Re: [Discuss-gnuradio] Transmission time control from python level

[Josh Blum]

On 07/07/2012 09:30 AM, Nazmul Islam wrote:
> I have three USRP's and I want them to transmit a continuous stream of
> repeated GLFSR source in non-overlapping manner. In other words, each
> transmitter will transmit the source for 1 second and then pause for 5
> seconds. All transmitters will transmit during the 'odd' seconds so that
> there is a 1 second gap between the sources. This process should continue
> for ever.
> 
> Currently, I am controlling the starting and stopping time of the flow
> graphs to achieve my goals. Unfortunately, the code/flowgraph sometimes
> hangs after 15-20 starts. I am using the following code:
> 
> ............
> tb = GLFSR_transmitter()   # The Tx flowgraph : GLFSR source (float) -->
> RRC filter --> USRP Sink
> 
> var = 1
> 
> while var == 1:     # This process should run forever
> 
>      time.sleep(1-time.time() + int(time.time()))
> 
>      condition = ((int(time.time())%6) == 0)       # The transmitter will
> transmit after every 6 seconds
> 
>      if (condition):
> 
>           print time.time()
> 
>           tb.start()
> 
>           sleep(1)      # The transmitter runs for 1 second
> 
>           tb.stop()
> 
>           tb.wait()
> ............................
> 

You really dont want to stop and start the flow graph. TX streams can be
controlled with stream tags. Links to header docs and example here:
http://code.ettus.com/redmine/ettus/projects/uhd/wiki/GNU_Radio_UHD#Using-UHD-with-GNU-Radio

> My USRP's don't seem to like this frequent starting and stopping of flow
> graphs, especially when I am transmitting at 15-20 MS/s rate. I am using
> USRP N210 (SBX daughterboards) and the latest gnuradio images. What other
> things can I do to achieve this timing control? I am looking for options in
> python level since my C++ OOP background is not strong. Josh talked about
> some python based blocks (
> ttps://github.com/guruofquality/gnuradio/tree/python_blocks2<https://github.com/guruofquality/gnuradio/tree/python_blocks2>)
> in (http://old.nabble.com/How-to-implement-a-TDMA-system-td33727749.html).
> They seem to be merged to the master (
> http://gnuradio.org/redmine/projects/gnuradio/repository/revisions/f8581fb475267e1a97eaab962e423559fb4bfce2)
> but I can't find the blocks.
> 

All that stuff + instructions and coding guide can be found here
https://github.com/guruofquality/grextras/wiki

-josh