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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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