I'm trying to capture some over-the-air data using a USRP and a RFX2400 card. Using usrp_fft.py or usrp_rx_cfile.py works fine as long as the decimation rate is 8 or above. Unfortunately my signal has a 10MHz bandwidth, so I would like to use a decimation rate of 4 (16Msps I&Q). This results in overflows due to the USB rate. It seems that the normal solution for this is to enable 8 bit samples. Both usrp_fft.py and usrp_rx_cfile.py have a "-8" option, however when I use that option the data is all zeroes.
So, I snooped around and found a C++ file by Firas Abbas Hamza that removed the python hocus pocus and talked to the usrp library directly. Same problem - works fine as long as the 8 bit sample transfer is not enabled.
I also tried this with a DBSRX daughter card (and an appropriate frequency). Same problem.
Has anyone had any luck using 8 bit sample mode lately? I've included theC++ file below (Note: had to modify it to use shared pointers).
Thanks, Mike
// Simple C++ USRP interfacing demonstration program // // // This program modified from C++ code found in document: // The USRP under 1.5X Magnifying Lens! // By:
// Firas Abbas Hamza // Rev 1.0 // Last updated: 12-Jun-2008
// This program was derived and modified from test_usrp_standard_rx.cc /* -*- c++ -*- */ /* * Copyright 2003,2006,2007,2008 Free Software Foundation, Inc.
* * This file is part of GNU Radio * * GNU Radio is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 3, or (at your option)
* any later version. * * GNU Radio is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with GNU Radio; see the file COPYING. If not, write to * the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA. */ #include <stdlib.h> #include <stdio.h> #include "usrp_standard.h"
#define SAMPLES_PER_READ (512) // Must be a multiple of 128
// Dumy Function to process USRP data void process_data(int *buffer) { int i; int max = 0; for (i = 0; i < SAMPLES_PER_READ; i++) { if (buffer[i] > max) { max = buffer[i];
} } printf("max: %d\n", max); }
int main (int argc, char **argv) { bool width_8_p = true; int which_board = 0; int decim = 64; double center_freq = 2647000000;
int fusb_block_size = 0; int fusb_nblocks = 0; int nchannels = 1; int gain = 0; int mode = 0; int noverruns = 0; bool overrun; int total_reads = 10000;
int i; int buf[SAMPLES_PER_READ]; int bufsize = SAMPLES_PER_READ*4;
usrp_standard_rx_sptr urx = usrp_standard_rx::make (which_board, decim, 1, -1, mode, fusb_block_size, fusb_nblocks, "std_4rx_0tx.rbf"); if (urx == 0) { fprintf (stderr, "Error: usrp_standard_rx::make\n");
exit (1); } if (width_8_p) { int width = 8; int shift = 8; bool want_q = true; if (!urx->set_format(usrp_standard_rx::make_format(width, shift, want_q, true)))
{ fprintf (stderr, "Error: urx->set_format\n"); exit (1); } } // Set DDC center frequency urx->set_rx_freq (0, center_freq); // Set Number of channels
urx->set_nchannels(1); // Set ADC PGA gain urx->set_pga(0,gain); // Set FPGA Mux urx->set_mux(0x32103210); // Board A only // Set DDC decimation rate urx->set_decim_rate(decim);
// Set DDC phase urx->set_ddc_phase(0,0); urx->start(); // Start data transfer printf("USRP Transfer Started\n"); // Do USRP Samples Reading for (i = 0; i < total_reads; i++)
{ urx->read(&buf, bufsize, &overrun); if (overrun) { printf ("USRP Rx Overrun\n"); noverruns++;
} // Do whatever you want with the data process_data(&buf[0]); } urx->stop(); // Stop data transfer printf("USRP Transfer Stoped\n");
// delete urx; return 0; }