With this configuration:
[env:disco_l475vg_iot01a]
platform = ststm32
board = disco_l475vg_iot01a
framework = mbed
debug_tool = stlink
And the mbed blinky example.
Despite the breakpoint, the debugger never stops on lines 11 (and 9) when there is myled = 0;
but why ?
see here