Frequency Sensitivity of GPIO Pins
At 1GHz, any kind of single-ended measurement will be 100% rubbish. Be it digital or analog.



EDIT:

It may not be rubbish, if you had taken care of specific voodoo things.


Termination - high frequency signals need termination resistance to preserve integrity.
Shielding - a 1GHz signal becomes very sensitive to noise. You need to keep it out.
Tons of other things I can't think of right now.


Anyway, these boards are made for signals to 30-50 MHz tops.