Hands up if you’ve ever used a machine running CP/M. That’s likely these days to only produce an answer from owners of retrocomputers. What was once one of the premier microcomputer operating systems is now an esoteric OS, a piece of abandonware released as open source by the successor company of its developer.
In the 1970s you’d have seen CP/M on a high-end office wordprocessor, and in the 1980s some of the better-specified home computers could run it. And now? Aside from those retrocomputers, how about running CP/M on an ESP8266? From multi-thousand-dollar business system to two-dollar module in four decades, that’s technological progress.
[Matseng] has CP/M 2.2 running in a Z80 emulator on an ESP8266. It gives CP/M 64K of RAM, a generous collection of fifteen 250K floppy drives, and a serial port for communication. Unfortunately it doesn’t have space for the ESP’s party piece: wireless networking, but he’s working on that one too. If you don’t mind only 36K of RAM and one less floppy, that is. All the code can be found on a GitHub repository, so if you fancy a 1970s business desktop computer the size of a postage stamp, you can have a go too.
There’s something gloriously barmy about running a 1970s OS on a two-dollar microcontroller, but if you have to ask why then maybe you just don’t understand. You don’t have to have an ESP8266 though, if you want you can run a bare-metal CP/M on a Raspberry Pi.
At its heart is the EduCIAA NXP Board, a Dual Core (M4 & M0) 32-bit microcontroller, based on the NXP LPC4337. It’s an Argentinan-designed microcontroller board, born from an Argentinian academic and industry joint venture. [telmomoya] took advantage of the multicore architecture by running the ZX Spectrum emulator on M4 core and generating the VGA signals with M0 core. This guarantees that the VGA generation, which is rather time-sensitive, remains isolated from emulation and any task running on other core. The VGA sync is via polling and using DMA GPIO the RGB signals can be up to 256 colors. To store the 48 kb VGA frames one AHB32 and one AHB16 memory IC are used.
On the software side, [telmomoya] adopted Aspectrum, a ZX Spectrum Emulator fully written in C, modified to his needs. Overall, the project faced many challenges and issues, like COLOR VGA generation (with GPIO DMA), TFT SPI low fps, Inter Process Communications and bus sharing.
Can you try to name all the games in the demonstration video?
Emulators are a great way to reminisce about games and software from yesteryear. [Jorj Bauer] found himself doing just that back in 2002, when they decided to boot up Three Mile Island for the Apple II. It played well enough, but for some reason, crashed instantly if you happened to press the ‘7’ key. This was a problem — the game takes hours to play, and ‘7’ is the key for saving and restoring your progress. In 2002, [Jorj] was content to put up with this. But finally, enough was enough – [Jorj] set out to fix the bug in Three Mile Island once and for all.
The project is written up in three parts — the history of how [Jorj] came to play Three Mile Island and learn about Apple IIs in the first place, the problem with the game, and finally the approach to finding a solution. After first discovering the problem, [Jorj] searched online to see if it was just a bad disk image causing the problem. But every copy they found was the same. There was nothing left for it to be but problem in the binary.
Emulation is a difficult thing to do, particularly when you’re trying to emulate a complex platform like a game console, with little to no public documentation available. Often, you’ll have to figure things out by brute force and dumb luck, and from time to time everything will come unstuck when a random piece of software throws up an edge case that brings everything screeching to a halt.
The Classic NES series was a handful of Nintendo Entertainment System games ported to the Game Boy Advance in the early 2000s. What makes them unique is a series of deliberately obtuse programming decisions that make them operate very differently from other titles. These tricks utilize advanced knowledge of the way the Game Boy Advance hardware operates and appear to have been used to make the games difficult to copy or emulate.
The games use a variety of techniques to confuse and bamboozle — from “mirrored memory” techniques that exploit addressing anomalies, to putting executable code in video RAM and writing to the audio buffers in unusual manners.
Even more confusingly, these techniques only appear to have been used in the Classic NES series of games, and not other Game Boy Advance titles. It’s not obvious why Nintendo went to special effort to protect these ports over other titles; perhaps the techniques used were for other reasons than just an attempt at copy protection. Speculate amongst yourselves in the comments.
A well-designed phone case will protect your phone from everyday bumps with only as much style flair as you’d like. While protection is usually the only real function of a case, some designs — like [Gabbelago]’s Emucase — add specific utility that you might not have known you needed.
Contrary to most cases, the Emucase fits over your phone’s screen, and the resulting facelift emulates the appearance of a Game Boy for easier — you guessed it — Game Boy emulation play on your smartphone.
Cannibalizing a USB SNES gamepad for its buttons and rubber contact pads, Gabbelago then threaded some wire through the contacts, securing it with copper tape and glue; this provides a measurable level of capacitance to register on the touchscreen. Using heat to bend the sides of the 3D printed case so it can attach to the phone is probably the trickiest part of this cool project. Check out his build instructions for any pointers you need.
The Apple II was one of the first home computers. Designed by Steve “Woz” Wozniak, it used the MOS technologies 6502 processor, an 8-bit processor running at about 1 MHz. [Maxstaunch] wrote his bachelor thesis about emulating the 6502 in software on an AVR1284 and came up with a handheld prototype Apple II with screen and keyboard.
Originally, [maxstrauch] wanted to build an NES, which uses the same 6502 processor, but he calculated the NES’s Picture Processing Unit would be too complicated for the AVR, so he started on emulating the Apple II instead. It’s not quite there – it can only reference 12K of memory instead of the 64K on the original, so hi-res graphic mode, and therefore, many games, won’t work, but lo-res mode works as well as BASIC (both Integer BASIC and Applesoft BASIC.)
[Maxstrauch] details the 6502 in his thesis and, in a separate document, he gives an overview of the project. A third document has the schematic he used to build his emulator. His thesis goes into great detail about the 6502 and how he maps it to the AVR microcontroller. The build itself is pretty impressive, too. Done on veroboard, the build has a display, keyboard and a small speaker as well as a micro SD card for reading and storing data. For more 6502 projects, check out the Dis-Integrated 6502 and also, this guide to building a homebrew 6502.
[GreatScott] bought a Game Boy case. Normally, you’d assume you wanted this to repair a damaged Game Boy, but in this case [GreatScott] used a Pi Zero and some 3D printing to build a game system into the tiny box. You can see some videos, below.
Two interesting parts of the project are the source of the LCD display (a rearview camera screen) and the selection of batteries. Lithium ion batteries are all the rage. But if you watch the news, you know there are some safety issues with using the batteries, especially if you use them improperly. [GreatScott] decided to go with nickel metal hydride cells which still need a protection circuit, but are typically less of a danger than the newer technology cells.