API for interrupts / callbacks

[raveslave]

have you thought about ways to implement something to allow 2-way async communication? i.e. setting up a callback for a hardware interrupt generated from a "board gpio"/button could also be useful scenarios when you read a sensor that emits its value when its ADC conversion is done, so instead of having a poll loop on the host, it would be nice if a value or fifo can be dispatched on the next (upstream) usb packet transfer => event to belay