> (gdb) target extended-remote localhost:3333 Remote debugging using > localhost:3333 0x0001ad90 in ?? ()
That address (0x0001ad90) seems to be in the flash region of the micro:bit memory map: https://github.com/lancaster-university/microbit-targets/blob/3667b701a083c6a8b73385b533179b286abc7848/bbc-microbit-classic-gcc-nosd/ld/NRF51822.ld#L5 So, perhaps when you got this, something was executing from flash when gdb connected and put the target into debug halt? The "??" simply means that the debugger couldn't find symbolic debug information for the address in question so couldn't display a function name. None of this necessarily indicates any problem or erroneous behaviour on the part of OpenOCD/gdb debugging.
