Re: [Discuss-gnuradio] Triggering USRP at given GPS time from GNU Radio

[Martin]

On 23-02-15 21:33, Piotr Krysik wrote:
> Hi all,
>
> Whenever I want to trigger USRP with at given time with use of a GPSDO
> I'm adding something like this at the end of a constructor of a topblock
> generated by gnuradio-companion:
>
>          if start_time!="":
>              self.start_time_epoch =
> time.mktime(time.strptime(start_time,'%d.%m.%Y %H:%M:%S'))
>
> self.uhd_usrp_source_0.set_start_time(uhd.time_spec_t(self.start_time_epoch))
>
>
> where start_time is a string parameter containing the time at which the
> device should start reception.
>
> The snippet might be useful for others trying to do the same thing.
This is usefull to me indeed. Thanks.
> I want to ask you if there is a way to do better than that and generate
> directly in gnuradio-companion a flowgraph that use GPSDO of USRP to
> trigger it without having to edit anything manually?
I have not found a way yet.
I always edit manually and add a few lines of code, like you seem to do.
(See the end of this mail)

For this application it would be helpfull if you could set the 
start_time from grc.

In general it would be very helpfull if you could add your own python 
code to grc without having to edit it manually after generating.

A "codeblock" in a similar way the import block is implemented would be 
very helpful. Just a block where you can add code. You should probably 
be able to choose where the code is added.

  at the top of the file after all imports
  at the beginning of the constructor of the flowgraph
  at the end of the constructor of the flow_graph
  as a seperate method of the flowgraph
  at the start of main
  at the end of main.

We could make it a feature request.
Or maybe I should just implement it.

Here follows my code snippet to set the start of capturing in the near 
future. This also works if you do not have a GPSDO
You need to set a start_time in the near future which I do like this:

        # In grc add a parameter delay (in seconds) with type float and 
default 0.5
        # at the end of     def __init__ () of the generated flowgrapg 
add the following code:
        #
        self.init_timed_streaming(self.delay)

    def init_timed_streaming(self, delay):
        # You can optionally set the time in the usrp to zero or to 
something else
        # with set_time_now() or if you have a GPSDO with 
set_time_unknown_pps()
        # or set_time_next_pps()
        #self.uhd_usrp_source.set_time_next_pps(uhd.time_spec_t(0))
        #self.uhd_usrp_source.set_time_unknown_pps(uhd.time_spec_t(0))
        #time.sleep(2)

        # Now get the time from the usrp before streaming has started .
        # You can use either uhd_usrp_source or uhd_usrp_sink to get 
the time now.
        tnow = self.uhd_usrp_source.get_time_now()

        # If you have a GPSDO installed tnow is the absolute time
        # locked to the GPS time it received.
        # If you do not have a GPSDO time then this time is just a
        # meaningless number which started somewhere in the past.
        # tnow is of type uhd.time_spec_t

        self.reasonable_delay = delay
        # delay in seconds into the future, this should be at least
        # an order of magnitude larger then the round trip time to USRP

        # capture and transmit will start at t0
        self.t0  = tnow + uhd.time_spec_t(self.reasonable_delay)
        self.t0_secs = self.t0.get_real_secs() # the time in secs (full 
+ fractional) as a floating point number
        print "tnow secs = ", tnow.get_real_secs()
        print "t0_secs = ", self.t0_secs

        #Now you can set the start time of the uhd_usrp_source and/or 
of the uhd_usrp_sink
        # If you set the start_time of both then you can build a system
        # where source and sink start at the exact same moment. This
        # can be usefull in several situations.
        self.uhd_usrp_source.set_start_time (self.t0 )
        self.uhd_usrp_sink.set_start_time (self.t0 )


Best regards,

Martin Dudok van Heel

> Best Regards,
> Piotr Krysik
>
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio