NIST Helps You With Cryptography

May 25, 2017 by Elliot Williams 33 Comments

Getting cryptography right isn’t easy, and it’s a lot worse on constrained devices like microcontrollers. RAM is usually the bottleneck — you will smash your stack computing a SHA-2 hash on an AVR — but other resources like computing power and flash code storage space are also at a premium. Trimming down a standard algorithm to work within these constraints opens up the Pandora’s box of implementation-specific flaws.

NIST stepped up to the plate, starting a lightweight cryptography project in 2013 which has now come out with a first report, and here it is as a PDF. The project is ongoing, so don’t expect a how-to guide. Indeed, most of the report is a description of the problems with crypto on small devices. Given the state of IoT security, just defining the problem is a huge contribution.

Still, there are some concrete recommendations. Here are some spoilers. For encryption, they recommend a trimmed-down version of AES-128, which is a well-tested block cipher on the big machines. For message authentication, they’re happy with Galois/Counter Mode and AES-128.

I was most interested in hashing, and came away disappointed; the conclusion is that the SHA-2 and SHA-3 families simply require too much state (and RAM) and they make no recommendation, leaving you to pick among less-known functions: check out PHOTON or SPONGENT, and they’re still being actively researched.

If you think small-device security is easy, read through the 22-question checklist that starts on page twelve. And if you’re looking for a good starting point to read up on the state of the art, the bibliography is extensive.

Your tax dollars at work. Thanks, NIST!

And thanks [acs] for the tip!

Balancing Robot Needs Innovative Controller And Motor

May 18, 2017 by Bryan Cockfield 20 Comments

A self-balancing robot is a great way to get introduced to control theory and robotics in general. The ability for a robot to sense its position and its current set of circumstances and then to make a proportional response to accomplish its goal is key to all robotics. While hobby robots might use cheap servos or brushed motors, for any more advanced balancing robot you might want to reach for a brushless DC motor and a new fully open-source controller.

The main problem with brushless DC motors is that they don’t perform very well at low velocities. To combat this downside, there are a large number of specialized controllers on the market that can help mitigate their behavior. Until now, all of these controllers have been locked down and proprietary. SmoothControl is looking to create a fully open source design for these motors, and they look like they have a pretty good start. The controller is designed to run on the ubiquitous ATmega32U4 with an open source 3-phase driver board. They are currently using these boards with two specific motors but plan to also support more motors as the project grows.

We’ve seen projects before that detail why brushless motors are difficult to deal with, so an open source driver for brushless DC motors that does the work for us seems appealing. There are lots of applications for brushless DC motors outside of robots where a controller like this could be useful as well, such as driving an airplane’s propeller.

Microcontroller Load Meter Tells You How Hard It’s Currently Working

May 13, 2017 by Lewin Day 19 Comments

Writing code for embedded applications can be difficult. There are all sorts of problems you can run into – race conditions, conflicting peripherals, unexpected program flow – any of these can cause havoc with your project. One thing that can really mess things up is if your microcontroller is getting stuck on a routine – without the right debugging hardware and software, this can be a tricky one to spot. [Terry] developed a microcontroller load meter just for this purpose.

It’s a simple setup – a routine named loadmeter-task on the microcontroller sends a train of pulses to a mechanical ammeter. The ammeter is then adjusted with a trimpot to read “0” when the chip is unloaded. As other tasks steal CPU time, there’s less time for loadmeter-task to send its pulses, so the meter falls to the left.

Overall it’s a quick and easy bit of code you could add to any project with a spare GPIO pin, that might help you debug. Plus it’s cool to know how hard your project is pushing the silicon.

If you’d like to know more about what your chip is doing, check out this post about the usefulness of in-circuit debugging, or read about Bil Herd’s experiments with ICE and OBD-II.

Using Modern C++ Techniques With Arduino

May 5, 2017 by Rich Hawkes 99 Comments

C++ has been quickly modernizing itself over the last few years. Starting with the introduction of C++11, the language has made a huge step forward and things have changed under the hood. To the average Arduino user, some of this is irrelevant, maybe most of it, but the language still gives us some nice features that we can take advantage of as we program our microcontrollers.

Modern C++ allows us to write cleaner, more concise code, and make the code we write more reusable. The following are some techniques using new features of C++ that don’t add memory overhead, reduce speed, or increase size because they’re all handled by the compiler. Using these features of the language you no longer have to worry about specifying a 16-bit variable, calling the wrong function with NULL, or peppering your constructors with initializations. The old ways are still available and you can still use them, but at the very least, after reading this you’ll be more aware of the newer features as we start to see them roll out in Arduino code.
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FPGA Emulates NES Cart; Prototype So Cyberpunk

April 13, 2017 by Bryan Cockfield 25 Comments

By now, most of us have had some experience getting ROMs from classic video games to run on new hardware. Whether that’s just on a personal computer with the keyboard as a controller, or if it’s a more refined RetrioPie in a custom-built cabinet, it has become relatively mainstream. What isn’t mainstream, however, is building custom hardware that can run classic video games on the original console (translated). The finished project looks amazing, but the prototype blows us away with it’s beauty and complexity.

[phanick]’s project is a cartridge that is able to run games on the Polish Famicon clone called the Pegasus. The games are stored on an SD card but rather than run in an emulator, an FPGA loads the ROMs and presents the data through the normal edge-connector in the cartridge slot of the console. The game is played from the retro hardware itself. It takes a few seconds to load in each ROM, but after that the Pegasus can’t tell any difference between this and an original cartridge.

The original prototype shown here was built back in 2012. Since then it’s been through a few iterations that have reduced the size. PCBs were designed and built in-house, and the latest revision also includes a 3D-printed case that is closer to the size of the original Famicon cartridges.

Even if you don’t have an interest in classic video games or emulation, the video below is worth checking out. (Be sure to turn on the subtitles if you don’t speak Polish.) [phanick] has put in a huge amount of time getting all of the details exactly right, and the level of polish shows in the final product. In fact, we’ve featured him before for building his own Famicom clone.

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Boost Converter Functionality At Rock-Bottom Prices

March 27, 2017 by Bryan Cockfield 16 Comments

Linear voltage regulators are pretty easy to throw into a project if something in it needs a specific voltage that’s lower than the supply. If it needs a higher voltage, it’s almost just as easy to grab a boost converter of some sort to satisfy the power requirements. But if you’re on a mission to save some money for a large production run, or you just like the challenge of building something as simply as possible, there are ways of getting voltages greater than the supply voltage without using anything as non-minimalistic as a boost converter. [Josh] shows us exactly how this can be done using a circuit known as a charge pump to drive a blue LED.

One of the cool things about AVR microcontrollers is that they can run easily on a coin cell battery and source enough current to drive LEDs directly from the output pins. Obviously enough, if the LED voltage is greater than the voltage of the power supply, this won’t work. That is, unless you have a spare diode and capacitor around to build a charge pump.

The negative charge pump works by charging up a capacitor that is connected to an AVR pin, with the other side between the LED and a garden-variety diode to ground. That results in a roughly (VCC – 0.7) volt difference across the capacitor’s plates. When the AVR pin goes low, the other side of the capacitor goes negative by this same amount, and this makes the voltage across the LED high enough to light up. Not only is this simpler than a boost converter, but it doesn’t need any bulky inductors to work properly.

Will this work for any load? Am I going to start any fires by overdriving the LED? Luckily, [josh] answers all of these questions and more on the project page, and goes into some detail on the circuit theory as well. Granted, the charge pump doesn’t have the fine control over the power supply that you can get out of a buck or boost converter (or any switch-mode power supply). But it does have good bang-for-the-buck.

Flashing An ARM With No Soldering

March 20, 2017 by Elliot Williams 7 Comments

[Sami Pietikäinen] was working on an embedded Linux device based on an Atmel SAMA5D3x ARM-A5 processor. Normally, embedded Linux boxes will boot up off of flash memory or an SD card. But if you’re messing around, or just want to sidestep normal operation for any reason, you could conceivably want to bypass the normal boot procedure. Digging around in the chip’s datasheet, there’s a way to enter boot mode by soldering a wire to pull the BMS pin. As [Sami] demonstrates, there’s also a software way in, and it makes use of mmap, a ridiculously powerful Linux function that you should know about.

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