Over the last year or so we’ve noticed a definite uptick in the number of folks using OpenOCD on the Raspberry Pi. It’s a cheap and convenient solution for poking around with various microcontrollers and embedded devices, but not always the most elegant. Looking to improve on the situation somewhat, [Matthew Mets] has been working on a purpose-built JTAG Hat to clean things up a bit.
Onboard level shifters allow you connect to JTAG and SWD interfaces from 1.8 to 5 V, and if you power the target device from the Pi itself, there’s even support for measuring the voltage and current. To connect up to your target, the open hardware board features a “legacy” pin header perfect for jumper wires, as well as a dedicated 10-pin Cortex Debug Connector. Whether you spin up your own or buy one assembled, it certainly looks like a tool worth having around if you often find yourself working with the appropriate chips.
In addition to the design files for the hardware, [Matthew] has also provided some nice documentation on how to get the software side of things up and running. Starting with a blank SD card, it walks you through the initial setup of the Raspberry Pi all the way through the installation and configuration of a patched version of OpenOCD designed to support the JTAG Hat.
Until a few years ago, developing for FPGAs required the use of proprietary locked-down tools, but in the last few years, the closed-source dam has burst, and open-source FPGA tools such as Yosys, SimbiFlow, and Icestorm have come flooding out. Setting up a build environment for these exciting new tools can still be quite a challenge, but [Carlos Eduardo] has decided to make setting up an open-source toolchain for Xilinx FPGAs a breeze with Docker.
His image only has three prerequisites: Docker, Python 3, and OpenOCD (which is used to load your FPGA with your bespoke bitfile). After the Docker image has been built and all of the tools installed, [Carlos] guides you through using Python, FuseSoc, and SymbiFlow to build your first open-source Xilinx FPGA project.
In addition to making setup a whole lot easier, utilizing containers allows the same development environment to be built on Linux, Mac, and Windows (using WSL), which will make life a lot easier for teams working across different OSs. [Carlos’s] Dockerfile is unique because it supports the popular Artix-7 series of FPGAs — for the Lattice FPGAs that have been supported for a lot longer, there are existing Docker files already up on DockerHub. It’s easier than installing the vendor’s toolchain!
As a debugger, GDB is a veritable Swiss Army knife. And just like exploring all of the non-obvious uses of a those knives, your initial response to the scope of GDB’s feature set is likely to be one of bewilderment, subsequent confusion, and occasional laughter. This is an understandable reaction in the case of the Swiss Army knife as one is unlikely to be in the midst of an army campaign or trapped in the wilderness. Similarly, it takes a tricky debugging session to really learn to appreciate GDB’s feature set.
If you have already used GDB to debug some code, it was likely wrapped in the comfort blanket of an IDE. This is of course one way to use GDB, but limits the available features to what the IDE exposes. Fortunately, the command line interface (CLI) of GDB has no such limitations. Learning the CLI GDB commands also has the advantage that one can perform that critical remote debug session even in the field via an SSH session over the 9600 baud satellite modem inside your Swiss Army knife, Cyber Edition.
Have I carried this analogy too far? Probably. But learning the full potential of GDB is well worth your time so today, let’s dive in to sharpen our digital toolsets.
If you’re reading Hackaday, you’ve almost certainly heard of JTAG. There’s an excellent chance you’ve even used it once or twice to reflash an unruly piece of hardware. But how well do you actually know JTAG? More specifically, do you know how useful it can be when reverse engineering hardware?
Whether you’re a JTAG veteran or a novice, this phenomenal guide written by [wrongbaud] is sure to teach you a thing or two. Starting with a low-level explanation of how the interface actually works, the guide takes you though discovering JTAG ports on unknown targets, the current state-of-the-art in open source tools to interact with the device, and finally shows a real-world example of pulling and analyzing a gadget’s firmware.
There’s no way to do his write-up justice with a breakdown or a summary, so we won’t even try. Just get comfortable, maybe grab a drink, and dive in. It’s certainly not a short read, but there isn’t a wasted word on the page. Every piece of the puzzle, from how to figure out an unlabeled pinout to determining the instruction length, is explained in exactly the amount of detail you’re looking for. This is a guide for hackers written by a hacker, and it shows.
It’s amazing to see how much technology is packed into even the “simple” devices that we take for granted in modern life. Case in point, the third party Xbox controller that [wrongbaud] recently decided to tear into. Not knowing what to expect when he cracked open its crimson red case, inside he found an ARM Cortex microcontroller and a perfect excuse to play around with Serial Wire Debug (SWD).
Though even figuring out that much took a bit of work. As is depressingly common, all the interesting components on the controller’s PCB were locked away behind a black epoxy blob. He had no idea what chip was powering the controller, much less that debugging protocols it might support. But after poking around the board with his multimeter, he eventually found a few test points sitting at 3.3 V which he thought was likely some kind of a programming header. After observing that pulling the line labelled “RES” low reset the controller, he was fairly sure he’d stumbled upon a functional JTAG or SWD connection.
As [wrongbaud] explains in his detailed blog post, SWD is something of a JTAG successor that’s commonly used by ARM hardware. Using just two wires (data and clock), SWD provides hardware debugging capabilities on pin constrained platforms. It allows you to step through instructions, read and write to memory, even dump the firmware and flash something new.
For the rest of the post, [wrongbaud] walks the reader through working with an SWD target. From compiling the latest version of OpenOCD and wiring an FTDI adapter to the port, all the way to navigating through the firmware and unlocking the chip so you can upload your own code.
To prove he’s completely conquered the microcontroller, he ends the post by modifying the USB descriptor strings in the firmware to change what it says when the controller is plugged into the computer. From here, it won’t take much more to get some controller macros like rapid fire implemented; a topic we imagine he’ll be covering in the future.
Assembly lines for electronics products are complicated beasts, often composed of many custom tools and fixtures. Typically a microcontroller must be programmed with firmware, and the circuit board tested before assembly into the enclosure, followed by functional testing afterwards before putting it in a box. These test platforms can be very expensive, easily into the tens of thousands of dollars. Instead, this project uses a set of 12 Raspberry Pi Zero Ws in parallel to program, test, and configure up to 12 units at once before moving on to the next stage in assembly.
When a processor has a fault it can leave what looks to be precious little in the way of cause and effect. Debug-by-print-statement works surprisingly well in simple cases, but where in a desktop environment you would drop into a debugger to solve trickier problems this can be an onerous task on an embedded system. [Ross Schlaikjer]’s excellent blog post walks through setting up one of our favorite Open Hardware debug probes and shows us that with the right tooling in place, unexpected faults aren’t quite so impenetrable. Continue reading “Debug Superpowers Bring An STM32 Back From The Dead”→