Playing The Interview Game

April 12, 2021 by Matthew Carlson 37 Comments

Technical interviews are generally dreaded, just like every other interview. However, technical interviews include many elements that non-technical folks might find mystifying or even pointless, such as whiteboard problem solving, take-home assignments, design sessions, or even just straight brain teasers. [Erik McClure] went a bit off the beaten path and started using the factory builder game Factorio as a technical interview.

Many point to the intent behind the problems and tricky questions inherent in whiteboard coding exercises and assert that the focus is not to complete the problem, but rather to expose how a candidate thinks and problem solves. Factorio is all problem-solving as you work as a team to slowly scale up a humble production line to a massive factory, which makes it a good candidate for assessing these sorts of skills. We doubt that the fine developers who wrote the game ever imagined it being used as an interview.

In all likelihood, you probably won’t have a Factorio interview anytime soon as [Erik] estimated each interview would take between eight and twenty hours. But we love the idea of reimagining the interview from a tedious set of problems to solve to an evolving cooperative game. Of course, you can also read more about getting the experience necessary for a job and what companies are looking for in an interview.

A trailer for Factorio is after the break.

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Code Your Own Twitch Chat Controls For Robots — Or Just About Anything Else!

April 8, 2021 by Lewin Day 4 Comments

Twitch Plays Pokemon burst onto the then nascent livestreaming scene back in 2014, letting Twitch viewers take command of a Game Boy emulator running Pokemon Red via simple chat commands. Since then, the same concept has been applied to everything under the sun. Other video games, installing Linux, and even trading on the New York Stock Exchange have all been gameified through Twitch chat.

*TwitchPlaysPokemon* started a craze in crowdsourced control of video games, robots, and just about everything else.

You, thirsty reader, are wondering how you can get a slice of this delicious action. Fear not, for with a bit of ramshackle code, you can let Twitch chat take over pretty much anything in, on, or around your computer.

It’s Just IRC

The great thing about Twitch chat is that it runs on vanilla IRC (Internet Relay Chat). The protocol has been around forever, and libraries exist to make interfacing easy. Just like the original streamer behind Twitch Plays Pokemon, we’re going to use Python because it’s great for fun little experiments like these. With that said, any language will do fine — just apply the same techniques in the relevant syntax.

SimpleTwitchCommander, as I’ve named it on Github, assumes some familiarity with basic Python programming. The code will allow you to take commands from chat in two ways. Commands from chat can be tabulated, and only the one with the most votes executed, or every single command can be acted on directly. Actually getting this code to control your robot, video game, or pet viper is up to you. What we’re doing here is interfacing with Twitch chat and pulling out commands so you can make it do whatever you like. With that said, for this example, we’ve set up the code to parse commands for a simple wheeled robot. Let’s dive in.

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Python Will Soon Support Switch Statements

April 2, 2021 by Adam Zeloof 113 Comments

Rejoice! Gone are the long chains of if…else statements, because switch statements will soon be here — sort of. What the Python gods are actually giving us are match statements. match statements are awfully similar to switch statements, but have a few really cool and unique features, which I’ll attempt to illustrate below.

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Direct Memory Access: Data Transfer Without Micro-Management

March 31, 2021 by Maya Posch 16 Comments

In the most simple computer system architecture, all control lies with the CPU (Central Processing Unit). This means not only the execution of commands that affect the CPU’s internal register or cache state, but also the transferring of any bytes from memory to to devices, such as storage and interfaces like serial, USB or Ethernet ports. This approach is called ‘Programmed Input/Output’, or PIO, and was used extensively into the early 1990s for for example PATA storage devices, including ATA-1, ATA-2 and CompactFlash.

Obviously, if the CPU has to handle each memory transfer, this begins to impact system performance significantly. For each memory transfer request, the CPU has to interrupt other work it was doing, set up the transfer and execute it, and restore its previous state before it can continue. As storage and external interfaces began to get faster and faster, this became less acceptable. Instead of PIO taking up a few percent of the CPU’s cycles, a big transfer could take up most cycles, making the system grind to a halt until the transfer completed.

DMA (Direct Memory Access) frees the CPU from these menial tasks. With DMA, peripheral devices do not have to ask the CPU to fetch some data for them, but can do it themselves. Unfortunately, this means multiple systems vying for the same memory pool’s content, which can cause problems. So let’s look at how DMA works, with an eye to figuring out how it can work for us.
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Bare-Metal STM32: Please Mind The Interrupt Event

March 26, 2021 by Maya Posch 27 Comments

Interruptions aren’t just a staple of our daily lives. They’re also crucial for making computer systems work as well as they do, as they allow for a system to immediately respond to an event. While on desktop computers these interrupts are less prominent than back when we still had to manually set the IRQ for a new piece of hardware using toggle switches on an ISA card, IRQs along with DMA (direct memory access) transfers are still what makes a system appear zippy to a user if used properly.

On microcontroller systems like the STM32, interrupts are even more important, as this is what allows an MCU to respond in hard real-time to an (external) event. Especially in something like an industrial process or in a modern car, there are many events that simply cannot be processed whenever the processor gets around to polling a register. Beyond this, interrupts along with interrupt handlers provide for a convenient way to respond to both external and internal events.

In this article we will take a look at what it takes to set up interrupt handlers on GPIO inputs, using a practical example involving a rotary incremental encoder.

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Lightweight OS For Any Platform

March 22, 2021 by Bryan Cockfield 35 Comments

Linux has come a long way from its roots, where users had to compile the kernel and all of the other source code from scratch, often without any internet connection at all to help with documentation. It was the wild west of Linux, and while we can all rely on an easy-to-install Ubuntu distribution if we need it, there are still distributions out there that require some discovery of those old roots. Meet SkiffOS, a lightweight Linux distribution which compiles on almost any hardware but also opens up a whole world of opportunity in containerization.

The operating system is intended to be able to compile itself on any Linux-compatible board (with some input) and yet still be lightweight. It can run on Raspberry Pis, Nvidia Jetsons, and x86 machines to name a few, and focuses on hosting containerized applications independent of the hardware it is installed on. One of the goals of this OS is to separate the hardware support from the applications, while being able to support real-time tasks such as applications in robotics. It also makes upgrading the base OS easy without disrupting the programs running in the containers, and of course has all of the other benefits of containerization as well.

It does seem like containerization is the way of the future, and while it has obviously been put to great use in web hosting and other network applications, it’s interesting to see it expand into a real-time arena. Presumably an approach like this would have many other applications as well since it isn’t hardware-specific, and we’re excited to see the future developments as people adopt this type of operating system for their specific needs.

Thanks to [Christian] for the tip!

Getting Started With FreeRTOS And ChibiOS

March 18, 2021 by Maya Posch 15 Comments

If operating systems weren’t so useful, we would not be running them on every single of our desktop systems. In the same vein, embedded operating systems provide similar functionality as these desktop OSes, while targeting a more specialized market. Some of these are adapted versions of desktop OSes (e.g. Yocto Linux), whereas others are built up from the ground up for embedded applications, like VxWorks and QNX. Few of those OSes can run on a microcontroller (MCU), however. When you need to run an OS on something like an 8-bit AVR or 32-bit Cortex-M MCU, you need something smaller.

Something like ChibiOS (‘Chibi’ meaning ‘small’ in Japanese), or FreeRTOS (here no points for originality). Perhaps more accurately, FreeRTOS could be summarized as a multi-threading framework targeting low-powered systems, whereas ChibiOS is more of a full-featured OS, including a hardware abstraction layer (HAL) and other niceties.

In this article we’ll take a more in-depth look at these two OSes, to see what benefits they bring. Continue reading “Getting Started With FreeRTOS And ChibiOS” →