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Re: [Discuss-gnuradio] USRP decimation range change while upgrading fro

From: Sebastiaan Heunis
Subject: Re: [Discuss-gnuradio] USRP decimation range change while upgrading from gnuradio 3.1.2 to 3.2.2
Date: Thu, 20 Aug 2009 00:44:29 +0200

Hi Todd

I had a look at convig.vh which determines what gets included with
different fpga firmware builds.  It seems as if the 4 receiver, 0
transmitter version only uses CIC filters and no halfband filters
which explains why you should only be able to decimate by 128.

I don't know what happened previously where you decimated by 250.  The
low level C code which writes the FPGA registers checks whether the
build includes HB filters.  If there are some, you are able to
decimate by up to 256.  If there aren't any, an exception should be
thrown when the decimation rate is above 128.  In your case this
didn't happen.  This is all I know about your problem.  Hopefully it
helps a bit.  This from usrp_standard.cc:

usrp_standard_rx::set_decim_rate(unsigned int rate)
  if (has_rx_halfband()){
    if ((rate & 0x1) || rate < 4 || rate > 256){
      fprintf (stderr, "usrp_standard_rx::set_decim_rate: rate must be
EVEN and in [4, 256]\n");
      return false;
  else {
    if (rate < 4 || rate > 128){
      fprintf (stderr, "usrp_standard_rx::set_decim_rate: rate must be
in [4, 128]\n");
      return false;


Sebastiaan Heunis
Radar Remote Sensing Group, University of Cape Town, South Africa
Tel:  +27 83 305 5667

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