Re: [Discuss-gnuradio] Some questions regarding timestamps on packets

[Eric Blossom]

On Tue, Aug 19, 2008 at 02:53:57PM -0700, call5_99 wrote:
> 
> Hello,
>        I am new to GNU radio. So far I have been playing with benchmark_rx
> and benchmark_tx. Now, I am trying to estimate the distance between the
> transmitter and the receiver. For this I need a very accurate timestamp on
> my packets. So my questions are-
> 
> 1) I need the time stamp in the order of nano seconds. Is it possible to get
> such accurate timestamp with GNU radio?

The best we're likely to do with the USRP is 1/64e6 == 15.625ns
This is based on the frequency of the master clock in the FPGA.
The master clock is not locked to any kind of a global reference.

> 2) How do I add timestamp on packet headers? Though I saw many posts on
> packets with timestamp, I didn't find any, which explained how I go about
> adding the timestamp at transmitter end, and retrieve  it at receiving end. 

Folks are working on sorting out the code that handles timestamps right now.

Eric