Here’s How To Build A Tiny Compiler From Scratch

May 21, 2023 by Donald Papp 27 Comments

Believe it or not, building a tiny compiler from scratch can be as fun as it is accessible. [James Smith] demonstrates by making a tiny compiler for an extremely simple programming language, and showing off a hello world.

Here’s what happens with a compiler: human-written code gets compiled into low-level machine code, creating a natively-executable result for a particular processor. [James]’ compiler — created from scratch — makes native x64 Linux ELF binary executables with no dependencies, an experience [James] found both educational and enjoyable. The GitHub repository linked below has everything one needs, but [James] also wrote a book, From Source Code to Machine Code, which he offers for sale to anyone who wants to step through the nitty-gritty.

The (very tiny) compiler is on GitHub as The Pretty Laughable Programming Language. It’s tiny, the only data types are integers and pointers, and all it can do is make Linux syscalls — but it’s sufficient to make a program with. Here’s what the code for “Hello world!” looks like before being fed into the compiler:

; the write() syscall: ; ssize_t write(int fd, const void *buf, size_t count); (syscall 1 1 "Hello world!\n" 13) 0

Working at such a low level can be rewarding, but back in the day the first computers actually relied on humans to be compilers. Operators would work with pencil and paper to convert programs into machine code, and you can get a taste of that with a project that re-creates what it was like to program a computer using just a few buttons as inputs.

An Entire RISC-V Operating System In 2000 Lines

May 18, 2023 by Bryan Cockfield 34 Comments

While Microsoft and Apple don’t release the source code for their operating systems, a good estimate is that it takes around 50 million lines of code to run these software behemoths. The Linux kernel alone holds around 30 million lines, with systemd containing over one million lines on its own, which doesn’t include estimates for the desktop environment or other parts of a standard installation. But millions of lines of code, or even hundreds of thousands, aren’t necessary for building a fully functioning operating system. This one sets up a complete OS in exactly 2000 lines of code.

Called egos-2000, short for Earth and Grass Operating System, the diminutive operating system is written for RISC-V computers and while it does contain most of the tools we would recognize in an OS, it was built specifically for computer science students by PhD candidate Yunhao Zhang. The slimmed-down operating system makes it possible for students to easily read and understand every feature of an operating system without it becoming too overwhelming, and can be easily used and modified to experiment with. The name itself comes from its design principles, where parts of the operating system that interact with hardware directly are part of the “Earth” layer and parts that don’t depend on hardware being placed in the “Grass” layer, with applications taking up a third layer.

The OS is available on this GitHub page under an MIT license and works on real RISC-V hardware as well as within various emulators. Building a complete operating system in so few lines of code is an impressive feat, and making it comprehensive enough to teach students with goes well beyond that accomplishment as well. Often when concepts in computer science are reduced to their bare minimum components, we end up with completely illegible (but interesting) experiments like this programming language instead.

Turning Old Kindles Into AI Powered Picture Frames

May 15, 2023 by Tom Nardi 4 Comments

While we tend to think of Amazon’s e-paper Kindles as more or less single-purpose devices (which to be fair, is how they’re advertised), there’s actually a full-featured Linux computer running behind that simple interface, just waiting to be put to work. Given how cheap you can get old Kindles on the second hand market, this has always struck us as something of a wasted opportunity.

This is why we love to see projects like Kindlefusion from [Diggedypomme]. It turns the Kindle into a picture frame to show off the latest in machine learning art thanks to Stable Diffusion. Just connect your browser to the web-based control interface running on the Kindle, give it a prompt, and away it goes. There are also functions to recall previously generated images, and if you’re connecting from a mobile device, support for creating images from voice prompts.

You can find cheap older Kindles on eBay.

All you need is a Kindle that can be jailbroken, though technically the software has only been tested against older third and fourth-generation hardware. From there you install a few required packages as listed in the project documentation, including Python 3. Then you just move the Kindlefusion package over either via USB or SSH, and do a little final housekeeping before starting it up and letting it take over the Kindle’s normal UI.

Given the somewhat niche nature of Kindle hacking, we’re particularly glad to see that [Diggedypomme] went through the trouble of explaining the nuances of getting the e-reader ready to run your own code. While it’s not difficult to do, there are plenty of pitfalls if you’ve never done it before, so a concise guide is a nice thing to have. Unfortunately, it seems like Amazon has recently gone on the offensive, with firmware updates blocking the exploits the community was using for jailbreaking on all but the older models that are no longer officially supported.

While it’s a shame you can’t just pick up a new Kindle and start hacking (at least, for now), there are still millions of older devices floating around that could be put to good use. Hopefully, projects like this can help inspire others to pick one up and start experimenting with what’s possible.

Continue reading “Turning Old Kindles Into AI Powered Picture Frames” →

A DR-DOS console showing the IDLE command

Missing DR-DOS Power Management Source Code Found In Patent

May 14, 2023 by Robin Kearey 20 Comments

Modern processors come with all kinds of power management features, which you don’t typically notice as a user until you start a heavy program and hear the CPU fan spin up. Back in the early 1990s however, power management was largely unheard of, meaning that a CPU with nothing to do would run through an idle loop that dissipated about as much power as a real computing task. [Michal Necasek] noticed this while experimenting with DR-DOS 6.0 in a virtual machine – his laptop fan would start running on full blast whenever he opened the VM. His search for a solution to this annoyance led him down a fascinating journey into the intricacies of DOS power management.

As it turned out, DR-DOS 6.0 does have functionality built in for putting the CPU in power saving mode when it’s idle. This feature is not complete, however: Digital Research required each computer manufacturer to develop an IDLE driver customized to their specific hardware platform in order to enable power management. Sadly, no manufacturer ever bothered to do so, leaving [Michal] with no option other than writing a driver himself. While there was some documentation available, it didn’t include any example code or sufficient detail to write a driver from scratch.

What it did include was a reference to U.S. Patent No. 5,355,501. Normally this sort of information is of interest only to those planning to sell a competing system, but this specific patent happens to include dozens of pages of well-documented but poorly-scanned x86 assembly code, including source code for a basic IDLE86.SYS driver. As [Michal] wasn’t looking forward to chasing bugs caused by OCR errors, he simply copied the source code by hand, then ran it through an assembler. The end result was a working IDLE driver, which is now available for download from his website.

[Michal]’s blog post also includes lots of details on early power saving implementations, including all the DOS interrupt calls involved in the process. Patents might seem boring in contrast, but they sometimes contain surprising amounts of usable information. You might find enough details to reverse-engineer a wireless protocol, or even to help track down an obscure instrument’s original designer.

WordStar Reborn

May 9, 2023 by Al Williams 48 Comments

Wordstar was the word processor that helped sell the personal computer. At one time, it was ubiquitous, and many authors had a hard time giving it up. Some, like George R. R. Martin, apparently are still refusing to give it up. But most of us have moved on. Thanks to an open-source clone, WordTsar, you may not have to. This is a modern interpretation of our old friend.

Programmers that write were especially fond of WordStar since it had a non-document mode and was often the best text editor you had available for writing code. Being able to do your documentation without switching brain gears is useful, too. Touch typists love the efficiency of easy control of things without resorting to cursor keys or a mouse — the same thing vi and emacs fans enjoy but in a different way.

The software runs on multiple platforms and has some new features. Installation on Linux is easy because it is packaged in an AppImage file. Of course, you can also fire up your best CP/M machine, replica, or emulation and run the real WordStar, but — honestly — WordTsar seems more practical if you wanted to go back to using this kind of wordprocessor or editor for everyday use.

Of course, some word processors were actual hardware. If you want some cheap CP/M hardware, that’s easy enough, too.

A Literate Assembly Language

May 8, 2023 by Al Williams 80 Comments

A recent edition of [Babbage’s] The Chip Letter discusses the obscurity of assembly language. He points out, and I think correctly, that assembly language is more often read than written, yet nearly all of them are hampered by obscurity left over from the days when punched cards had 80 columns and a six-letter symbol was all you could manage in the limited memory space of the computer. For example, without looking it up, what does the ARM instruction FJCVTZS do? The instruction’s full name is Floating-point Javascript Convert to Signed Fixed-point Rounding Towards Zero. Not super helpful.

But it did occur to me that nothing is stopping you from writing a literate assembler that is made to be easier to read. First, most C compilers will accept some sort of asm statement, and you could probably manage that with compile-time string construction and macros. However, I think there is a better possibility.

Reuse, Recycle

Since I sometimes develop new CPU architectures, I have a universal cross assembler that is, honestly, an ugly hack, but it works quite well. I’ve talked about it before, but if you don’t want to read the whole post about it, it uses some simple tricks to convert standard-looking assembly language formats into C code that is then compiled. Executing the resulting program outputs the desired machine language into a desired file format. It is very easy to set up, and in the middle, there’s a nice C program that emits machine code. It is not much more readable than the raw assembly, but you shouldn’t have to see it. But what if we started the process there and made the format readable?

At the heart of the system is a C program that lives in soloasm.c. It handles command line options and output file generation. It calls an external function, genasm with a single integer argument. When that argument is set to 1, it indicates the assembler is in its first pass, and you only need to fill in label values with real numbers. If the pass is a 2, it means actually fill in the array that holds the code.

That array is defined in the __solo_info instruction (soloasm.h). It includes the size of the memory, a pointer to the code, the processor’s word size, the beginning and end addresses, and an error flag. Normally, the system converts your assembly language input into a bunch of function calls it writes inside the genasm function. But in this case, I want to reuse soloasm.c to create a literate assembly language. Continue reading “A Literate Assembly Language” →

PC Classics, Right In Your Browser With EmuOS

May 6, 2023 by Donald Papp 11 Comments

[Emupedia]’s work to preserve computer history by way of making classic and abandoned games and software as accessible as possible is being done in a handy way: right in your browser with EmuOS.

A few moments of BIOS startup kicks off EmuOS right in a browser window.

Doing things this way has powerful “Just Works” energy. Visit that link in a modern browser and in no time at all you’ll be looking at a Windows 95 (or Windows 98, or Windows ME) desktop, filled with a ton of shortcuts to pre-installed and ready-to-run classic software. Heck, you can even keep it simple and be playing the original Microsoft Solitaire in no time flat. There is also a whole ton of DOS software waiting to be fired up, just double-click the DOSBox icon, and browse a huge list. The project is still in development, so not everything works, but the stuff that does is awfully slick.

Here’s some additional background that goes into more detail about the project and its capabilities, but if you’d prefer to just click around to explore, here’s the main link again (and here’s a list of mirrors.)

If OS emulation is your thing, don’t miss emulating the IBM PC on an ESP32 microcontroller. And if you’re more into lesser-known vintage operating systems, how about re-inventing PalmOS to run on x86 architecture?