[Discuss-gnuradio] Rx and Tx on same antenna

[Mirko Heukemes]

Hello,

I'm starting to play around with gnuradio and the USRP1. I have the 
RFX400 daughterboard but only one antenna. I used the examples 
usrp_wfm_rcv.py and usrp_nbfm_rcv.py for testing and it worked (I only 
had to change the center frequencies for the use with the FRX400). For 
emitting I used gnuradio-companion and the WBFM transmit block that also 
worked fine. Now, I'm trying to set up a transceiver that uses for both 
the receive and emit path the TX/RX antenna of the RFX400. I made a 
first (simple) flowgraph using different classes for the Rx and Tx paths 
(classes copied from working grc flowgraphs). I used the same parameters 
than for the receiver and emitter alone but I set the transmit parameter 
of the USRP sink to Auto T/R. Now, my plan is to remain in the reception 
mode all the time and to switch to transmission mode only if I want to 
speak. In order to do this, I added this code to my  python script:

if __name__ == '__main__':
   parser = OptionParser(option_class=eng_option, usage="%prog: [options]")
   (options, args) = parser.parse_args()
   tr = usrp_wbfm_receive_nogui()
   tt = usrp_wbfm_emit_rfx400()
   while 1:
       tr.start()
       raw_input('Press Enter to emit: ')
       tr.stop()
       tt.start()
       raw_input('Press Enter to stop emitting ')
       tt.stop()

And both the reception and transmission seem to work in first place. But 
if I press Enter the second time, I get this error message:

RuntimeError: top_block::start: top block already running or wait() not 
called after previous stop()

Assuming that it's impossible to restart a block after stopping it 
without executing the wait() call, I added tr.wait() and tt.wait() after 
the respective stop calls. But then I get another error message:

audio_alsa_sink[plughw:0,0]: snd_pcm_hw_params failed: File descriptor 
in bad state
RuntimeError: check topology failed on audio_alsa_sink(1) using 
ninputs=1, noutputs=0

It seems to be linked to the fact that the alsa driver won't switch back 
to it's receive config after the transmission. Is there a possibility to 
make my script work or am I doing it all the wrong way?

Thanks for your help

Mirko

PS: I've joined the complete code to show the context of my script

#!/usr/bin/env python
##################################################
# Gnuradio Python Flow Graph
# Title: USRP WBFM Receive no gui
# Author: Example
# Description: WBFM Receive with RFX400
# Generated: Thu May 20 11:44:32 2010
##################################################

from gnuradio import audio
from gnuradio import blks2
from gnuradio import gr
from gnuradio.eng_option import eng_option
from grc_gnuradio import usrp as grc_usrp
from optparse import OptionParser

class usrp_wbfm_receive_nogui(gr.top_block):

        def __init__(self):
                gr.top_block.__init__(self, "USRP WBFM Receive no gui")

                ##################################################
                # Blocks
                ##################################################
                self.audio_out = audio.sink(32000, "plughw:0,0", True)
                self.u_source = grc_usrp.simple_source_c(which=0, side="A", 
rx_ant="TX/RX")
                self.u_source.set_decim_rate(200)
                self.u_source.set_frequency(433500000, verbose=True)
                self.u_source.set_gain(20)
                self.wfm_demod = blks2.wfm_rcv(
                        quad_rate=320000,
                        audio_decimation=10,
                )

                ##################################################
                # Connections
                ##################################################
                self.connect((self.u_source, 0), (self.wfm_demod, 0))
                self.connect((self.wfm_demod, 0), (self.audio_out, 0))

class usrp_wbfm_emit_rfx400(gr.top_block):

        def __init__(self):
                gr.top_block.__init__(self, "USRP WBFM transmit")

                ##################################################
                # Blocks
                ##################################################
                self.audio_out = audio.source(32000, "plughw:0,0", True)
                self.multiply = gr.multiply_const_vcc((9000, ))
                self.u_sink = grc_usrp.simple_sink_c(which=0, side="A")
                self.u_sink.set_interp_rate(400)
                self.u_sink.set_frequency(433500000, verbose=True)
                self.u_sink.set_gain(0)
                self.u_sink.set_enable(True)
                self.wbfm_mod = blks2.wfm_tx(
                        audio_rate=32000,
                        quad_rate=320000,
                        tau=50e-6,
                        max_dev=75e3,
                )

                ##################################################
                # Connections
                ##################################################
                self.connect((self.multiply, 0), (self.u_sink, 0))
                self.connect((self.wbfm_mod, 0), (self.multiply, 0))
                self.connect((self.audio_out, 0), (self.wbfm_mod, 0))



if __name__ == '__main__':
        parser = OptionParser(option_class=eng_option, usage="%prog: [options]")
        (options, args) = parser.parse_args()
        tr = usrp_wbfm_receive_nogui()
        tt = usrp_wbfm_emit_rfx400()
        while 1:
                #tr.start()
                #raw_input('Press Enter to emit: ')
                #tr.stop()
                #tr.wait()
                tt.start()
                raw_input('Press Enter to stop emitting ')
                tt.stop()
                tt.wait()
                tr.start()
                raw_input('Press Enter to emit: ')
                tr.stop()
                tr.wait()