Re: [Discuss-gnuradio] Sending Data/Messages to GNU Radio via Python Application

[Paul Boven]

Hi,

On 08/09/2019 21:29, Rajen Goradia wrote:
> I am trying to make use of the ZMQ blocks in GNU Radio to act as a 
> server and have a separate python client application send data/messages 
> to GNU Radio. I was successful in getting data out of GNU Radio and 
> using a separate python application such as using the “ZMQ PUSH Sink” 
> block in GNU Radio and using the zmq library in Python 
> (context.socket(zmq.PULL) function) but I was unable to reverse the 
> procedure. Has anybody successfully tried doing this, either with or 
> without using the zmq library or the ZMQ blocks in GNU Radio? Please let 
> me know and thank you for looking.

Happen to have just done this a few weeks ago, to compensate for doppler 
shift on 21cm (Hydrogen line) observations. What worked for me is listed 
below. This should work with Python 2 and GR 3.7 as well, but I ended up 
using GNU Radio 3.8 because astropy requires python 3. The code sends a 
'freq' message, which you can feed to e.g. the command port of a 
Frequency XLAT FIR filter, see the attached image.

#!/usr/bin/python3
# Note: use Python 2 for older versions of GR
import pmt
import zmq
import time

# Open a ZeroMQ publisher socket on localhost, port 5555
context = zmq.Context()
socket = context.socket(zmq.PUB)
socket.bind("tcp://127.0.0.1:5555")

doppler = 0.1

while(1):
  msg = pmt.cons(pmt.intern("freq"), pmt.from_double(doppler))
  sb = pmt.serialize_str(msg)
  socket.send(sb)
  doppler = doppler + 0.1
  time.sleep(1)

# Code ends here

Regards, Paul Boven.

Flowgraph-ZMQ.png
Description: PNG image