Flowgraph Python Code
Dial Tone Flowgraph
The following is a dial-tone example using gnuradio-companion (GRC).
When we click the Generate button, the terminal tells us it produced a .py file, so let's open that to examine its code.
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#
# SPDX-License-Identifier: GPL-3.0
#
# GNU Radio Python Flow Graph
# Title: tutorial_three_1
# GNU Radio version: 3.8.0.0
from distutils.version import StrictVersion
if __name__ == '__main__':
import ctypes
import sys
if sys.platform.startswith('linux'):
try:
x11 = ctypes.cdll.LoadLibrary('libX11.so')
x11.XInitThreads()
except:
print("Warning: failed to XInitThreads()")
from gnuradio import analog
from gnuradio import audio
from gnuradio import gr
from gnuradio.filter import firdes
import sys
import signal
from PyQt5 import Qt
from argparse import ArgumentParser
from gnuradio.eng_arg import eng_float, intx
from gnuradio import eng_notation
from gnuradio import qtgui
class tutorial_three_1(gr.top_block, Qt.QWidget):
def __init__(self):
gr.top_block.__init__(self, "tutorial_three_1")
Qt.QWidget.__init__(self)
self.setWindowTitle("tutorial_three_1")
qtgui.util.check_set_qss()
try:
self.setWindowIcon(Qt.QIcon.fromTheme('gnuradio-grc'))
except:
pass
self.top_scroll_layout = Qt.QVBoxLayout()
self.setLayout(self.top_scroll_layout)
self.top_scroll = Qt.QScrollArea()
self.top_scroll.setFrameStyle(Qt.QFrame.NoFrame)
self.top_scroll_layout.addWidget(self.top_scroll)
self.top_scroll.setWidgetResizable(True)
self.top_widget = Qt.QWidget()
self.top_scroll.setWidget(self.top_widget)
self.top_layout = Qt.QVBoxLayout(self.top_widget)
self.top_grid_layout = Qt.QGridLayout()
self.top_layout.addLayout(self.top_grid_layout)
self.settings = Qt.QSettings("GNU Radio", "tutorial_three_1")
try:
if StrictVersion(Qt.qVersion()) < StrictVersion("5.0.0"):
self.restoreGeometry(self.settings.value("geometry").toByteArray())
else:
self.restoreGeometry(self.settings.value("geometry"))
except:
pass
##################################################
# Variables
##################################################
self.samp_rate = samp_rate = 32000
##################################################
# Blocks
##################################################
self.audio_sink_0 = audio.sink(samp_rate, '', True)
self.analog_sig_source_x_1 = analog.sig_source_f(samp_rate, analog.GR_COS_WAVE, 350, 0.1, 0, 0)
self.analog_sig_source_x_0 = analog.sig_source_f(samp_rate, analog.GR_COS_WAVE, 440, 0.1, 0, 0)
##################################################
# Connections
##################################################
self.connect((self.analog_sig_source_x_0, 0), (self.audio_sink_0, 0))
self.connect((self.analog_sig_source_x_1, 0), (self.audio_sink_0, 1))
def closeEvent(self, event):
self.settings = Qt.QSettings("GNU Radio", "tutorial_three_1")
self.settings.setValue("geometry", self.saveGeometry())
event.accept()
def get_samp_rate(self):
return self.samp_rate
def set_samp_rate(self, samp_rate):
self.samp_rate = samp_rate
self.analog_sig_source_x_0.set_sampling_freq(self.samp_rate)
self.analog_sig_source_x_1.set_sampling_freq(self.samp_rate)
def main(top_block_cls=tutorial_three_1, options=None):
if StrictVersion("4.5.0") <= StrictVersion(Qt.qVersion()) < StrictVersion("5.0.0"):
style = gr.prefs().get_string('qtgui', 'style', 'raster')
Qt.QApplication.setGraphicsSystem(style)
qapp = Qt.QApplication(sys.argv)
tb = top_block_cls()
tb.start()
tb.show()
def sig_handler(sig=None, frame=None):
Qt.QApplication.quit()
signal.signal(signal.SIGINT, sig_handler)
signal.signal(signal.SIGTERM, sig_handler)
timer = Qt.QTimer()
timer.start(500)
timer.timeout.connect(lambda: None)
def quitting():
tb.stop()
tb.wait()
qapp.aboutToQuit.connect(quitting)
qapp.exec_()
if __name__ == '__main__':
main()
Once GRC has created a Python file, the user is free to modify it in any desired manner, such as changing parameters, sample rate, and even connections among the blocks.
Warning: After the Python file is modified, running GRC again with that flowgraph will wipe out your changes!
Dial Tone Python code Dissected
While examining the code, we need to get familiar with documentation. GNU Radio uses Doxygen (the software) for the GNU Radio Manual. The easiest way to go through the documentation is to go through the functions that we use so let us simplify our code by only including the bare bones needed to run the dial-tone example.
#!/usr/bin/env Python3
from gnuradio import gr
from gnuradio import audio
from gnuradio import analog
class my_top_block(gr.top_block):
def __init__(self):
gr.top_block.__init__(self)
sample_rate = 32000
ampl = 0.1
src0 = analog.sig_source_f(sample_rate, analog.GR_SIN_WAVE, 350, ampl)
src1 = analog.sig_source_f(sample_rate, analog.GR_SIN_WAVE, 440, ampl)
dst = audio.sink(sample_rate, "")
self.connect(src0, (dst, 0))
self.connect(src1, (dst, 1))
if __name__ == '__main__':
try:
my_top_block().run()
except [[KeyboardInterrupt]]:
pass
Let us examine this line by line:
#!/usr/bin/env python3
Tells the shell that this file is a Python file and to use the Python interpreter to run this file. Should always be included at the top to run from the terminal.
from gnuradio import gr
from gnuradio import audio
from gnuradio import analog
Tells Python the modules to include. We must always have gr to run GNU Radio applications. The audio sink is included in the audio module and the signal_source_f is included in the analog module which is why we include them. PEP8 tells us we should import every module on its own line.
class my_top_block(gr.top_block):
Define a class called "my_top_block" which is derived from another class, gr.top_block. This class is basically a container for the flow graph. By deriving from gr.top_block, we get all the hooks and functions we need to add blocks and interconnect them.
def __init__(self):
Only one member function is defined for this class: the function "init()", which is the constructor of this class.
gr.top_block.__init__(self)
The parent constructor is called (in Python, this needs to be done explicitly. Most things in Python need to be done explicitly; in fact, this is one main Python principle).
sample_rate = 32000
ampl = 0.1
Variable declarations for sampling rate and amplitude that we will later use.
Connecting the Blocks
self.connect(src0, (dst, 0))
self.connect(src1, (dst, 1))
The general syntax for connecting blocks is self.connect(block1, block2, block3, ...) which would connect the output of block1 with the input of block2, the output of block2 with the input of block3 and so on. We can connect as many blocks as we wish with one connect() call. However this only work when there is a one-to-one correspondence. If we go back to our initial flowgraph, there are 2 inputs to the Audio Sink block. The way to connect them is by using the syntax above. The first line connects the only output of src0 (350 Hz waveform) to the first input of dst (Audio Sink). The second line connects the only output of src1 (440 Hz waveform) to the second input of dst (Audio Sink). The code so far is equivalent to the flowgraph we have created in the beginning; the rest of the lines simply start the flowgraph and provide a keyboard interrupt.
if __name__ == '__main__':
try:
my_top_block().run()
except KeyboardInterrupt:
pass
Luckily we are past the early years of GNU Radio when there was no GRC to make the Python files for us. Nowadays we can simply click things together in GRC instead of having to write code in Python to build flowgraphs. Still, a good understanding of what is going on every time we run GRC is good to know as it gives us more control of what we want the program to do.