A Modular Logic Analyzer For FPGAs

May 26, 2019 by Lewin Day 4 Comments

When working on a project, it’s incredibly helpful to be able to visualize the various signals in play. This is important when attempting to determine if what is supposed to be happening is actually happening. However, logic analyzers can be expensive, so a group from [Bruce Land]’s ECE5760 class developed their own hardware solution instead.

The primary idea behind the project is modularity. The basic building blocks of the logic analyser are coded in Verilog. They’re designed so that the number of channels and added functions can be mixed and match to suit the given purpose and the capabilities of the target FPGA platform. The team’s logic analyzer is also capable of decoding SPI and I2C in hardware, and has a graphical user interface running on an attached laptop for visualizing signals.

It’s a tidy build, and an excellent project to learn the fundamentals of both FPGA programming and the various communications protocols involved. [Bruce Land]’s classes are a hotbed of FPGA projects, from pokerbots to NES chiptune emulators. Video after the break.

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Teardown: AppLights Personalized Projection

February 27, 2019 by Tom Nardi 22 Comments

Listen, it hurts to hear, but somebody needs to say it. It’s over, OK? You’ve got to admit it and move on. Sure, you could get away with it for a week or two in January, but now it’s just getting weird. No matter how hard you fight it, the facts are the facts: the holidays are over. It’s time to pack up all those lights and decorations before the neighbors really start talking.

But don’t worry, because there’s an upside. Retailers are now gearing up for their next big selling season, which means right now clearance racks the world over are likely to be playing home to holiday lights and decor. That wouldn’t have been very interesting to the average hacker or maker a few years ago, after all, there’s only so much you can do with a string of twinkle lights. But today, holiday decorations are dripping with the sort of high-tech features you’d expect from gadgets that are actively aiming to be obsolete within the next ten months or so.

Case in point, the “AppLights Personalized Projection” which I found sulking around the clearance section of the Home Depot a couple weeks back. This device advertises the ability to project multi-color custom messages and animations on your wall, and is configured over Bluetooth with a companion application on your Android or iOS device. At a minimum we can assume the device must contain a fairly powerful RGB LED, an LCD to shine the light through, and some sort of Bluetooth-compatible microcontroller. For $20 USD, I thought it was worth taking a shot on.

Around this time last year, the regular Hackaday reader may recall I did a teardown for a Christmas laser projector. Inside we found red, green, and blue lasers of considerable power, as well as all the optics and support hardware to get them running. It was a veritable laser playground for $14. Let’s see if the AppLights projector turns out to be a similar electronic cornucopia, and whether or not we’ve got a new Hackaday Holiday tradition on our hands.

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Preserving Floppy Disks Via Logic Analyser

January 8, 2019 by Lewin Day 27 Comments

The floppy disk is a technology that is known only to the youth of today as the inspiration for the Save icon. There’s a lot of retro computing history tied up in these fragile platters, thus preservation is key. But how to go about it? [CHZ-Soft] has found an easy way, using a logic analyzer and a healthy dose of Python.

Floppy drives have particularly low-level interfaces, offering up little more than a few signals to indicate the position of the head on the disk, and pulses to indicate changes in magnetic flux. The data is encoded in the pattern of flux changes. This has important implications as far as preservation goes – it’s best to record the flux changes themselves, and create an image of the exact magnetic state of the disk, and then process that later, rather than trying to decode the disk at the time of reading and backing up just the data itself. This gives the best likelihood of decoding the disk and preserving an accurate image of floppy formats as they existed in the real world. It’s also largely platform agnostic – you can record the flux changes, then figure out the format later.

[CHZ-Soft] takes this approach, explaining how to use a Saleae logic analyser and a serial port to control a floppy drive and read out the flux changes on the disk. It’s all controlled automatically through a Python script, which automates the process and stores the results in the Supercard Pro file format, which is supported by a variety of software. This method takes about 14MB to store the magnetic image of a 720KB disk, and can even reveal a fingerprint of the drive used to write the disk, based on factors such as jitter and timing.

It’s an impressive hack that shows that preservation-grade backups of floppy disks can be achieved without spending big money or using specialist hardware. We’ve seen other projects in this space before, too.

X-Ray Vision For FPGAs: Using Verifla

November 9, 2018 by Al Williams 3 Comments

Last time I talked about how I took the open source Verifla logic analyzer and modified it to have some extra features. As promised, this time I want to show it in action, so you can incorporate it into your own designs. The original code didn’t actually capture your data. Instead, it created a Verilog simulation that would produce identical outputs to your FPGA. If you were trying to do some black box simulation, that probably makes sense. I just wanted to view data, so I created a simple C program that generates a VCD file you can read with common tools like gtkwave. It is all on GitHub along with the original files, even though some of those are not updated to match the new code (notably, the PDF document and the examples).

If you have enough pins, of course, you can use an external logic analyzer. If you have enough free space on the FPGA, you could put something like SUMP or SUMP2 in your design which would be very flexible. However, since these analyzers are made to be configurable from the host computer, they probably have a lot of circuitry that will compete with yours for FPGA space. You configure Verifla at compile time which is not as convenient but lets it have a smaller footprint.

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Logic Analyzers For FPGAs: A Verilog Odyssey

October 12, 2018 by Al Williams 10 Comments

Sometimes you start something simple and then it just leads to a chain reaction of things. I wanted to write a post about doing state machines in Verilog and target the Lattice iCEstick board that we often use for quick FPGA projects. That led to a small problem: how do you show what’s going on inside? In this series of posts, we’ll look at building a logic analyzer into an FPGA to help debug itself, instantiating memory, and — finally — state machines.

Logic analysis is a common tool in FPGA development. If you use Altera, they have Signal Tap available that lets you build a simple logic analyzer into the FPGA that talks back to your PC. Xilinx has ChipScope which is about the same. Sometimes those tools either cost money or are limited in some way in the free versions. I have my sights set on a tool that can be used with the Lattice architecture.

Sure, you can ship data out on I/O pins and then use a regular logic analyzer to pick up the data. But that isn’t very handy. So I thought about writing a generic logic analyzer component. But before I did I decided to check to see if someone else had already done it.

Spoiler alert: they did, but I wanted something a little different so I wound up extending the program significantly. What I wound up with is a reasonably portable Verilog logic analyzer that can produce traces like this one:

Keep in mind, this isn’t a simulation. This is real data pulled off the actual FPGA. Yes, that is gtkwave producing the plots, but the input data is a VCD file generated from samples taken inside the FPGA.

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Quantifying Latency In Cheap RC Transmitters

February 26, 2018 by Tom Nardi 58 Comments

For those just starting out in the world of RC, a low cost transmitter like the Flysky FS-i6S can be very compelling. But is buying a cheap transmitter setting yourself up for failure down the line? The general feel in the RC community has been that cheaper transmitters have higher latency or “lag” on their inputs, which is precisely the kind of thing you want to avoid when flying along at 40+ MPH. As such, the general wisdom has been that your transmitter is one area where you don’t want to cheap out.

Wanting to put that theory to the test, [Marek Baczynski] set out to compare the response time between the Flysky FS-i6S and the more established Taranis X9D. In the video after the break, he uses his Saleae logic analyzer to time how long it takes movement on the transmitter sticks to get interpreted as servo commands at the receiver.

[Marek] connects the logic analyzer directly to the gimbals of both transmitters, allowing him to see user input before any processing is done by the electronics. It’s particularly interesting to see how the smooth analog curves of the gimbals are converted to a “staircase” digital output.

The final results of the latency test end up being fairly surprising. To put it simply: the cheaper Flysky radio not only more accurately interprets the user’s input, but does it considerably faster than the Taranis. [Marek] says he was so surprised by these results that he re-ran the test three times to verify.

But even taking into account the apparently higher fidelity of the cheap radio, he cautions you shouldn’t swap out your gear just yet. Higher end transmitters have a number of other features which make them worth hanging on to, even if the newer generation of radios is slightly faster. The real takeaway from this video is that if you’re just getting into the RC game, these cheaper transmitters aren’t necessarily the kiss of death the community makes them out to be.

Experiments like this and the recent detailed analysis of common hobby motors show just how seriously people take the world of RC. It’s unlikely this single experiment will quell the debate about “cheap” RC transmitters, but perhaps it’s a start.

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Spite, Thrift, And The Virtues Of An Affordable Logic Analyzer

January 3, 2018 by Dan Maloney 44 Comments

[Larry Wall], the father of Perl, lists the three great virtues of all programmers: Laziness, Impatience, and Hubris. After seeing that Saleae jacked up the prices on their popular logic analyzers to ludicrous levels, [CNLohr] added a fourth virtue: Spite. And since his tests with a Cypress FX3 over the last few days may lead to a dirt-cheap DIY logic analyzer, we may soon be able to add another virtue: Thrift.

The story begins a year or two ago when [CNLohr] got a Cypress FX3 development board for $45. The board sat unused for want of a Windows machine, but after seeing our recent article on a minimalist logic analyzer based on an FX2, he started playing with the board to see if it could fan the flames of his Saleae hatred. The FX3 is a neat little chip that has a 100-MHz General Programmable Interface (GPIF) bus that basically lets it act like an easy to use FPGA.

Prepared to spend months on the project, he was surprised to make significant progress on his mission of spiteful thrift within a few days, reading 16 bits off the GPIF at over 200 megabytes per second and dumping it over the USB 3.0 port. [Charles]’ libraries for the FX3 lay the foundation for a lot of cool stuff, from logic analyzers to SDRs and beyond — now someone just has to build them.

The search for a cheap but capable logic analyzer is nothing new, of course. Last year, both [Jenny List] and [Bil Herd] looked at the $22 iCEstick as a potential Saleae beater.

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