Get yourself a Black Magic Probe. It's JTAG/SWD on the device end, USB GDB server on the host end. https://hackaday.com/2016/12/02/black-magic-probe-the-best-

Get yourself a Black Magic Probe. It's JTAG/SWD on the device end, USB GDB server on the host end. https://hackaday.com/2016/12/02/black-magic-probe-the-best-arm-jtag-debugger/ https://hackaday.com/2016/12/02/black-magic-probe-the-best-a... disclaimer: I'm friends with the BMP manufacturer.