1pps input USRP

Hi All,

I want to feed USRP with 1 pps input from io pins. I found from an old
mail that it is already possible.

“You can connect the 1PPS to the digital io pins on the basic or lf
daughtercards. From there you can use the read_io() method in python
to read the value on the pins. Just make sure that your 1PPS is
between about 1.5 and 3.3V; under 1.5V it may not be detected, over
3.3V you could fry a pin.”

Could someone explain a little bit in detail how to do this?
Thank you in advance