Hello Weizhan Song,
The 0.5XF refers to the change rate and it can be up to 0.5 of the clock rate of the module (F), which would be the scenario of changing the value of the IO every clock cycle.
Depending on the module you are using the clock for the module may differ so take that into account and look at what PLLs and divisors are feeding the clock for the module that’s using the GPIO.
I hope this helps!
Regards,
