Wbirk: Yep, agree with all you comments. I rather hoped that using standard raspian/python i might avoid loosing steps by monitoring stepper drive pulses with a input interrupt routine which was connected to the drive pulse pin and i assumed the OS would schedule efficiently. It did work ok to a point, but i was surprised at how low my max slew worked out to be!

I amrelatively new to python, (and indeed a very rusty old coder), so managing Cores is a bit beyond me at the moment - Im at the stage of knowing what i don't know!