The Orbtrace debugger hardware connected to a development board t hrough a 20-pin ribbon cable. The development board has a green LED shining.

ORBTrace Effort: Open Tool For Professional Debugging

There are some fairly powerful debugging facilities available on today’s microcontrollers — if your code crashes mysteriously, chances are, there’s a debugging interface that could let you track down the exact crash circumstances in no time. Sadly, debugging tools for these powerful interfaces tend to be prohibitively expensive and highly proprietary, thus, not friendly for hobbyists. Now, there’s a community-driven high-capability debugging platform called ORBTrace, brought to us by [mubes] and [zyp].

With parallel trace, you get a constant stream of consciousness, every exact instruction executed by your CPU. [mubes] and [zyp] set out to tap into the power of parallel trace debugging for Cortex-M processors. and the ORBTrace project was born. Relying on the Orbuculum project’s software capabilities, this FPGA-based debugger platform can do parallel trace and the more popular high-speed SWO trace – and way more. ORBTrace has the potential to grow into a powerful debug helper tool, with enough capabilities for anyone to benefit. And of course, it’s fully open-source.

The ORBTrace board, with a FPGA in the center of it, a USB-C connector on the left, and two IDC debug connectors on the right (one ten-pin and one twenty-pin)The ORBTrace platform has plenty of untapped potential. There’s the battle-tested JTAG and SWD that you can already use with all the open tools you could expect. However, there’s also plenty of available resources on the FPGA, including even a currently unutilized RISC-V softcore. If you wanted to add support for any other family of devices to this debugger, sky’s the limit! And, of course, there’s cool software to go with it – for example, orbmortem, which keeps a ring buffer of instructions in memory and shows you the last code executed before your CPU stops, or orbstat, a tool for profiling your embedded code.

If you’re looking to purchase effortless feature parity with Segger or Lauterbach devices, the ORBTrace doesn’t promise that. Instead, it’s an open debugging toolkit project, with hardware available for purchase, and software just waiting for you take control of it. This project’s community hangs out in the 1BitSquared discord’s #orbuculum channel, and gateware’s advancing at a rapid pace – welcoming you to join in on the fun.

ORBTrace is a powerful tool for when your goals become large and your problems become complex. And, being a community-driven experimental effort, we’ll undoubtedly see great things come out of it – like the Mooltipass project, originally developed by Hackaday community members, and still going strong.

SWO: An ARM Printf By Any Other Name

I’ll confess. Although printf-style debugging has a bad rep, I find myself turning to it on occasion. Sure, printf is expensive and brings in a lot of code, but if you have the space and time to use it while debugging you can always remove it before you are finished. However, what if you don’t have an output device or you are using it for something else? If you are using most modern ARM chips, you have another option — a dedicated output channel that is used for several things, including debugging output. I decided I wanted to try that on the Blackpill running mbed, and found out it isn’t as easy as you might think. But it is possible, and when you are done reading, you’ll be able to do it, too.

I’m writing this using the STM32-specific ST-LINK hardware. If you use other JTAG devices like the BlackMagic probe, you probably already have this set up for you.

What You Get

I’ll start backward with the end result, then talk about the software, so you’ll be good and motivated by the time you get to the hardware requirements. Spoiler alert: your existing hardware might need a quick hack to make it work, although you can buy something off the shelf if you prefer.

Here is a very simple test program:

SWO_Channel debugport;  // requires #include "SWO.h"
int main() 
  unsigned count=0;
  debugport.printf("\r\nHello World from SWO\r\n");
  debugport.printf("CPU SystemCoreClock is %d Hz\r\n", SystemCoreClock);

  while (1) 
    led = !led; // flip LED if output is true
    ThisThread::sleep_for(rate); // sleepy time
    if (count % 10) debugport.putc('*'); else debugport.printf("%d\r\n",count); 

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