forth

31 Articles

Bit-Serial CPU: Ultra-Tiny VHDL-Based CPU With Forth Interpreter

February 24, 2024 by 11 Comments

Soft cores for FPGAs come in many different flavors, covering a wide range of applications. The Bit-Serial CPU (bcpu) soft core presented by [Richard James Howe] is interesting for taking up just about the most minimal amount of resources (23 slices, 76 LUTs) while providing the means to run a Forth-based (eForth dialect) interpreter. To this CPU core a UART can be added (92 LUTs), as well as other peripherals.

As [Richard] states, the entire core with UART fits in 73 slices (220 LUTs) on a Spartan 6, while requiring a single port BRAM (block RAM). It features a 16-bit accumulator and lacks features such as interrupts, byte addressability and function calls, but those are not required to run the eForth interpreter. The main purpose of this soft core (other than the challenge) is to have a UART-programmable core that can be slotted in any FPGA design. For more serious requirements [Richard] also has the H2 SoC, which can run full-fat FORTH.

Continue reading “Bit-Serial CPU: Ultra-Tiny VHDL-Based CPU With Forth Interpreter” →

Recreating The Jupiter ACE

January 7, 2024 by 25 Comments

What looks like a Sinclair ZX81 but runs Forth? If you said a Jupiter ACE, you get a gold star. These are rare because ordinary people in 1982 didn’t want Forth, so only about 5,000 of the devices were sold. [Cees Meijer] assumes they are unaffordable, so he built a replica and shows you how you can, too. [Scott Baker] built one recently; you can see his video below.

The resemblance to the Sinclair computer wasn’t just a coincidence. Richard Altwasser and Steven Vickers were behind the computer, and both had worked for Sinclair previously. In addition to being famous for using Forth, the machine initially had a badly manufactured case and an unreliable keyboard. A later version tried to correct these issues, but there were fewer than 1,000 made. [Cees’] replica used a design from [Grant Searle] with some modifications.

We liked the realistic look of the 3D printed keyboard. The keyboard uses white plastic with raised letters. A quick black spray paint followed by sanding gives the appearance of black keys with white printed text.

Overall, this is a good-looking build of a computer you probably won’t see in person. We wish Forth had caught on in the early PC world, but it didn’t. [Grant] was prolific with replica computers, and [Cees] isn’t the only one who used that work as a starting point for their own projects. If you want real old-school Forth, you have to go back a few more years.

Continue reading “Recreating The Jupiter ACE” →

Tiny Forth Could Be The Smallest

November 6, 2023 by 28 Comments

When you think of a programming language, you probably think of a hefty compiler or interpreter. Maybe its on a bunch of floppies, a CD, or even an EEPROM. But what about a language that fits in a single disk sector? A language like that would — in theory — be used to help bootstrap a computer system and that was the idea behind Sector Forth and, later, Sector Lisp. However, there’s a new game in town: milliForth, which claims to be the smallest ever at 422 380 bytes.

Why would you want such a thing? Well, first of all, why not? Even as a form of code golf, packing a functioning language into a tiny space seems interesting. However, you could also presumably use something like this to boot a small system or on a system with limited storage.

Continue reading “Tiny Forth Could Be The Smallest” →

Learn Forth On The Commodore VIC-20

November 3, 2023 by 14 Comments

Although BASIC was most commonly used on home computers like the Commodore VIC-20, it was possible to write programs in other languages, such as Forth. Conveniently, all it took to set up a Forth development system was inserting the cartridge into the VIC-20 and powering it on, with the VIC-FORTH cartridge by [Tom Zimmer] being a popular choice for the Commodore VIC-20. In a recent video, the [My Developer Thoughts] YouTube channel covers Forth development using this cartridge.

In addition to the video tutorial, the original VIC-FORTH Instruction Manual is also available, together with the 1541 disk image. In an upcoming video, the Commodore 64 version of the cartridge will also be covered, which is called 64Forth, and which is also readily available to tinker with. For those interested in learning more about [Tom Zimmer] and his Forth-related work, a 2010 interview could be interesting. This covers the other platforms which he developed an implementation for.

As for why Forth might be interesting to developers and users, this comes mostly down to the much lower overhead of Forth compared to BASIC, while avoiding the pitfalls of ASM and resource-intensive nature of developing in C, as the entire Forth development system (compiler, editor, etc.) comfortably fits in the limited memory of the average 8-bit home computer.

(Thanks to [Stephen Walters] for the tip)

Continue reading “Learn Forth On The Commodore VIC-20” →

A NOR Gate For An ALU?

April 5, 2023 by 18 Comments

If you know anything about he design of a CPU, you’ll probably be able to identify that a critical component of all CPUs is the Arithmetic Logic Unit, or ALU. This is a collection of gates that can do a selection of binary operations, and which depending on the capabilities of the computer, can be a complex component. It’s a surprise then to find that a working CPU can be made with just a single NOR gate — which is what is at the heart of [Dennis Kuschel]’s My4th single board discrete logic computer. It’s the latest in a series of machines from him using the NOR ALU technique, and it replaces hardware complexity with extra software to perform complex operations.

Aside from a refreshingly simple and understandable circuit, it has 32k of RAM and a 32k EPROM, of which about 9k is microcode and the rest program. It’s called My4th because it has a Forth interpreter on board, and it has I2C and digital I/O as well as a serial port for its console.

This will never be a fast computer, but the fact that it computes at all is ts charm. In 2023 there are very few machines about that can be understood in their entirety, so this one is rather special even if it’s not the first 1-bit ALU we’ve seen.

Thanks [Ken Boak] for the tip.

Forth Cracks RISC-V

January 8, 2023 by 48 Comments

Over the decades there have been many programming languages, some of which have flowered briefly, and others that have stuck around despite newer, better, and faster competition. Few languages embody this last group more than FORTH, over five decades old and still cropping up wherever a simple, elegant, fast, and compact stack-based programming language fits the bill. [Alexander Williams] has now taken it somewhere new, with a FORTH in RISC-V assembly which runs on the GD32 series of microcontrollers that are RISC-V lookalikes of the popular STM32 ARM parts.

We have to admit to last having used FORTH on an 8-bit home computer in the 1980s, aside from a moment’s idle play on discovering that the Open Firmware on Apple computers is a FORTH interpreter. Thus we’re intrigued by this implementation, but not from a position of FORTH expertise. We’d expect such an efficient language to be extremely quick though, so it’s definitely something to keep an eye on for when a suitable dev board comes our way. If it interests you, take a look at the GitHub repository.

HP-41C, The Forth Edition

October 21, 2022 by 38 Comments

If you have an HP-41 — arguably the best calculator ever made, you might not have noticed that there’s a version of Forth for it. The code was written a while back in assembly and will work on anything that actually emulates the device properly, such as a SwissMicros DM41X. [Calculator Clique] shows you how it works in a recent video that you can watch below.

The original code dates back to 1984, but some recent detective work by [Angel Margin] has the code running again. If you know about synthetic programming on the 41C and the oddities of its internal architecture, you can’t help but be impressed.

Of course, Forth is meant to be easy to port over, but if you read about some of the architectural challenges, you start to realize this could be one of the more difficult implementations you’ve ever seen. Don’t forget you have what is, by today’s standards, an extremely limited amount of resources.

That being said, calling the HP41C a calculator is almost a crime. It is really a tiny computer hiding inside a calculator case. Then again, the best calculators always are.

We wonder if the code would run on an emulated 41C? Were you part of the TI calculator gang? No problem.

Continue reading “HP-41C, The Forth Edition” →