Absolute time stamps

Hi all,

I need to get the absolute time from a GPS receiver such as this
:http://www.trimble.com/timing/thunderbolt-e.aspx?dtID=overview into
USRP2 for time stamping the input samples.How can I get RS-232 output
from the trimble receiver into the USRP2?
Can it be done through the DEBUG(a mictor connector) interface of the
FPGA? If yes, do I need to change any firmware? Or is there any other
way?

Can somebody please help me with this?

Mark.