Some resources...

JTAG

tutos/posts

Tjtag-arduino Use the arduino as a JTAG adaptor with Tjtag
Arduiggler Arduino based JTAG cable with UrJTAG
JTAGduino The JTAGduino project has the goal of using Arduino as a JTAG interface
FUJI Free USB JTAG interface
JTAGenum (Arduino-based) scans pins for basic JTAG functionality and can be used to enumerate the IR for undocumented opcodes
JTAGulator open source hardware tool that assists in identifying OCD connections from test points, vias, or component pads on a target device
jtag-finder mirror
Black Magic Probe in-application debugging tool using a JTAG or Serial Wire Debugging (SWD) port. Targets ARM Cortex-M and Cortex-A based microcontrollers.
- HydraBus JTAG/SWD native debugger supported officially in blackmagic github