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[Discuss-gnuradio] how is the FPGA taking effect in USRP???!!!

From: Bill Stevenson
Subject: [Discuss-gnuradio] how is the FPGA taking effect in USRP???!!!
Date: Mon, 17 Mar 2008 20:59:54 -0700 (PDT)

Hello, everyone

I dug up the wfm_rcv_gui.py example file in order to penetrate the principle of GNURadio. But I have 2 questions about it:

1, there is a digital downconverter at the receiver, the function of down converting the signal is performed by the FPGA or the software on PC?

2, if it is done by FPGA, how is the code transmitted to the FPGA? I mean, the code should be written using VHDL or Verilog, but now the code is compiled using Python! How is this transformation done?

Thank u!!!

#!/usr/bin/env python

from gnuradio import gr, eng_notation
from gnuradio import audio
from gnuradio import usrp
from gnuradio import blks
from gnuradio.eng_option import eng_option
from optparse import OptionParser
import sys
import math

from gnuradio.wxgui import stdgui, fftsink
import wx

class wfm_rx_graph (stdgui.gui_flow_graph):
    def __init__(self,frame,panel,vbox,argv):
        stdgui.gui_flow_graph.__init__ (self,frame,panel,vbox,argv)

        IF_freq = parseargs(argv[1:])
        adc_rate = 64e6

        decim = 250
        quad_rate = adc_rate / decim               # 256 kHz
        audio_decimation = 8
        audio_rate = quad_rate / audio_decimation  # 32 kHz
        # usrp is data source
        src = "" (0, decim)
        src.set_rx_freq (0, IF_freq)address@hidden

        guts = blks.wfm_rcv (self, quad_rate, audio_decimation)
        # sound card as final sink
        audio_sink = audio.sink (int (audio_rate))
        # now wire it all together
        self.connect (src, guts)
        self.connect (guts, (audio_sink, 0))

        if 1:
            pre_demod, fft_win1 = \
                       fftsink.make_fft_sink_c (self, panel, "Pre-Demodulation",
                                                512, quad_rate)
            self.connect (src, pre_demod)
            vbox.Add (fft_win1, 1, wx.EXPAND)

        if 1:
            post_deemph, fft_win3 = \
                         fftsink.make_fft_sink_f (self, panel, "With Deemph",
                                                  512, quad_rate, -60, 20)
            self.connect (guts.deemph, post_deemph)
            vbox.Add (fft_win3, 1, wx.EXPAND)

        if 1:
            post_filt, fft_win4 = \
                       fftsink.make_fft_sink_f (self, panel, "Post Filter",
                                                512, audio_rate, -60, 20)
            self.connect (guts.audio_filter, post_filt)
            vbox.Add (fft_win4, 1, wx.EXPAND)

def parseargs (args):
    nargs = len (args)
    if nargs == 1:
        freq1 = float (args[0]) * 1e6
        sys.stderr.write ('usage: wfm_rcv freq1\n')
        sys.exit (1)

    return freq1 - 128e6

if __name__ == '__main__':
    app = stdgui.stdapp (wfm_rx_graph, "WFM RX")
    app.MainLoop ()

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