That said, sometimes its multi-target support is not as friendly as I would like, and I'm not sure if the AARCH64 support is there yet (I used it on the original RasPi and on Chumbys)
Good news is that its open source and I was able to add SAM4L support when I needed it fairly easily.
 See https://github.com/blacksphere/blackmagic and https://1bitsquared.com/products/black-magic-probe
Of course, if you like the BMP, it is worthwhile to buy the real thing to sponsor 1 Bit Squared and the convenient headers/cables.
Let's try versaloon on a bluepill to replace the JTAG Olimex adaptor....