[time-nuts] Linux PPS clues?

[Ilia Platone]

Hi all,
I need some clues on the Linux PPS subsystem.
I am trying to take some timestamps of events on a GPIO using an ARM 
SBC, and noticed that the kernel linux can be interfaced to a PPS 
signal, wanted to sync another GPIO to a GPS receiver for time 
reference. I need to know how much precise this system can be. How much 
resolution can I obtain with a cheap receiver (maximum quantization 
frequency)?
Formulas are well accepted.

Thanks,
Ilia.