I've recently been given a RaspberryPi 3 B+ and have made some measurements, the results of which may be of use/interest to fellow users (since info on GPIO pin characteristics seems rather thin on the ground):-
1) With a GPIO pin configured simply as an input via the RPi.GPIO library (pull-up/down state unaltered from its default value) the pin shows slight hysteresis with thresholds at 1.16V and 1.27V, as measured at DC.
2) In the PYTHON interpreter, an intruction to change the state of an output pin in response to a change in state of an input pin takes only about 5 nanoseconds to do its thing.
1) With a GPIO pin configured simply as an input via the RPi.GPIO library (pull-up/down state unaltered from its default value) the pin shows slight hysteresis with thresholds at 1.16V and 1.27V, as measured at DC.
2) In the PYTHON interpreter, an intruction to change the state of an output pin in response to a change in state of an input pin takes only about 5 nanoseconds to do its thing.