Finally an inexpensive and easy to use JTAG solution (hardware+software). Intended for backyard hardware enthusiasts, also known as OpenWRT/LEDE router hackers :-)
Pick yourself a $2 ST-Link dongle (available in many chinese shops), and you will be ready to hack in minutes!
JTAG in a box is distributed as an AppImage. It should run pretty much everywhere and be self-sufficient (on major Linux distributions such as Ubuntu, Fedora or Arch).