registers, 128 kB of RAM and a 128×128 pixel color display, all inside an Excel spreadsheet, making it conceivably the world’s first System-on-Spreadsheet (SoS).

Perhaps the most tantalizing aspect of this approach is that it provides a very good visual way to indicate what is happening inside the system using color codes and clearly segregated and marked functional elements. Not only can it be programmed manually, but [Inkbox] also created an assembler for the CPU’s ISA – called Excel-ASM16 – all of which is available from the ExcelCPU GitHub project page. The ASM is assembled into a ROM.xlsx file that can then be run by the CPU.xlsx file by triggering the Read ROM button. After this you are confronted with the realization that although it all works, it’s also incredibly slow, at about 2-3 Hz.

Still, with all the elegance of an IMSAI 8080 front panel, we cannot help but give full points for this achievement. Plus it gives many of us something to do during those exceedingly dull meetings where only serious applications like office suites are allowed.

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