#!/usr/bin/env python

#narrow band FM receiver - requires usrp board as input
from gnuradio import gr,audio, eng_notation,usrp, optfir,blks
from gnuradio.eng_option import eng_option
from optparse import OptionParser
from gnuradio.blks import fm_demod_cf

class my_graph(gr.flow_graph):
	def __init__(self,frequency):
		gr.flow_graph.__init__(self)		
		
		#Put flow graph stuff here

		#Create USRP data source
		u = usrp.source_c(decim_rate=250)

		#Tell USRP what daughter board to use and displays name
		#(0,0) means side A, 1st channel - picks daughterboard
		rx_subdev_spec = (0,0)
		u.set_mux(usrp.determine_rx_mux_value(u,rx_subdev_spec))
		subdev = usrp.selected_subdev(u,rx_subdev_spec)
		print "Using daughterboard",subdev.name() 

		#Tune it to supplied frequency
		u.tune(0,subdev,frequency)

		#creates a file to contain the usrp data and connects it
		#to usrp
		usrp_sink = gr.file_sink(gr.sizeof_gr_complex,"usrp.dat")
		self.connect(u,usrp_sink)

		#create the channel filter coefficients
		chan_taps = optfir.low_pass(
			1.0,	#Filter gain
			256e3,	#Sample Rate
			8000,	#one sided modulation BW (edge of passband)
			9000,   #one sided channel BW (edge of stopband)
			0.1,	#Passband ripple
			60)	#Stopband Attenuation

		print "Channel filter taps:", len(chan_taps)

		#creates the channel filter with the coef found above
		#offset adjusted for Sharlene's USRP
		chan = gr.freq_xlating_fir_filter_ccf(
			8,	#Decimation rate
			chan_taps,  #coefficients
			-5000,	#Offset frequency - could be used to shift 
			256e3)  #incoming sample rate

		#creates a file for the output of the channel filter
		chan_sink = gr.file_sink(gr.sizeof_gr_complex,"chan.dat")
		self.connect(chan,chan_sink)

		#connect the usrp output to the channel filter input
		self.connect(u,chan)

		#create the FM demodulator
		demod = fm_demod_cf(self,
			32e3,  #Sample Rate at input
			1,  #Decimation  
			5000,#Deviation
			3000, #edge of audio passband
			4000)  #edge of audio stopband

		#NOte:  a decimation factor of 4 would have been used above
		#to reduce the sample rate to 8Ks/s - but audio board requires
		#at least 44.1Ks/s so 1 was used and resampler below was
		#added

		#add file to collect output of demodulator
		demod_sink = gr.file_sink(gr.sizeof_float,"demod.dat")
		self.connect(demod,demod_sink)

		#connect channel filter to demodulator
		self.connect(chan,demod)


		spkr = audio.sink(48000)

		#insert resampler to increase sample rate of 32K to 48K
		# mult by 3 and divide by 2
		rsamp = blks.rational_resampler_fff(self,3,2)

		#add file to collect output of resampler
		rsamp_sink = gr.file_sink(gr.sizeof_float,"rsamp.dat")
		self.connect(rsamp,rsamp_sink)


		#connect demod to resampler and resampler to speaker
		self.connect(demod,rsamp)
		self.connect(rsamp,spkr)

#The main function
def main():

	parser = OptionParser(option_class=eng_option)
	parser.add_option("-f","--freq",type="eng_float",default=350,
			help="set frequency to FREQ", metavar="FREQ")
	(options,args) = parser.parse_args()
	print "User defined frequency", options.freq		
			
	fg = my_graph(options.freq)
	try:
		fg.run()
	except KeyboardInterrupt:
		pass
main()