Easy Portable Serial Ports

Modern operating systems insulate us — as programmers, especially — from so much work. Depending on how far back you go, programmers had to manage their own fonts, their own allocation space on mass storage, or even their own memory allotments. Every year, though, it seems like things get easier and easier. So why is it so annoying to open a simple serial port? It isn’t hard, of course, but on every operating system it seems to be painful — probably in an attempt to be flexible. And it is even worse if you want portability. I needed to write some C code that read data from an FPGA’s embedded logic analyzer, and I was annoyed at having to write yet more serial port code. I have my own shim library, but it isn’t well tested and isn’t all that flexible — it does what I need, but I wanted something better. What I wound up with the serial library from Sigrok. You know Sigrok? The logic analyzer software.

 You might counter that the serial port is old hat, so no one wants to support it with modern systems. While the physical serial port might be on life support, there’s no shortage of equipment that connects via USB that appears to be a serial port. So while I was talking to an FTDI chip on an FPGA board, you could just as well be talking to an Arduino or a USB voltmeter or anything.

I guess the Sigrok developers had the same problem I did and they took the time to write a nice API and port it to major platforms. Although Sigrok uses it, they maintain it as a separate project and it was just what I needed. Sort of. I say sort of because the version installed with Ubuntu was old and I needed some features on the newest release, but — as usual — the Internet came to the rescue. A quick Git command, and four lines of build instructions and we were ready to go.

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What’s Inside A Neonode Laser Sensor?

Every once in a while, you get your hands on a cool piece of hardware, and of course, it’s your first instinct to open it up and see how it works, right? Maybe see if it can be coaxed into doing just a little bit more than it says on the box? And so it was last Wednesday, when I was at the Embedded World trade fair, and stumbled on a cool touch display floating apparently in mid-air.

The display itself was a sort of focused Pepper’s Ghost illusion, reflected off of an expensive mirror made by Aska3D. I don’t know much more — I didn’t get to bring home one of the fancy glass plates — but it looked pretty good. But this display was interactive: you could touch the floating 2D projection as if it were actually there, and the software would respond. What was doing the touch response in mid-air? I’m a sucker for sensors, so I started asking questions and left with a small box of prototype Neonode zForce AIR sensor sticks to take apart.

The zForce sensors are essentially an array of IR lasers and photodiodes with some lenses that limit their field of view. The IR light hits your finger and bounces back to the photodiodes on the bar. Because the photodiodes have a limited angle over which they respond, they can be used to triangulate the distance of the finger above the display. Scanning quickly among the IR lasers and noting which photodiodes receive a reflection can locate a few fingertips in a 2D space, which explained the interactive part of the floating display. With one of these sensors, you can add a 2D touch surface to anything. It’s like an invisible laser harp that can also sense distance.

The intended purpose is fingertip detection, and that’s what the firmware is good at, but it must also be the case that it could detect the shape of arbitrary (concave) objects within its range, and that was going to be my hack. I got 90% of the way there in one night, thanks to affordable tools and free software that every hardware hacker should have in their toolbox. So read on for the unfortunate destruction of nice hardware, a tour through some useful command-line hardware-hacking tools, and gratuitous creation of animations from sniffed SPI-like data pulled off of some test points.

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Logic Analyzer Pushes the Limits of Miniaturization

Careful not to sneeze while using this diminutive logic analyzer — you could send it flying across the bench.

Undertaken more for the challenge than as a practical bench tool, [Uwe Hermann]’s tiny logic analyzer is an object lesson on getting a usable circuit as small as possible. Sure, some sacrifices had to be made; it’s only an eight-channel instrument without any kind of input protection at all, and lacks niceties like an EEPROM. But that allows it to fit on a mere 11 x 11-mm fleck of PCB. That’s a pretty impressive feat of miniaturization, given that the Cypress microcontroller running the show is in QFN package that takes up 64-mm² all by itself. A micro-USB connector takes up much of the back side of the board and allows the analyzer to talk to sigrok, an open-source signal analysis suite.

Everything about the project is totally open, including the PCB files, so you can build your own if you feel up to the challenge. We’d strongly suggest you check out this primer on logic analyzers first, though, especially since it focuses on the capabilities of the sigrok suite.

Analyzing The 6502 With Python And Cheap Dev Boards

The Before Times were full of fancy logic analyzers. Connect the leads on these analyzers to a system, find that super special ROM cartridge, and you could look at the bus of a computer system in real time. We’ve come a long way since then. Now we have fast, cheap bits of hardware that can look at multiple inputs simultaneously, and there are Open Source solutions for displaying and interpreting the ones and zeros on a data bus. [hoglet] has built a very clever 6502 protocol decoder using Sigrok and a cheap 16-channel logic analyzer.

This protocol decoder is capable of looking at the ones and zeros on the data bus of a 6502-based computer. Right now, [hoglet] able to stream two million 6502 cycles directly to memory, so he’s able to capture the entire startup sequence of a BBC Micro. The hardware for this build was at first an Open Bench Logic Sniffer on a Papilio One FPGA board. This hardware was changed to an impressively inexpensive Cypress FX2 development board that was reconfigured to a 16 channel logic analyzer.

The software stack is where this really shines, and here [hoglet] documented most of the build over on the stardot forums. The basic capture is done with Sigrok, the Open Source signal analysis toolchain. This project goes a bit further than simply logging ones and zeros to a file. [hoglet] designed an entire 6502 protocol decoder with Python. Here’s something fantastic: this was [hoglet]’s first major Python project.

To capture the ones and zeros coming out of a 6502, the only connections are the eight pins on the data bus, RnW, Sync, Rdy, and Phy2. That’s only twelve pins, and no connections to the address bus, but the protocol decoder quickly starts to predict what the current program counter should be. This is a really fantastic piece of work, enabling an entire stack trace on any 6502 computer for less than $20 in parts.

Everything You Need To Know About Logic Probes

We just spent the last hour watching a video, embedded below, that is the most comprehensive treasure trove of information regarding a subject that we should all know more about — sniffing logic signals. Sure, it’s a long video, but [Joel] of [OpenTechLab] leaves no stone unturned.

At the center of the video is the open-source sigrok logic capture and analyzer. It’s great because it supports a wide variety of dirt cheap hardware platforms, including the Salae logic and its clones. Logic is where it shines, but it’ll even log data from certain scopes, multimeters, power supplies, and more. Not only can sigrok decode raw voltages into bits, but it can interpret the bits as well using protocol decoder plugins written in Python. What this all means is that someday, it will decode everything. For free.

[Joel] knows a thing or two about sigrok because he started the incredibly slick PulseView GUI project for it, but that doesn’t stop him from walking you through the command-line interface, which is really useful for automated data capture and analysis, if that’s your sort of thing. Both are worth knowing.

But it’s actually the hardware details where this video shines. He breaks down all of the logic probes on his bench, points out their design pros and cons, and uses that basis to explain just what kind of performance you can expect for $20 or so. You’ll walk away with an in-depth understanding of the whole toolchain, from grabber probes to GUIs.
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Review: DSLogic Logic Analyzer

Logic analyzers historically have been the heavy artillery in an engineer’s arsenal. For many of us, the name invokes mental images of large HP and Tektronix iron with real CRT screens. Logic connections were made through pods, with hundreds of leads weaving their way back to the test equipment. The logic analyzer came out when all else failed, when even a four channel scope wasn’t enough to figure out your problems. Setting them up was a pain – if you were lucky, the analyzer had a PC keyboard interface. If not, you were stuck typing your signal names into the front panel keyboard. Once setup though, logic analyzers were great at finding bugs. You can see things you’d never see with another tool – like a data bus slowly settling out after the read or write strobe.

There have been a number of USB based logic analyzers introduced in recent years, but they didn’t really catch on until Saleae released their “Logic” line of devices. Low cost, high-speed, and easy to use – these devices were perfect. They also inspired an army of clone devices based upon the same Cypress Semiconductor parts. DSLogic designed by DreamSource Labs, can be thought of as an open source evolution of the original Saleae device.

DSLogic appeared in 2013 as a Kickstarter campaign for an open source logic analyzer with an optional oscilloscope extension. I think it’s safe to say that they did well, raising $111,497 USD, more than 10 times their initial goal of $10,000 USD. These days both the DSLogic and the oscilloscope extension are available at The Hackaday Store. In this review we’re focusing on the logic analyzer portion of the tool. 

Click past the break for the full story!

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Turn your BeagleBoneBlack in to a 14-channel, 100Msps Logic Analyzer

The BeagleBoneBlack is a SoC of choice for many hackers – and quite rightly so – given its powerful features. [abhishek] is majoring in E&E from IIT-Kharagpur, India and in 2014 applied for a project at beagleboard.org via the Google Summer of Code project (GSoC). His project, BeagleLogic aims to realize a logic analyzer using the Programmable Real-Time units on board the AM335X SoC family that powers the BeagleBone and the BeagleBone Black.

The project helps create bindings of the PRU with sigrok, and also provides a web-based front-end so that the logic analyzer can be accessed in much the same way as one would use the Cloud9 IDE on the BeagleBone/BeagleBone Black to create a new application with BoneScript.

Besides it’s obvious use as a debugging tool, the logic analyzer can also be a learning tool that can be used to understand digital signals. BeagleLogic turns the BeagleBone Black into a 14-channel, 100Msps Logic Analyzer. Once loaded, it presents itself as a character device node /dev/beaglelogic. In stand-alone mode, it can do binary captures without any special client software. And when used in conjunction with the sigrok library, BeagleLogic supports software triggers and decoding for over 30 different digital protocols.

The analyzer can sample signals from 10Hz upto 100MHz, in 8 or 16 bits and up to a maximum of 14 channels. Sample depth depends on free RAM, and upto 320MB can be reserved for BeagleLogic. There’s also a web interface, which, once installed on the BeagleBone, can be accessed from port 4000 and can be used for low-volume captures (up to 3K samples).

[abhishek] recently added the BeagleLogic Cape which can be used to debug logic circuits up to 5V safely. Source files for BeagleLogic as well as the Cape are available via his github repos. [abhishek] blogged about his project on his website where there’s a lot more information and links to be found. Catch a video of BeagleLogic after the break.

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