Is it possible to build a hardware debugger for debugWIRE for less than 10 €? As it turns out, it is. You just have to make a few compromises and also do a little bit of soldering and gluing.Continue reading
You want to make a single step in your program, but the debugger takes you to some unknown area of the program. This was, in fact, my first experience when I tried out Microchip’s MPLAB X IDE debugger on the innocent blinking sketch. Is this a bug or a feature?Continue reading
There has never been an unexpectedly short debugging period in the history of computers
As mentioned in an earlier blog post this year, hardware debuggers are the premier class of embedded debugging tools. However, until today, there were only very few relatively expensive tools around supporting the debugWIRE interface that is used by the classic ATtinys and a few ATmega MCUs.
The good news is that now you can turn an Arduino Uno, Nano, or Pro Mini into a debugWIRE hardware debugger that communicates with
avr-gdb, the AVR version of the GNU project debugger.
When you develop a tool for a protocol that is undocumented, it is not surprising that you will encounter situations you will not have be anticipated. And this was exactly what I experienced developing the hardware debugger dw-link, which connects debugWIRE MCUs to the GDB debugger. Although a substantial part of the debugWIRE protocol has been reverse engineered, I encountered still plenty of surprising situations: Split personality MCUs, stuck-at-one bits in program counters, secret I/O addresses, half-legal opcodes, and more.Continue reading
The above xkcd comic, which is titled Debugger, alludes to the problem that when you try to apply a particular method to itself, you might not get what you asked for. Turing’s Halting problem is a very famous example for this, i.e., you cannot algorithmically decide whether an algorithm terminates on an input. So, does that problem apply to debuggers as well? In particular, I asked myself whether it makes sense to debug the hardware debugger I am developing with itself.Continue reading
Link-time optimization (LTO) is a very powerful compiler-optimization technique. As I noticed, it does not go very well together with debugging object-oriented programs under GCC, at least for AVR MCUs. I noticed that in the context of debugging an Arduino program and it took me quite a while to figure out that LTO is the culprit.Continue reading
Lubarsky’s Law of Cybernetic Entomology: There’s always one more bug
(Who the hell is Lubarsky?)
A new Arduino library has seen the light of day:
SingleWireSerial. It supports single-wire, half-duplex serial communication. By using the input capture feature of the AVR MCUs, it is extremely accurate and supports bitrates up to 250 kbps robustly. And contrary to its title, one can even use it in a two-wire setting.