Diagram of the LTC protocol, showing the difference between 1 bits and 0 bits - both transmitted using one up and one down pulse, but with '1' bit pulses being half as short.

Animate Arcane Protocols With Interrupt-Backed Bitbanging

June 19, 2022 by Arya Voronova 10 Comments

We often take our “SoftwareSerial” libraries for granted, and don’t investigate what goes on under the hood — until they fail us, at least. Would you like to learn how to harness the power of interrupt-driven bitbanging? [Jim Mack] teaches us how to make our protocol implementations fly using the LTC protocol as a springboard.

LTC (Linear/[Longitudinal] TimeCode) is a widely-used and beautifully-crafted protocol that tends to fly under our radar, and is one that hackers could learn plenty from. It’s used for synchronization of audio/video devices during media production and playback. LTC’s signal is almost digital but not quite: it doesn’t need a clock, and it has no polarity. Additionally, it mimics an audio signal really well, you can decode it at any playback speed, and many other benefits and quirks that [Jim] outlines. You do need to maintain the timings, though, and [Jim]’s article shows us how to keep them right while not inconveniencing your primary tasks.

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Linux Fu: Up Your GDB Game!

June 14, 2022 by Al Williams 19 Comments

If you want to buy a car, there are plenty of choices. If you want to buy a jetliner, there are fewer choices. If you want to use the Large Hadron Collider, you have a choice of exactly one. The harder something is to create, the less likely there is to be many of them. If you are looking for a Linux debugger, there are only a few choices, but gdb is certainly the one you will find most often. There is lldb and a handful of non-open commercial offerings, but for the most part you will use gdb to debug software on Linux.

Of course, not everyone’s a fan of gdb’s text-based interface, so there’s no shortage of front ends available for it. In fact, gdb has two potentially built-in interfaces although depending on how you install gdb, you might not have both of them. Of course, if you use an IDE, it very likely is a front end for gdb among other things. But at the core is gdb and — usually — there is a window somewhere that you can stuff gdb commands into. Even emacs — which might be considered the original IDE — can run gdb and gives you a sort-of GUI experience.

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Yes We Have Random Bananas

June 12, 2022 by Al Williams 36 Comments

If you ask a normal person to pick a random number, they’ll usually just blurt out a number. But if you ask a math-savvy person for a random number, you’ll probably get a lecture about how hard it is to pick a truly random number. But if you ask [Valerio Nappi], you might just get a banana.

His post, which is in two parts, details how what computers generate are actually pseudo-random numbers. You can easily make sure that every number has the same probability of selection as any other number. The problem is that you have to start with something — usually called a seed. For the purposes of playing games, for example, you can grab some source of entropy like how many microseconds since a hardware timer last rolled over, the number of input pulses you’ve received from a mouse lately, or how long you had to wait for the enter key to depress after asking the user to press it. But if you know that seed and the algorithm you can perfectly predict what number the computer will generate next so it isn’t truly random.

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Screenshot of the EFI shell, showing doom.wad and doom.efi in 'ls' command output, and then doom.efi being loaded

DOOM? In Your BIOS? More Likely Than You Think!

June 12, 2022 by Arya Voronova 25 Comments

We’ve seen hackers run DOOM on a variety of appliances, from desk phones to pregnancy tests. Now, the final frontier has been conquered – we got DOOM to run on an x86 machine. Of course, making sure we utilize your PC hardware to its fullest, we have to forego an OS. Here are two ways you can run the classic shooter without the burden of gigabytes of bloated code in the background.

[nic3-14159] implemented this first version as a payload for coreboot, which is an open-source BIOS/UEFI replacement for x86 machines. Some might say it’s imperfect — it has no sound support, only works with PS/2 keyboards, and exiting the game makes your computer freeze. However, it’s playable, and it fits into your BIOS flash chip.

But what if your computer hasn’t yet been blessed with a free BIOS replacement? You might like this UEFI module DOOM port instead, originally made by [Warfish] and then built upon by [Cacodemon345]. To play this, you only need to compile the binary and an UEFI shell, then use the “Load EFI Shell” option in your UEFI menu – something that’s widely encountered nowadays. This version also lacks sound, but is a bit more fully featured due to all the facilities that UEFI provides for its payloads.

Of course there’s far more efficient ways to slay demons on your computer, but even if they aren’t necessarily practical from a gaming standpoint, these two projects serve as decent examples of Coreboot and UEFI payloads. BIOS replacements like coreboot take up so little space, we’ve even seen Windows 3.1 fit alongside coreboot in the BIOS chip. Wondering what UEFI is, even? Here’s a primer for you. And, if you don’t mind the exceptional bloat of a stripped-down Linux install, here’s a Linux image built from the ground up to run DOOM specifically.

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Homebrew An OS From Scratch? Snowdrop Shows How It’s Done

June 11, 2022 by Donald Papp 21 Comments

Ever wondered what it would take to roll your own OS? [Sebastian]’s Snowdrop OS might just provide you with some insight into that process, and maybe even some inspiration.

[Sebastian] created Snowdrop completely from scratch, using only x86 assembly language. It’s more than just bare-bones, and boasts a number of useful utilities and programs including a BASIC interpreter and linker (for creating standalone BASIC executables.) That’s not even touching on the useful essentials, like multitasking and a GUI framework. There are even a number of resources specifically for making game development easier. Because as [Sebastian] puts it, what’s a operating system without games?

Interested in giving Snowdrop a try, or peek at the source code? The binaries and sources section has all you need, and the other headings at the top of the page will send you to the various related goodies. If you have a few minutes, we recommend you watch a walkthrough of the various elements and features of Snowdrop in this video tour (embedded after the page break.)

Snowdrop is an ambitious project, but we’re not surprised that [Sebastian] has made it work; we’ve seen his low-level software skills before, with his fantastic efforts around the classic stand-up arcade game, Knights of the Round.

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PyScript: Python In The Web Browser

June 8, 2022 by Al Williams 25 Comments

A chainsaw can make short work of clearing out the back forty. It can also make a good horror movie. So while some people will say we don’t need another tool to allow more malicious scripting in the browser, we also know that, like any tool, you can use it or abuse it. That tool? PyScript, which is, of course, Python in the browser.

The tool is in the early experimental phase, so the project doesn’t suggest using it in a production environment yet. However, if it works well, the promise is not just that you can write browser-based applications in Python — you’ll have a handy way to reuse existing Python code and even be able to run the same code on the browser that currently runs on the server. This has a lot of implications for improved client/server applications, or cases where you want to be able to run against a local backend when disconnected and a remote backend when you do have a connection. Of course, you can interoperate with JavaScript, too.

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Quantum Computing: The First Taste Is Free

June 5, 2022 by Al Williams 3 Comments

There are a few ways to access real quantum computers — often for free — over the Internet. However, most of these are previous-generation machines that have limited capabilities. Great for learning, perhaps, but not something you could do anything practical with. Xanadu, however, has announced what they claim to be a computer capable of reaching quantum advantage that is free for anyone to use, within limits. Borealis — the computer in question — uses photonic states and has the capability of working with over 216 squeezed-state qubits.

The company is selling time on the computer, but the free tier includes 5 million free shots on Borealis and 10 million shots on an earlier series of quantum computers. You can also buy pay-as-you go service for about $100 per million shots on Borealis.

While a few million shots may sound like a lot, we noticed that the quickstart demo consumes 10,000 shots and that’s presumably something simple. That’s still about 500 runs of that on Borealis — not bad for free on a state-of-the-art quantum computer. You will be wanting to debug with a simulator, though.

We presume the developers are Beatles fans given that you use software called Penny Lane and Strawberry Fields to access the machines. Your job is controlled by Python and there is a cloud simulator to save your shots.

We won’t pretend to understand all there is about squeezed light qubits and the Borealis architecture. But you can get some general practice in our series on quantum computing. Or there are a few lectures around including one that aims at different levels of experience.

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