[Discuss-gnuradio] Transmission time control from python level

[Nazmul Islam]

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()
............................

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) 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. 

Any suggestion will be appreciated.

Thanks,

Nazmul



-- 
Muhammad Nazmul Islam

Graduate Student
Electrical & Computer Engineering
Wireless Information & Networking Laboratory
Rutgers, USA.