/*! \page page_uhd UHD Interface

\section Introduction
This is the GNU Radio UHD package. It is the interface to the UHD
library to connect to and send and receive data between the Ettus
Research, LLC product line. To use the UHD blocks, the Python
namespaces is in gnuradio.uhd, which would be normally imported
as:

\code
    from gnuradio import uhd
\endcode

The relevant blocks are listed in the \ref uhd_blk group.

A quick listing of the details can be found in Python after importing
by using:

\code
    help(uhd)
\endcode


\section External Documentation

Ettus Research keeps the comprehensive documentation to the underlying UHD driver, which can be found:

    http://files.ettus.com/uhd_docs/manual/html/

The UHD Doxygen page is located:

    http://files.ettus.com/uhd_docs/doxygen/html/index.html


\section Typical Setup

A typical option parser setup for a UHD device looks like

\code
    parser = OptionParser(option_class=eng_option)
    parser.add_option("-a", "--args", type="string", default="",
                      help="UHD device address args , [default=%default]")
    parser.add_option("", "--spec", type="string", default=None,
                      help="Subdevice of UHD device where appropriate")
    parser.add_option("-A", "--antenna", type="string", default=None,
                      help="select Rx Antenna where appropriate")
    parser.add_option("-s", "--samp-rate", type="eng_float", default=1e6,
                      help="set sample rate (bandwidth) [default=%default]")
    parser.add_option("-f", "--freq", type="eng_float", default=None,
                      help="set frequency to FREQ", metavar="FREQ")
    parser.add_option("-g", "--gain", type="eng_float", default=None,
                      help="set gain in dB (default is midpoint)")
\endcode

To use these options to create a UHD source object:

\code
    self.u = uhd.usrp_source(device_addr=options.args,
                             io_type=uhd.io_type.COMPLEX_FLOAT32,
                             num_channels=1)

    self.u.set_samp_rate(options.samp_rate)

    # if no gain was specified, use the mid-point in dB
    if options.gain is None:
        g = self.u.get_gain_range()
        options.gain = float(g.start()+g.stop())/2
    self.u.set_gain(options.gain, 0)

    # Set the center frequency
    self.u.set_center_freq(options.freq, 0)

    # Set the subdevice spec
    if(options.spec):
        self.u.set_subdev_spec(options.spec, 0)

     # Set the antenna
     if(options.antenna):
        self.u.set_antenna(options.antenna, 0)
\endcode

Frequently, your application may need a sample rate that is not
supported by the UHD device. If you have extra CPU power to spare, you
can easily set the sample rate you want, then ask the device what the
actual sample rate set was. Then, you can easily create an arbitrary
resampler to take care of the difference.

\code
    self.u.set_samp_rate(options.samp_rate)

    desired_rate = options.samp_rate
    actual_rate = self.u.get_samp_rate()
    resample = desired_rate / actual_rate

    # Use the blks2 version and pass only the resample factor.
    # This block builds a half-band filter for you

    self.resampler = blks2.pfb_arb_resampler_ccf(resample)
\endcode

*/