[Discuss-gnuradio] Problems when using GPSDO

[Wu Ting]

Hi all,

 

I have two questions for using GPSDO. First, I’m now using usrp_source.get_time_now().get_frac_secs() to get a time value like this:

              0.53928493

My question is how accurate is this value. I don’t know much about GPS, so I hope my question is not so stupid: is this value as accurate as PPS?

 

Another question. I’m now using message_sink and msg_queue to receive data from USRP. The sampling rate is 4MHz. I do some calculation for all the data in the msg_queue one by one and write some of them into a file. Now I want to know the accurate time when certain data were produced from USRP. But when I process some data, they already have been produced for a while (they have to spend certain time in msg_queue). I’m also trying to use get_time_now().get_frac_secs() when msg_queue is empty and take this value as the beginning time of the next message. But this method seems to be awkward and not accurate. Is there any idea for this problem?

 

I’m really new to GNURadio, and I have learned a lot from this mail list recently. Thanks.

 

Wu