Count Leading Zeros For Efficient Logarithms

February 7, 2023 by Chris Lott 14 Comments

[Ihsan Kehribar] points out a clever trick you can use to quickly and efficiently compute the logarithm of a 32-bit integer. The technique relies on the CLZ instruction which counts the number of leading zeros in a machine word and is available in many modern processors. Typical algorithms used to compute logarithms are not quick and have a variable execution time depending on the input value. The technique [Ihsan] is using is both fast and has a constant run time.

The above equation summarized the math behind the algorithm. We get the first term easily using the CLZ instruction. Using the remainder and a pre-computed lookup table, it is possible to get the second term to various degrees of accuracy, depending on how big you make the table and whether or not you take the performance hit of interpolation or not — those of a certain age will no likely groan at the memory of doing interpolation by hand from logarithm tables in high school math class. [Ihsan] has posted an MIT-licensed implementation of this technique in his GitHub repository, which includes both the C-language algorithm and Python tools to generate the lookup table and evaluate the errors.

Why would you do this? Our first thought was real-time streaming DSP operations, where you want fast and deterministic calculations, and [Ihsan]’s specifically calls out embedded audio processing as one class of such applications. And he should know, after all, since he developed a MIDI capable polyphonic FM synthesizer on a Cortex M0 that we covered way back in 2015.

All About USB-C: Manufacturer Sins

February 7, 2023 by Arya Voronova 85 Comments

People experience a variety of problems with USB-C. I’ve asked people online about their negative experiences with USB-C, and got a wide variety of responses, both on Twitter and on Mastodon. In addition to that, communities like r/UsbCHardware keep a lore of things that make some people’s experience with USB-C subpar.

In engineering and hacking, there’s unspoken things we used to quietly consider as unviable. Having bidirectional power and high-speed data on a single port with thousands of peripherals, using nothing but a single data pin – if you’ve ever looked at a schematic for a proprietary docking connector attempting such a feat, you know that you’d find horrors beyond comprehension. For instance, MicroUSB’s ID pin quickly grew into a trove of incompatible resistor values for anything beyond “power or be powered”. Laptop makers had to routinely resort to resistor and one-wire schemes to make sure their chargers aren’t overloaded by a laptop assuming more juice than the charger can give, which introduced a ton of failure modes on its own.

When USB-C was being designed, the group looked through chargers, OTG adapters, display outputs, docking stations, docking stations with charging functions, and display outputs, and united them into a specification that can account for basically everything – over a single cable. What could go wrong?

Of course, device manufacturers found a number of ways to take everything that USB-C provides, and wipe the floor with it. Some of the USB-C sins are noticeable trends. Most of them, I’ve found, are manufacturers’ faults, whether by inattention or by malice; things like cable labelling are squarely in the USB-C standard domain, and there’s plenty of random wear and tear failures.

I don’t know if the USB-C standard could’ve been simpler. I can tell for sure that plenty of mistakes are due to device and cable manufacturers not paying attention. Let’s go through the notorious sins of USB-C, and see what we can learn. Continue reading “All About USB-C: Manufacturer Sins” →

MicroPython ESP32 IDE Makes Life Simpler

February 7, 2023 by Al Williams 49 Comments

In theory, using MicroPython on the ESP32 is easy — just flash an image and connect using a serial port. But that leaves a lot of things you still have to do. You need to move files between the two platforms. You’ll want to manage network configurations. You might want better editing and assistance, too. So there are a number of IDEs made to help you and one we recently noticed was MPY-Jama.

The IDE provides source code editing, of course. But it also allows you to do things like pull information about the network using a dashboard or connect to a WiFi network easily. You can even create your own AP with a simple interface.

Although the front part of the README mentions it is for Windows or Mac, if you scroll down you’ll find instructions for installing under Linux. The IDE is extensible using “Jama Funcs” and can handle the flashing operation from inside the IDE.

Of course, there is an IDE from Arduino (but not the Arduino IDE) that handles MicroPython. You can also find a rundown of several similar alternatives online. If you need some inspiration for a MicroPython project, perhaps you’d like to play a game?

OG DOOM Shows Off The Origins Of Multi-Monitor

February 7, 2023 by Jonathan Bennett 13 Comments

We have a thing for DOOM, and we admit it. The source was released, and clever hackers have ported the engine to every system imaginable. It’s a right of passage, when hacking a machine, to run DOOM on it — be it a VoIP phone, or tractor. But the original 1993 release does have a few notable tricks, and there’s something to be said for recreating that experience on period hardware. And that’s what we’re covering today: [Tech Tangents] discovered DOOM’s multi-monitor support, and built a 4-computer cluster to show it off.

There is a catch, of course. DOOM 1.1 has the multi-monitor support, and under-the-hood, it works by running a copy of the game on individual computers, and controlling the drones over the network. As the game’s network code was updated for version 1.2, the multi-monitor feature was axed to make the network code easier to maintain. So, find a 1.1 shareware release, install it on a DOS machine with IPX drivers, and start each iteration with a -net flag. Use -left and -right to set the drones to the appropriate view. And that view is ninety degrees left and right.

Maybe not ideal, but at the time it was one of the first games to have any sort of multi-monitor support at all. Likely inspired by a commercial flight simulator setup. Either way, it’s a neat feature, and kudos to [Tech Tangents] for showing off this obscure feature of a beloved classic!

Continue reading “OG DOOM Shows Off The Origins Of Multi-Monitor” →