Cannot step into crt0.s

roland,

Which option are you referring to as greyed out?

With both the ISS and real hardware you can't step until the initial startup code has run and the program has stopped (at alt_main or main usually).

Why do you need to step through crt0.s?

ps. If you are having problems stepping through assembler code without debug information then try doing it in dissasembly mode (the upside down pile of bricks)