Dis-Integrated 6502 Running Programs; Acting Like Computer

[Eric Schlaepfer] tends to turn up to Maker Faire with projects you simply don’t want to miss. This year is no different. Twelve months ago we delighted in seeing his 6502 processor built from an enormous reel of discrete MOSFETs. At the time it was freshly built and running random code to happily blink the LEDs reflecting activity in the registers. This year he’s given that blinking meaning and is running real programs on his Monster 6502 processor.

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Introducing The MENSCH Microcomputer

A few weeks ago, I was browsing Tindie on one of my daily trawls for something interesting to write about. I came across something I hadn’t seen before. The Mensch Microcomputer is a product from Western Design Center (WDC) that puts a microcontroller based on the 65xx core on a small breakout board.

I’ve played around with some of WDC’s tools and toys before, back when the sent me a few dev boards to review. They’re cool, and I have considered building a little breakout board for this weird cross between a microcontroller and a system on a chip. Life gets in the way, and that project sat on the shelf. The Mensch, however, was cheap and well into impulse purchase territory. After buying one, one of the VPs at WDC asked if I’d be interested in doing another review on their latest bit of hardware. Sure. I got this.

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A 6502 Retrocomputer In A Very Tidy Package

One of the designers whose work we see constantly in the world of retrocomputing is [Grant Searle], whose work on minimal chip count microcomputers has spawned a host of implementations across several processor families.

Often a retrocomputer is by necessity quite large, as an inevitable consequence of having integrated circuits in the period-correct dual-in-line packages with 0.1″ spaced pins. Back in the day there were few micros whose PCBs were smaller than a Eurocard (100 mm x 160 mm, 4″ x 6.3″), and many boasted PCBs much larger.

[Mark Feldman] though has taken a [Grant Searle] 6502 design and fitted it into a much smaller footprint through ingenious use of two stacked Perf+ prototyping boards. This is a stripboard product that features horizontal traces on one side and vertical on the other, which lends itself to compactness. Continue reading “A 6502 Retrocomputer In A Very Tidy Package”

An Intel 8085 Microprocessor Trainer

The Intel 8085 microprocessor was introduced 40 years back, and along with its contemporaries — the Z80 and the 6502 — is pretty much a dinosaur in terms of microprocessor history. But that doesn’t stop it from still being included in the syllabus for computer engineering students in many parts of the world. The reason why a 40 year old microprocessor is still covered in computer architecture text books instead of computer history is a bit convoluted. But there’s a whole industry that thrives on the requirements of college laboratories and students requiring “8085 Microprocessor Training Kits”. [TisteAndii] just finished college in Nigeria, where these kits are not locally built and need to be imported, usually costing well over a 100 dollars.

Which is why his final year project was a low cost Intel 8085 Microprocessor Trainer. It’s a minimalist design with some basic read/write memory, program execution and register inspection, with no provision for single stepping or interrupts yet. The monitor program isn’t loaded in an EEPROM. Instead, a PIC18 is used and connected to the 8085 address, data and control pins. This makes it easier to write a monitor program in C instead of assembly. And allows use of a 1.8″ LCD with SPI interface instead of the more usual 7-segment displays used for these kind of kits. [TisteAndii] built a 6×4 keyboard for input, but couldn’t solve debounce issues and finally settled on a 5×4 membrane keypad.

Being a rookie, he ended up with a major flaw in his board layout — he missed connecting the SRAM and the PPI devices to the data bus. A bunch of jumper links seemed to solve the issue, but it wasn’t perfect. This, and a few other problems gave him a lot of grief, but towards the end, it all worked, almost. Most importantly, his BoM cost of about $35 makes it significantly cheaper compared to the commercial units available in Nigeria.

While some hackers may consider this a trivial project, it solves a local problem and we hope the next iteration of the design improves the kit and makes it more accessible.

A Linux Exploit That Uses 6502 Code

With ubiquitous desktop computing now several decades old, anyone creating an operating system distribution now faces a backwards compatibility problem. Each upgrade brings its own set of new features, but it must maintain compatibility with the features of the previous versions or risk alienating users. If you are a critic of Microsoft products for their bloat, this is one of the factors behind that particular issue.

As well as a problem of compatibility, this extra software overhead creates one of security. A piece of code descended from a DOS word processor of the 1980s for example was not originally created with any idea that it might one day be hiding in a library on a machine visible to the entire world by the Internet. Our subject today is a good example, just such a vulnerability hiding in an old piece of code whose purpose is to maintain an obscure piece of backward compatibility. [Chris Evans] has demonstrated a vulnerability in an Ubuntu version by playing an NES music file that contains exploit code emulated by the player on a virtual 6502 processor.

The NES Sound Format is a music file standard that packages Nintendo game music for playback. It contains a scripting language, and it is this that is used to trigger the vulnerability. When you open an NSF file on the affected Ubuntu system it finds its way via your music player and the gstreamer multimedia framework to libgstnsf.so, a gstreamer plugin for playing NSF files.

Rather unbelievably, his plugin works by emulating a real 6502 as found in a NES to derive the musical output, and it is somewhere here that the vulnerability exists. So not only do we have layer upon layer of backward compatibility to play an obscure music file format, there is also a software emulation of some 8-bit silicon from the 1970s. [Chris] comments “Is that cool or what?“, and while we agree that a 6502 emulator buried in a modern distro is cool, we can’t help thinking something’s been lost along the way.

A proof-of-concept is provided for Ubuntu 12.04. It’s an older version, but he points out that while he thinks the most recent releases should not contain exactly the same vulnerability, it certainly exists in more than one still-supported version. There’s also a worrying twist in that due to the vagaries of Ubuntu’s file manager it auto-opens when its folder is accessed from the GUI. The year 2000 called, they want their auto-opening Windows ME worms back.

Sadly we suspect the 6502 lurking in this music player can’t be put to more general-purpose use. If you manage it, please do share it with us! But if emulated 6502s are your thing, take a look at this 150MHz 6502 co-processor for an Acorn BBC Micro that someone made using a Raspberry Pi.

[via r/hacking]

6502 image, Dirk Oppelt, (CC BY-SA 3.0) via Wikimedia Commons.

Making A Cassette Mass Storage Interface

If you are of the generation who were lucky enough to use the first 8-bit home computers in your youth, you will be familiar with their use of cassette tapes as mass storage. Serial data would be converted to a sequence of tones which could then be recorded using a standard domestic cassette recorder, this recording could then be played back into the machine’s decoder and loaded into memory as a complete piece of software. Larger programs could take a while to load, but though it was rather clunky it was a masterful piece of making the best of what was at hand.

[Mike Kohn] was working with some microcontroller infra-red communication projects when he saw that the same techniques could be used to produce a tape interface like those on the home computers of old.

Over the years he has returned to the project a couple of times, and his original Atmel processor has been supplanted by a W65C265SXB development board based on the 16-bit derivative of the 6502. This made generating the tones as straightforward using his processor’s built-in tone generator, but decoding still presented a challenge. His earlier attempts used an LM2917 frequency to voltage converter to decode tones to logic levels, but on further consideration he decided to move to the LM567 tone decoder. This chip is designed specifically for an on-off logic output rather than the 2917’s analogue voltage output.

His recording device was originally a hi-fi separate cassette deck after experimenting with microcassettes, but eventually he used a data recorder designed for a Radio Shack TRS-80. All his code can be found in his GitHub repository.

It’s probably true to say that [Mike] has made a better cassette interface than the one you could have found on your home computer back in the day. We’ve featured a few data cassette hacks over the years, including this Commodore tape deck with an LED counter, and a tape deck emulator capable of holding an entire software archive.

Hackaday Prize Entry: Dodo 6502 Game System

If you are a gamer of A Certain Age, it’s probable that you retain a soft spot for 8-bit computers and consoles of your youth. For a time when addictive gameplay came through the most minimal of graphics, and when gaming audio was the harshest of square waves rather than immersive soundscapes.

Does the previous paragraph sound familiar? Then we may just have the device for you. The Dodo is a handheld console that harks back to that era with a 6502 processor and a 128×64 pixel OLED screen. Games are loaded from plug-in EEPROM cartridges, and sounds are suitably period-digital square wave tones. It’s the brainchild of [Peter Noyes], and he says he will consider it complete when it sports a game fun enough to entertain his 4-year-old.

The prototype Dodo is a handheld form-factor made from two stacked PCBs. The upper one has the display and buttons while the lower has the classic 6502 and associated chipset in through-hole DIP format. A Game Boy Micro it ain’t, but miniaturization is not the name of the game with these consoles. Best of all though, all the console’s resources are available in a GitHub repository, so you can all have a play too.

The 6502 has featured in a huge number of projects here on Hackaday over the years. Now it’s turned up in the Hackaday Prize.