[Commit-gnuradio] r4175 - gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm

[trondeau]

Author: trondeau
Date: 2006-12-20 18:28:48 -0700 (Wed, 20 Dec 2006)
New Revision: 4175

Added:
   
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/benchmark_ofdm_tx.py
   
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/receive_path.py
   
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/transmit_path.py
Log:
moving towards OFDM usage on USRP -- this is currently broken

Added: 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/benchmark_ofdm_tx.py
===================================================================
--- 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/benchmark_ofdm_tx.py
                           (rev 0)
+++ 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/benchmark_ofdm_tx.py
   2006-12-21 01:28:48 UTC (rev 4175)
@@ -0,0 +1,78 @@
+#!/usr/bin/env python
+#
+# Copyright 2005, 2006 Free Software Foundation, Inc.
+# 
+# This file is part of GNU Radio
+# 
+# GNU Radio is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+# 
+# GNU Radio is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with GNU Radio; see the file COPYING.  If not, write to
+# the Free Software Foundation, Inc., 51 Franklin Street,
+# Boston, MA 02110-1301, USA.
+# 
+
+from gnuradio import gr, gru, modulation_utils
+from gnuradio import usrp
+from gnuradio import eng_notation
+from gnuradio.eng_option import eng_option
+from optparse import OptionParser
+
+import random, time, struct, sys, math
+
+# from current dir
+from transmit_path import transmit_path
+
+class my_graph(gr.flow_graph):
+    def __init__(self, callback, occupied_tones, fftsize, symbol_length, rho):
+        gr.flow_graph.__init__(self)
+        self.txpath = transmit_path(self, occupied_tones, fftsize, 
symbol_length)
+
+# /////////////////////////////////////////////////////////////////////////////
+#                                   main
+# /////////////////////////////////////////////////////////////////////////////
+
+def main():
+
+    def send_pkt(payload='', eof=False):
+        return fg.txpath.send_pkt(payload, eof)
+
+    # build the graph
+    fg = my_graph(rx_callback, options)
+
+    r = gr.enable_realtime_scheduling()
+    if r != gr.RT_OK:
+        print "Warning: failed to enable realtime scheduling"
+
+    fg.start()                       # start flow graph
+
+    # generate and send packets
+    nbytes = int(1e6 * options.megabytes)
+    n = 0
+    pktno = 0
+    pkt_size = int(options.size)
+
+    while n < nbytes:
+        send_pkt(struct.pack('!H', pktno) + (pkt_size - 2) * chr(pktno & 0xff))
+        n += pkt_size
+        sys.stderr.write('.')
+        #if options.discontinuous and pktno % 5 == 4:
+        #    time.sleep(1)
+        pktno += 1
+        
+    send_pkt(eof=True)
+    fg.wait()                       # wait for it to finish
+
+if __name__ == '__main__':
+    try:
+        main()
+    except KeyboardInterrupt:
+        pass


Property changes on: 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/benchmark_ofdm_tx.py
___________________________________________________________________
Name: svn:executable
   + *

Added: 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/receive_path.py
===================================================================
--- 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/receive_path.py
                                (rev 0)
+++ 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/receive_path.py
        2006-12-21 01:28:48 UTC (rev 4175)
@@ -0,0 +1,254 @@
+#!/usr/bin/env python
+#
+# Copyright 2005,2006 Free Software Foundation, Inc.
+# 
+# This file is part of GNU Radio
+# 
+# GNU Radio is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+# 
+# GNU Radio is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with GNU Radio; see the file COPYING.  If not, write to
+# the Free Software Foundation, Inc., 51 Franklin Street,
+# Boston, MA 02110-1301, USA.
+# 
+
+from gnuradio import gr, gru, blks
+from gnuradio import usrp
+from gnuradio import eng_notation
+import copy
+import sys
+
+# from current dir
+from pick_bitrate import pick_rx_bitrate
+import ofdm
+
+# /////////////////////////////////////////////////////////////////////////////
+#                              receive path
+# /////////////////////////////////////////////////////////////////////////////
+
+class receive_path(gr.hier_block):
+    def __init__(self, fg, demod_class, rx_callback, options):
+
+        options = copy.copy(options)    # make a copy so we can destructively 
modify
+
+        self._verbose            = options.verbose
+        self._rx_freq            = options.rx_freq         # receiver's center 
frequency
+        self._rx_gain            = options.rx_gain         # receiver's gain
+        self._rx_subdev_spec     = options.rx_subdev_spec  # daughterboard to 
use
+        self._bitrate            = options.bitrate         # desired bit rate
+        self._decim              = options.decim           # Decimating rate 
for the USRP (prelim)
+        self._samples_per_symbol = options.samples_per_symbol  # desired 
samples/symbol
+        self._fft_length         = options.fft_length      # number of bins in 
the FFT
+        self._occupied_tones     = options.occupied_tones  # number of used 
carriers
+        self._cp_length          = options.cp_length       # length of the 
cyclic prefix
+        self._fusb_block_size    = options.fusb_block_size # usb info for USRP
+        self._fusb_nblocks       = options.fusb_nblocks    # usb info for USRP
+
+        self._rx_callback   = rx_callback      # this callback is fired when 
there's a packet available
+
+        if self._rx_freq is None:
+            sys.stderr.write("-f FREQ or --freq FREQ or --rx-freq FREQ must be 
specified\n")
+            raise SystemExit
+
+        # Set up USRP source; also adjusts decim, samples_per_symbol, and 
bitrate
+        self._setup_usrp_source()
+
+        ok = self.set_freq(self._rx_freq)
+        if not ok:
+            print "Failed to set Rx frequency to %s" % 
(eng_notation.num_to_str(self._rx_freq))
+            raise ValueError, eng_notation.num_to_str(self._rx_freq)
+    
+        g = self.subdev.gain_range()
+        if options.show_rx_gain_range:
+            print "Rx Gain Range: minimum = %g, maximum = %g, step size = %g" \
+                  % (g[0], g[1], g[2])
+
+        self.set_gain(options.rx_gain)
+
+        self.set_auto_tr(True)                 # enable Auto Transmit/Receive 
switching
+
+        # copy the final answers back into options for use by demodulator
+        options.samples_per_symbol = self._samples_per_symbol
+        options.bitrate = self._bitrate
+        options.decim = self._decim
+
+        # Design filter to get actual channel we want
+        sw_decim = 1
+        chan_coeffs = gr.firdes.low_pass (1.0,                  # gain
+                                          sw_decim * self._samples_per_symbol, 
# sampling rate
+                                          1.0,                  # midpoint of 
trans. band
+                                          0.1,                  # width of 
trans. band
+                                          gr.firdes.WIN_HANN)   # filter type 
+
+        # Decimating channel filter
+        # complex in and out, float taps
+        self.chan_filt = gr.fft_filter_ccc(sw_decim, chan_coeffs)
+        #self.chan_filt = gr.fir_filter_ccf(sw_decim, chan_coeffs)
+
+        self.ofdm_demod = ofdm.ofdm_demod(fg, occupied_tones, fftsize, 
symbol_length, rho)
+        
+        # receiver
+        self.packet_receiver = \
+            blks.demod_pkts(fg,
+                            self.ofdm_demod,
+                            access_code=None,
+                            callback=self._rx_callback,
+                            threshold=-1)
+
+        # Carrier Sensing Blocks
+        alpha = 0.001
+        thresh = 30   # in dB, will have to adjust
+        self.probe = gr.probe_avg_mag_sqrd_c(thresh,alpha)
+        fg.connect(self.chan_filt, self.probe)
+
+        # Display some information about the setup
+        if self._verbose:
+            self._print_verbage()
+            
+        fg.connect(self.u, self.chan_filt, self.packet_receiver)
+        gr.hier_block.__init__(self, fg, None, None)
+
+    def _setup_usrp_source(self):
+        self.u = usrp.source_c (fusb_block_size=self._fusb_block_size,
+                                fusb_nblocks=self._fusb_nblocks)
+        adc_rate = self.u.adc_rate()
+
+        # derive values of bitrate, samples_per_symbol, and decim from desired 
info
+        (self._bitrate, self._samples_per_symbol, self._decim) = \
+            pick_rx_bitrate(self._bitrate, 
self._demod_class.bits_per_symbol(), \
+                            self._samples_per_symbol, self._decim, adc_rate)
+
+        self.u.set_decim_rate(self._decim)
+
+        # determine the daughterboard subdevice we're using
+        if self._rx_subdev_spec is None:
+            self._rx_subdev_spec = usrp.pick_rx_subdevice(self.u)
+        self.subdev = usrp.selected_subdev(self.u, self._rx_subdev_spec)
+
+        self.u.set_mux(usrp.determine_rx_mux_value(self.u, 
self._rx_subdev_spec))
+
+    def set_freq(self, target_freq):
+        """
+        Set the center frequency we're interested in.
+
+        @param target_freq: frequency in Hz
+        @rypte: bool
+
+        Tuning is a two step process.  First we ask the front-end to
+        tune as close to the desired frequency as it can.  Then we use
+        the result of that operation and our target_frequency to
+        determine the value for the digital up converter.
+        """
+        r = self.u.tune(0, self.subdev, target_freq)
+        if r:
+            return True
+
+        return False
+
+    def set_gain(self, gain):
+        """
+        Sets the analog gain in the USRP
+        """
+        if gain is None:
+            r = self.subdev.gain_range()
+            gain = (r[0] + r[1])/2               # set gain to midpoint
+        self.gain = gain
+        return self.subdev.set_gain(gain)
+
+    def set_auto_tr(self, enable):
+        return self.subdev.set_auto_tr(enable)
+        
+    def bitrate(self):
+        return self._bitrate
+
+    def samples_per_symbol(self):
+        return self._samples_per_symbol
+
+    def decim(self):
+        return self._decim
+
+    def carrier_sensed(self):
+        """
+        Return True if we think carrier is present.
+        """
+        #return self.probe.level() > X
+        return self.probe.unmuted()
+
+    def carrier_threshold(self):
+        """
+        Return current setting in dB.
+        """
+        return self.probe.threshold()
+
+    def set_carrier_threshold(self, threshold_in_db):
+        """
+        Set carrier threshold.
+
+        @param threshold_in_db: set detection threshold
+        @type threshold_in_db:  float (dB)
+        """
+        self.probe.set_threshold(threshold_in_db)
+    
+        
+    def add_options(normal, expert):
+        """
+        Adds receiver-specific options to the Options Parser
+        """
+        add_freq_option(normal)
+        if not normal.has_option("--bitrate"):
+            normal.add_option("-r", "--bitrate", type="eng_float", 
default=None,
+                              help="specify bitrate.  samples-per-symbol and 
interp/decim will be derived.")
+        normal.add_option("-R", "--rx-subdev-spec", type="subdev", 
default=None,
+                          help="select USRP Rx side A or B")
+        normal.add_option("", "--rx-gain", type="eng_float", default=None, 
metavar="GAIN",
+                          help="set receiver gain in dB [default=midpoint].  
See also --show-rx-gain-range")
+        normal.add_option("", "--show-rx-gain-range", action="store_true", 
default=False, 
+                          help="print min and max Rx gain available on 
selected daughterboard")
+        normal.add_option("-v", "--verbose", action="store_true", 
default=False)
+        expert.add_option("-S", "--samples-per-symbol", type="int", 
default=None,
+                          help="set samples/symbol [default=%default]")
+        expert.add_option("", "--rx-freq", type="eng_float", default=None,
+                          help="set Rx frequency to FREQ [default=%default]", 
metavar="FREQ")
+        expert.add_option("-d", "--decim", type="intx", default=None,
+                          help="set fpga decimation rate to DECIM 
[default=%default]")
+        expert.add_option("", "--log", action="store_true", default=False,
+                          help="Log all parts of flow graph to files (CAUTION: 
lots of data)")
+
+    # Make a static method to call before instantiation
+    add_options = staticmethod(add_options)
+
+
+    def _print_verbage(self):
+        """
+        Prints information about the receive path
+        """
+        print "Using RX d'board %s"    % (self.subdev.side_and_name(),)
+        print "Rx gain:         %g"    % (self.gain,)
+        print "modulation:      %s"    % (self._demod_class.__name__)
+        print "bitrate:         %sb/s" % 
(eng_notation.num_to_str(self._bitrate))
+        print "samples/symbol:  %3d"   % (self._samples_per_symbol)
+        print "decim:           %3d"   % (self._decim)
+        print "Rx Frequency:    %s"    % 
(eng_notation.num_to_str(self._rx_freq))
+        # print "Rx Frequency:    %f"    % (self._rx_freq)
+
+def add_freq_option(parser):
+    """
+    Hackery that has the -f / --freq option set both tx_freq and rx_freq
+    """
+    def freq_callback(option, opt_str, value, parser):
+        parser.values.rx_freq = value
+        parser.values.tx_freq = value
+
+    if not parser.has_option('--freq'):
+        parser.add_option('-f', '--freq', type="eng_float",
+                          action="callback", callback=freq_callback,
+                          help="set Tx and/or Rx frequency to FREQ 
[default=%default]",
+                          metavar="FREQ")

Added: 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/transmit_path.py
===================================================================
--- 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/transmit_path.py
                               (rev 0)
+++ 
gnuradio/branches/developers/n4hy/ofdm/gnuradio-examples/python/ofdm/transmit_path.py
       2006-12-21 01:28:48 UTC (rev 4175)
@@ -0,0 +1,243 @@
+#
+# Copyright 2005,2006 Free Software Foundation, Inc.
+# 
+# This file is part of GNU Radio
+# 
+# GNU Radio is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+# 
+# GNU Radio is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with GNU Radio; see the file COPYING.  If not, write to
+# the Free Software Foundation, Inc., 51 Franklin Street,
+# Boston, MA 02110-1301, USA.
+# 
+
+from gnuradio import gr, gru, blks
+from gnuradio import usrp
+from gnuradio import eng_notation
+
+import copy
+import sys
+
+# from current dir
+from pick_bitrate import pick_tx_bitrate
+import ofdm
+
+# /////////////////////////////////////////////////////////////////////////////
+#                              transmit path
+# /////////////////////////////////////////////////////////////////////////////
+
+class transmit_path(gr.hier_block): 
+    def __init__(self, fg, modulator_class, options):
+        '''
+        See below for what options should hold
+        '''
+
+        options = copy.copy(options)    # make a copy so we can destructively 
modify
+
+        self._verbose            = options.verbose
+        self._tx_freq            = options.tx_freq         # tranmitter's 
center frequency
+        self._tx_amplitude       = options.tx_amplitude    # digital amplitude 
sent to USRP
+        self._tx_subdev_spec     = options.tx_subdev_spec  # daughterboard to 
use
+        self._bitrate            = options.bitrate         # desired bit rate
+        self._interp             = options.interp          # interpolating 
rate for the USRP (prelim)
+        self._samples_per_symbol = options.samples_per_symbol  # desired 
samples/baud
+        self._fft_length         = options.fft_length      # number of bins in 
the FFT
+        self._occupied_tones     = options.occupied_tones  # number of used 
carriers
+        self._cp_length          = options.cp_length       # length of the 
cyclic prefix
+        self._fusb_block_size    = options.fusb_block_size # usb info for USRP
+        self._fusb_nblocks       = options.fusb_nblocks    # usb info for USRP
+    
+        if self._tx_freq is None:
+            sys.stderr.write("-f FREQ or --freq FREQ or --tx-freq FREQ must be 
specified\n")
+            raise SystemExit
+
+        if self._fft_length < self.occupied_tones:
+            sys.stderr.write("occupied tones must be less than FFT length\n")
+            raise SystemExit
+        if self._fft_length < self._cp_length:
+            sys.stderr.write("cyclic prefix length  must be less than FFT 
length\n")
+            raise SystemExit
+
+        # Set up USRP sink; also adjusts interp, samples_per_symbol, and 
bitrate
+        self._setup_usrp_sink()
+
+        # copy the final answers back into options for use by modulator
+        options.samples_per_symbol = self._samples_per_symbol
+        options.bitrate = self._bitrate
+        options.interp = self._interp
+
+        # Set center frequency of USRP
+        ok = self.set_freq(self._tx_freq)
+        if not ok:
+            print "Failed to set Tx frequency to %s" % 
(eng_notation.num_to_str(self._tx_freq),)
+            raise ValueError
+
+        # Set the USRP for maximum transmit gain
+        # (Note that on the RFX cards this is a nop.)
+        self.set_gain(self.subdev.gain_range()[0])
+
+        # enable Auto Transmit/Receive switching
+        self.set_auto_tr(True)
+
+
+        symbol_length = self._fft_length + self._cp_length
+        self.ofdm_mod = ofdm.ofdm_mod(fg, self._occupied_tones, 
self.fft_length, symbol_length)
+        # transmitter
+        self.packet_transmitter = \
+            blks.mod_pkts(fg,
+                          self.ofdm_mod,
+                          access_code=None,
+                          msgq_limit=4,
+                          pad_for_usrp=True)
+
+        self.amp = gr.multiply_const_cc(1)
+        self.set_tx_amplitude(self._tx_amplitude)
+
+        # Display some information about the setup
+        if self._verbose:
+            self._print_verbage()
+
+        # Create and setup transmit path flow graph
+        fg.connect(self.packet_transmitter, self.amp, self.u)
+        gr.hier_block.__init__(self, fg, None, None)
+
+    def _setup_usrp_sink(self):
+        """
+        Creates a USRP sink, determines the settings for best bitrate,
+        and attaches to the transmitter's subdevice.
+        """
+        self.u = usrp.sink_c(fusb_block_size=self._fusb_block_size,
+                             fusb_nblocks=self._fusb_nblocks)
+        dac_rate = self.u.dac_rate();
+
+        # derive values of bitrate, samples_per_symbol, and interp from 
desired info
+        (self._bitrate, self._samples_per_symbol, self._interp) = \
+            pick_tx_bitrate(self._bitrate, 
self._modulator_class.bits_per_symbol(),
+                            self._samples_per_symbol, self._interp, dac_rate)
+        
+        self.u.set_interp_rate(self._interp)
+
+        # determine the daughterboard subdevice we're using
+        if self._tx_subdev_spec is None:
+            self._tx_subdev_spec = usrp.pick_tx_subdevice(self.u)
+        self.u.set_mux(usrp.determine_tx_mux_value(self.u, 
self._tx_subdev_spec))
+        self.subdev = usrp.selected_subdev(self.u, self._tx_subdev_spec)
+
+
+    def set_freq(self, target_freq):
+        """
+        Set the center frequency we're interested in.
+
+        @param target_freq: frequency in Hz
+        @rypte: bool
+
+        Tuning is a two step process.  First we ask the front-end to
+        tune as close to the desired frequency as it can.  Then we use
+        the result of that operation and our target_frequency to
+        determine the value for the digital up converter.
+        """
+        r = self.u.tune(self.subdev._which, self.subdev, target_freq)
+        if r:
+            return True
+
+        return False
+        
+    def set_gain(self, gain):
+        """
+        Sets the analog gain in the USRP
+        """
+        self.gain = gain
+        self.subdev.set_gain(gain)
+
+    def set_tx_amplitude(self, ampl):
+        """
+        Sets the transmit amplitude sent to the USRP
+        @param: ampl 0 <= ampl < 32768.  Try 8000
+        """
+        self._tx_amplitude = max(0.0, min(ampl, 32767.0))
+        self.amp.set_k(self._tx_amplitude)
+        
+    def set_auto_tr(self, enable):
+        """
+        Turns on auto transmit/receive of USRP daughterboard (if exits; else 
ignored)
+        """
+        return self.subdev.set_auto_tr(enable)
+        
+    def send_pkt(self, payload='', eof=False):
+        """
+        Calls the transmitter method to send a packet
+        """
+        return self.packet_transmitter.send_pkt(payload, eof)
+        
+    def bitrate(self):
+        return self._bitrate
+
+    def samples_per_symbol(self):
+        return self._samples_per_symbol
+
+    def interp(self):
+        return self._interp
+
+    def add_options(normal, expert):
+        """
+        Adds transmitter-specific options to the Options Parser
+        """
+        add_freq_option(normal)
+        if not normal.has_option('--bitrate'):
+            normal.add_option("-r", "--bitrate", type="eng_float", 
default=None,
+                              help="specify bitrate.  samples-per-symbol and 
interp/decim will be derived.")
+        normal.add_option("-T", "--tx-subdev-spec", type="subdev", 
default=None,
+                          help="select USRP Tx side A or B")
+        normal.add_option("", "--tx-amplitude", type="eng_float", 
default=12000, metavar="AMPL",
+                          help="set transmitter digital amplitude: 0 <= AMPL < 
32768 [default=%default]")
+        normal.add_option("-v", "--verbose", action="store_true", 
default=False)
+
+        expert.add_option("-S", "--samples-per-symbol", type="int", 
default=None,
+                          help="set samples/symbol [default=%default]")
+        expert.add_option("", "--tx-freq", type="eng_float", default=None,
+                          help="set transmit frequency to FREQ 
[default=%default]", metavar="FREQ")
+        expert.add_option("-i", "--interp", type="intx", default=None,
+                          help="set fpga interpolation rate to INTERP 
[default=%default]")
+        expert.add_option("", "--log", action="store_true", default=False,
+                          help="Log all parts of flow graph to file (CAUTION: 
lots of data)")
+
+    # Make a static method to call before instantiation
+    add_options = staticmethod(add_options)
+
+    def _print_verbage(self):
+        """
+        Prints information about the transmit path
+        """
+        print "Using TX d'board %s"    % (self.subdev.side_and_name(),)
+        print "Tx amplitude     %s"    % (self._tx_amplitude)
+        print "modulation:      %s"    % (self._modulator_class.__name__)
+        print "bitrate:         %sb/s" % 
(eng_notation.num_to_str(self._bitrate))
+        print "samples/symbol:  %3d"   % (self._samples_per_symbol)
+        print "interp:          %3d"   % (self._interp)
+        print "FFT length:      %3d"   % (self._fft_length)
+        print "Occupied Tones:  %3d"   % (self._occupied_tones)
+        print "CP length:       %3d"   % (self._cp_length)
+        print "Tx Frequency:    %s"    % 
(eng_notation.num_to_str(self._tx_freq))
+        
+
+def add_freq_option(parser):
+    """
+    Hackery that has the -f / --freq option set both tx_freq and rx_freq
+    """
+    def freq_callback(option, opt_str, value, parser):
+        parser.values.rx_freq = value
+        parser.values.tx_freq = value
+
+    if not parser.has_option('--freq'):
+        parser.add_option('-f', '--freq', type="eng_float",
+                          action="callback", callback=freq_callback,
+                          help="set Tx and/or Rx frequency to FREQ 
[default=%default]",
+                          metavar="FREQ")