Hi all, I want to support fpga to add a timestamp when the usrp send and receive data package

Hi all,
I need to measure the time of flight with the accuracy in nanosecond,
now I
found an ic that can measure the time in ns. So now I want to support
to read the timestamp when receive and send a data package with
the fpga firmware. Can someone estimate whether the usrp or usrp2 can
achieve my goal without the performance drop? And is there any usrp fpga
source document available?

Hi all,
I learn from some document that usrp have take a timestamp in nanosecond
with the data package. Can anyone tell me more detail about that? Since
have not receive usrp board I can not do the experiment to confirm it.