assembly

101 Articles

Unexpectedly Interesting Payphone Gives Up Its Secrets

December 11, 2024 by 7 Comments

Reverse engineering a payphone doesn’t sound like a very interesting project, at least in the United States, where payphones were little more than ruggedized versions of residential phones with a coin mechanism attached. Phones in other parts of the world were far more interesting, though, as this look at the mysteries of a payphone from Israel reveals (in Hebrew; English translation here.)

This is a project [Inbar Raz] worked on quite a while ago, but only got around to writing up recently. The payphone in question was sourced from the usual surplus market channels, and appears to have been removed from service by Israeli telecommunications company Bezeq only shortly before he found it. It was in pretty good shape, and was even still locked tight, making some amateur locksmithing the first order of the day. The internals of the phone are surprisingly complex, with a motherboard that looks more like something from a PC. Date codes on the chips and through-hole construction date the device to the early- to mid-1990s.

With physical access gained, [Inbar] turned to the firmware. An Atmel flash chip seemed a good place to look, and indeed he was able to pull code off the chip. That’s where things took a turn thanks to the CPU the code was written for — the CDP1806, a later version of the more popular but still fringe CDP1802. This required [Inbar] to fall down the rabbit hole of writing a new processor definition file for Ghidra so that the firmware could be reverse-engineered. This got him to the point of understanding 1806 assembly well enough that he was able to re-flash the phone to print debugging messages on the built-in 16×2 LCD screen, which allowed him to figure out which routines were being called under various error conditions.

It doesn’t appear that [Inbar] ever completed the reverse engineering project, but as he points out, what does that even mean? He got inside, took a look around, and made the phone do some cool things it couldn’t do before, and in the process made things easier for anyone working with 1806 processors in Ghidra. That’s a pretty complete win in our books.

Using AI To Help With Assembly

November 7, 2024 by 30 Comments

Although generative AI and large language models have been pushed as direct replacements for certain kinds of workers, plenty of businesses actually doing this have found that using this new technology can cause more problems than it solves when it is given free reign over tasks. While this might not be true indefinitely, the real use case for these tools right now is as a kind of assistant to certain kinds of work. For this they can be incredibly powerful as [Ricardo] demonstrates here, using Amazon Q to help with game development on the Commodore 64.

The first step here was to generate code that would show a sprite moving across the screen. The AI first generated code in all caps, as was the style at the time of the C64, but in [Ricardo]’s development environment this caused some major problems, so the code was converted to lowercase. A more impressive conversion was done in the next steps, as the program needed to take advantage of the optimizations found in the Assembly language. With the code converted to 6502 Assembly that can run on the virtual Commodore, [Ricardo] was eventually able to show four sprites moving across the screen after several iterations with the AI, as well as change the style of the sprites to arbitrary designs.

Although the post is a bit over-optimistic on Amazon Q as a tool specifically for developers, it might have some benefits over other generative AIs especially if it’s capable at the chore of programming in Assembly language. We’d love to hear anyone with real-world experience with this and whether it is truly worth the extra cost over something like Copilot or GPT 4. For any of these generative AI models, though, it’s probably worth trying them out while they’re in their early stages. Keep in mind that there’s a lot more than programming that can be done with some of them as well.

Seven New Street Fighter 2 Arcade Rom Hacks

October 23, 2024 by 2 Comments

[Sebastian Mihai] is a prolific programmer and hacker with a particular focus on retrocomputing and period games, and this latest hack, adding new gameplay elements to Capcom’s Street Fighter II – Champion Edition, is another great one. [Sebastian] was careful to resist changing the game physics, as that’s part of what makes this game ‘feel’ the way it does, but added some fun extra elements, such as the ability to catch birds, lob barrels at the other player, and dodge fire.

The title screen was updated for each of the different versions, so there is no doubt about which was being played. This work was based on their previous hacks to Knights of the Round. Since both games shared the same Capcom CPS-1 hardware, the existing 68000 toolchain could be reused, reducing the overhead for this new series of hacks. Continue reading “Seven New Street Fighter 2 Arcade Rom Hacks” →

Quake In 276 KB Of RAM

October 5, 2024 by 20 Comments

Porting the original DOOM to various pieces of esoteric hardware is a rite of passage in some software circles. But in the modern world, we can get better performance than the 386 processor required to run the 1993 shooter for the cost of a dinner at a nice restaurant — with plenty of other embedded systems blowing these original minimum system requirements out of the water.

For a much tougher challenge, a group from Silicon Labs decided to port DOOM‘s successor, Quake, to the Arduino Nano Matter Board platform instead even though this platform has some pretty significant limitations for a game as advanced as Quake.

To begin work on the memory problem, the group began with a port of Quake originally designed for Windows, allowing them to use a modern Windows machine to whittle down the memory usage before moving over to hardware. They do have a flash memory module available as well, but there’s a speed penalty with this type of memory. To improve speed they did what any true gamer would do with their system: overclock the processor. This got them to around 10 frames per second, which is playable, but not particularly enjoyable. The further optimizations to improve the FPS required a much deeper dive which included generating lookup tables instead of relying on computation, optimizing some of the original C programming, coding some functions in assembly, and only refreshing certain sections of the screen when needed.

On a technical level, Quake was a dramatic improvement over DOOM, allowing for things like real-time 3D rendering, polygonal models instead of sprites, and much more intricate level design. As a result, ports of this game tend to rely on much more powerful processors than DOOM ports and this team shows real mastery of their hardware to pull off a build with a system with these limitations. Other Quake ports we’ve seen like this one running on an iPod Classic require a similar level of knowledge of the code and the ability to use assembly language to make optimizations.

Thanks to [Nicola] for the tip!

From High Level Language To Assembly

September 18, 2024 by 24 Comments

If you cut your teeth on Z-80 assembly and have dabbled in other assembly languages, you might not find much mystery in creating programs using the next best thing to machine code. However, if you have only used high level languages, assembly can be somewhat daunting. [Shikaan] has an introductory article aimed to get you started at the “hello world” level of x86-64 assembly language. The second part is already up, too, and covers control structures.

You can argue that you may not need to know assembly language these days, and we’ll admit it’s certainly not as important as it used to be. However, there are unusual cases where you really need either the performance or the small footprint, which is only possible in assembly language. What’s more, it is super useful to be able to read assembly from your high-level tools when something goes wrong.

Of course, one of the problems is that each assembly language is different. For example, knowing that the x86 assembly doesn’t completely transfer to ARM instructions. However, in most cases, the general concepts apply, and it is usually fairly easy to learn your second, third, or fourth instruction set.

We’ve had our own tutorials on this topic. You can also debate if you should learn assembly first or wait, although in this case, the audience is people who waited.

2024 Tiny Games Contest: A Flappy Seagull Game With Sound In Only 500 Bytes

September 12, 2024 by 4 Comments

It was probably a reasonable assumption that the “Tiny” in our recently concluded Tiny Games Contest mostly referred to the physical footprint of the game. And indeed, that’s the way most of the entries broke, which resulted in some pretty amazing efforts. [Anders Nielsen], however, took the challenge another way and managed to stuff a seagull-centric side-scroller into just 500 bytes of code.

That’s not to say that the size of [Anders]’s game is physically huge either. Flappy Larus, as he calls his game, runs on his popular 65uino platform, a 6502 microcontroller in the familiar Arduino Uno form factor. So it’s pretty small to begin with, and doesn’t even need any additional components other than the tiny OLED screen which has become more or less standard for the 65uino at this point. The only real add-on is a piezo speaker module, which when hooked up to the I2C data line happens to make reasonable approximations of a squawking seagull, all without adding a single byte of code. Check out a little game play in the video below.

Flappy Larus may be pretty simplistic, but as we recall, the game it’s based on was similarly minimalist and still managed to get people hooked. The 2024 Tiny Games contest is closed now, but if you’ve got an idea for a tiny game, we’d still love to feature it. Hit the tip line and we’ll take a look! Continue reading “2024 Tiny Games Contest: A Flappy Seagull Game With Sound In Only 500 Bytes” →

A black device with a monochrome LCD sits on a wooden table. It's keyboard extends below the frame. On the screen is the "Level 29" BBS service login.

Internet Appliance To Portable Terminal

August 8, 2024 by 2 Comments

Few processors have found themselves in so many different devices as the venerable Z80. While it isn’t powerful by modern standards, you can still use devices like this Cidco MailStation as a terminal.

The MailStation was originally designed as an email machine for people who weren’t onboard with this whole computer fad, keeping things simple with just an adjustable monchrome LCD, a keyboard, and a few basic applications. [Joshua Stein] developed a terminal application, msTERM, for the MailStation thanks to work previously done on decoding this device and the wealth of documentation for Z80 assembly.

While [Stein] designed his program to access BBSes, we wonder if it might be a good way to do some distraction-free writing. If that wasn’t enough, he also designed the WiFiStation dongle which lets you communicate over a network without all that tedious mucking about with parallel ports.

If you’d like something designed specifically for writing, how about an AlphaSmart? Wanting to build your own Z80-based project? Why not start with an Altoids-sized Z80 SBC, but don’t wait forever since Z80 production finally ended in June.

Continue reading “Internet Appliance To Portable Terminal” →