We don’t always JTAG, but when we do, we use a Black Magic Probe. It’s a completely open ARM-chip debugging powerhouse. If you program the small ARM chips and you don’t have a BMP, you need a BMP. Right now, one of the main producers of these little gems is running a Kickstarter where you can get your hands on a nicely made one and/or a 1Bitsy STM32F415-based development board.
Why is the BMP so great? First off, it’s got a JTAG and a UART serial port in one device. You can flash the target, run your code, use the serial port for
printf debugging like you know you want to, and then fall back on full-fledged JTAG-plus-GDB when you need to, all in one dongle. It’s just very convenient.
But the BMP’s killer feature is that it runs a GDB server on the probe. It opens up a virtual serial port that you can connect to directly through GDB on your host computer. No need to hassle around with OpenOCD configurations, or to open up a second window to run [texane]’s marvelous st-util. Just run GDB,
target extended-remote /dev/ttyACM0 and you’re debugging. As the links above demonstrate, there are many hardware/software pairs that’ll get you up and debugging. But by combining the debug server with the JTAG hardware, the BMP is by far the slickest.
Full disclosure: we use a BMP that we built ourselves, which is to say that we compiled and flashed the firmware into a $4 STLink clone programmer that we had on hand. Breaking the required signals out required a bit of ugly, fiddly soldering, but we enjoy that sort of thing. If you don’t, the early-bird Kickstarter (with cables) looks like a good deal to us.