Hi Francois,
I think you answered your question yourself:
There are ways to query the GPS module; however, these are queries
and do not behave like sample streams or messages. Therefore,
integration with the GRC does not really make much sense.
The GPSDO is just a device that is connected by serial line (and the
clock and pps cables) to your USRP; it does not add any tags. Tags are
a GNU Radio concept that neither the USRP nor UHD know about; your
time, tune and rate tags are attached by the usrp_source GNU Radio
block.
However, if you look into what the GPSDO does (e.g. synchronize your
USRP's clock rate and internal real time clock to GPS),
you will find that reading the rx_time stream tags yield exactly the
information that you could get if there was a pps tag attached to a
sample every second by just counting the samples that you processed
(which GNU Radio does for you), converting the number to an absolute
time (which time_spec_t::from_ticks does for you), and subtracting you
first samples' time.
So, basically, there's an easy way to add your own "every second
there's a tag"-block. But since that seems to be application-specific,
you're bound to write it yourself, which raises the question why you
would do something like that when you can infer the time of each
sample by just looking at its number.
So: Happy hacking,
Marcus
On 09/02/2013 03:10 AM, Francois Quitin wrote:
Hi all,
I'd like to know if it's possible to read the GPSDO data (more specifically the
GPS time) with GNURadio-companion. I understand there are simple commands to
read this data in C++ or python, and I'd like to know if it's possible in GRC.
I'm familiar with programming GRC blocks and working with time-tags. Does the
GPSDO attach some tag on a sample when sending it's pps signal that I could
retrieve in GRC?
Thanks,
Francois
--
Francois Quitin, Ph.D.
Research Fellow
School of Electrical & Electronic Engineering
Nanyang Technological University
Singapore
Phone: +65-8502-3690
Email: address@hidden
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