re bmp the remote protocol is reasonably constrained, it's not actually using any of the gdb protocol
it's not very well specified though, behaviour is currently "what the bmp code does"

i tried to implement it in glasgow but only the "i took openocd bitbang applet and hacked the front off it" version works, i did something wrong implementing the gateware side
https://github.com/Stary2001/glasgow/tree/debug-blackmagic