> Never EVER do actual work in interrupt routine Never? Sometimes you have to in order to adhere to timing requirements. Say we're talking about a USB device.

> Never EVER do actual work in interrupt routine Never? Sometimes you have to in order to adhere to timing requirements. Say we're talking about a USB device. You'd better respond EP0 control requests without data stage under 50ms; USB spec demands that. Even more so, when there's physical safety involved. You might really want to stop that stepper motor long before main loop notices your marker... Then there are those situations you need to do the processing in IRQ or lose (some) of the data due to system constraints. Just never say never.