#!/usr/bin/env python
#
# python code for gnuradio
#
# generate a binary continuous-phase fsk (cpfsk) signal using pseudo-random data
#
# sample rate, carrier freq, data rate, and freq shift are adjustable

from gnuradio import gr
from gnuradio import audio
import sys
import math

def build_graph ():

# ===== USER DEFINABLE PARAMETERS BETWEEN THESE LINES =====
# assign frequencies (units: Hz)
# frequency shift is distance between the two FSK tones
	sample_rate = 8000
	carrier_freq = 1000
	data_rate = 100
	freq_shift = 50
# ===== USER DEFINABLE PARAMETERS BETWEEN THESE LINES =====

 	m=int(sample_rate/data_rate)
# the following assumes data is +0.5/-0.5
	fm_sens=2*math.pi*(freq_shift)/sample_rate

	fg = gr.flow_graph ()

# generate random data and interpolate to sample rate
# for now we'll just use a short prsg sequence
# (later on integrate the binary lfsr generator)
# optionally, a longer string of 0s and 1s is available
	prsg_string = (1,0,0,0,0,0,1,0,0,0,0,1,1,0,0,0,1,0,1,0,0,1,1,1,1,0,1,0,0,0,1,1,1,0,0,1,0,0,1,0,1,1,0,1,1,1,0,1,1,0,0,1,1,0,1,0,1,0,1,1,1,1,1)
#	prsg_string = (0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)
	rng_src = gr.vector_source_s (prsg_string,1)
	bit = gr.short_to_float ()
	scale = gr.add_const_ff (-0.5)
	interp_taps = (1,)*m
	inter = gr.interp_fir_filter_fff(m,interp_taps)
	fg.connect (rng_src, bit)
	fg.connect (bit, scale)
	fg.connect (scale, inter)

# generate complex-envelope fsk signal
	fm_mod = gr.frequency_modulator_fc (fm_sens)
	fg.connect (inter, fm_mod)

# mix complex-envelope signal up to carrier frequency
	rf_src = gr.sig_source_c (sample_rate, gr.GR_SIN_WAVE, carrier_freq, 0.9, 0)
	mixer = gr.multiply_cc ()
	realpart = gr.complex_to_real ()
	fg.connect (fm_mod, (mixer,0) )
	fg.connect (rf_src, (mixer,1) )
	fg.connect (mixer,realpart)

# output to soundcard
	dst = audio.sink (sample_rate)
	fg.connect (realpart, dst)

	return fg

def main ():
	fg = build_graph()
	fg.start()
	raw_input ('Press Enter to quit')
	fg.stop()

if __name__ == '__main__':
	main ()