mirror of
https://github.com/rtlsdrblog/rtl-sdr-blog.git
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rtl_fm: prototype FM demod
Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Kyle Keen
Steve Markgraf
parent
9d0232385b
commit
6328e11da6
361
src/rtl_fm.c
Normal file
361
src/rtl_fm.c
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@ -0,0 +1,361 @@
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/*
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* rtl-sdr, turns your Realtek RTL2832 based DVB dongle into a SDR receiver
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* Copyright (C) 2012 by Steve Markgraf <steve@steve-m.de>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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* written because people could not do real time
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* FM demod on Atom hardware with GNU radio
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* based on rtl_sdr.c
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* todo: realtime ARMv5
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* remove float math (disqualifies complex.h)
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* replace atan2 with a fast approximation
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* in-place array operations
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* wide band support
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* squelch
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* better threading
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*/
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#include <errno.h>
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#include <signal.h>
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#include <string.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#ifndef _WIN32
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#include <unistd.h>
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#else
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#include <Windows.h>
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#endif
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#include "rtl-sdr.h"
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#define DEFAULT_SAMPLE_RATE 24000
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#define DEFAULT_ASYNC_BUF_NUMBER 32
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#define DEFAULT_BUF_LENGTH 1024
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#define MINIMAL_BUF_LENGTH 512
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#define MAXIMAL_BUF_LENGTH (256 * 16384)
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static int do_exit = 0;
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static rtlsdr_dev_t *dev = NULL;
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struct fm_state
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{
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int now_r;
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int now_j;
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int pre_r;
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int pre_j;
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int prev_index;
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int downsample; /* min 4, max 256 */
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int output_scale;
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int signal[2048]; /* 16 bit signed i/q pairs */
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int16_t signal2[2048]; /* signal has lowpass, signal2 has demod */
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int signal_len;
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FILE *file;
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};
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void usage(void)
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{
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#ifdef _WIN32
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fprintf(stderr,"rtl_fm, a simple FM demodulator for RTL2832 based USB-sticks\n\n"
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"Usage:\t rtl_fm-win.exe [device_index] [samplerate in kHz] "
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"[gain] [frequency in Hz] [filename]\n");
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#else
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fprintf(stderr,
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"rtl_fm, a simple narrow band FM demodulator for RTL2832 based DVB-T receivers\n\n"
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"Usage:\t -f frequency_to_tune_to [Hz]\n"
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"\t[-s samplerate (default: 24000 Hz)]\n"
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"\t[-d device_index (default: 0)]\n"
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"\t[-g tuner_gain (default: -1dB)]\n"
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"\tfilename (a '-' dumps samples to stdout)\n\n"
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"Produces signed 16 bit ints, use sox to hear them.\n"
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"\trtl_fm ... | play -t raw -r 24k -e signed-integer -b 16 -c 1 -\n\n");
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#endif
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exit(1);
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}
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#ifdef _WIN32
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BOOL WINAPI
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sighandler(int signum)
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{
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if (CTRL_C_EVENT == signum) {
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fprintf(stderr, "Signal caught, exiting!\n");
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do_exit = 1;
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rtlsdr_cancel_async(dev);
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return TRUE;
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}
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return FALSE;
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}
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#else
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static void sighandler(int signum)
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{
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fprintf(stderr, "Signal caught, exiting!\n");
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do_exit = 1;
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rtlsdr_cancel_async(dev);
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}
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#endif
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void rotate_90(unsigned char *buf, uint32_t len)
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/* 90 rotation is 1+0j, 0+1j, -1+0j, 0-1j
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or [0, 1, -3, 2, -4, -5, 7, -6] */
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{
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uint32_t i;
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unsigned char tmp;
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for (i=0; i<len; i+=8)
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{
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/* uint_8 negation = 255 - x */
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tmp = 255 - buf[i+3];
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buf[i+3] = buf[i+2];
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buf[i+2] = tmp;
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buf[i+4] = 255 - buf[i+4];
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buf[i+5] = 255 - buf[i+5];
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tmp = 255 - buf[i+6];
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buf[i+6] = buf[i+7];
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buf[i+7] = tmp;
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}
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}
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void low_pass(struct fm_state *fm, unsigned char *buf, uint32_t len)
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{
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/* simple square window FIR */
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int i=0, i2=0;
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while (i < (int)len) {
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fm->now_r += ((int)buf[i] - 128);
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fm->now_j += ((int)buf[i+1] - 128);
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i += 2;
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fm->prev_index++;
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if (fm->prev_index < (fm->downsample)) {
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continue;
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}
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fm->signal[i2] = fm->now_r * fm->output_scale;
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fm->signal[i2+1] = fm->now_j * fm->output_scale;
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fm->prev_index = -1;
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fm->now_r = 0;
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fm->now_j = 0;
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i2 += 2;
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}
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fm->signal_len = i2;
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}
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/* define our own complex math ops
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because ARMv5 has no hardware float */
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void multiply(int ar, int aj, int br, int bj, int *cr, int *cj)
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{
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*cr = ar*br - aj*bj;
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*cj = aj*br + ar*bj;
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}
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int polar_discriminant(int ar, int aj, int br, int bj)
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{
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int cr, cj;
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double angle;
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multiply(ar, aj, br, -bj, &cr, &cj);
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/* fake squelch */
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//if (abs(cr) + abs(cj) < 50000)
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// {return 0;}
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angle = atan2((double)cj, (double)cr);
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return (int)(angle / 3.14159 * (1<<14));
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}
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void fm_demod(struct fm_state *fm)
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{
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int i, pcm;
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pcm = polar_discriminant(fm->signal[0], fm->signal[1],
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fm->pre_r, fm->pre_j);
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fm->signal2[0] = (int16_t)pcm;
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for (i = 2; i < (fm->signal_len); i += 2) {
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pcm = polar_discriminant(fm->signal[i], fm->signal[i+1],
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fm->signal[i-2], fm->signal[i-1]);
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fm->signal2[i/2] = (int16_t)pcm;
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}
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fm->pre_r = fm->signal[fm->signal_len - 2];
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fm->pre_j = fm->signal[fm->signal_len - 1];
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}
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static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx)
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{
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struct fm_state *fm2;
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if (!ctx) {
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return;
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}
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fm2 = (struct fm_struct*)(ctx); // bad conversion?
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rotate_90(buf, len);
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low_pass(fm2, buf, len);
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fm_demod(fm2);
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/* ignore under runs for now */
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fwrite(fm2->signal2, 2, fm2->signal_len/2, fm2->file);
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}
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static void optimal_settings(struct fm_state *fm, int freq, int rate)
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{
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int r, capture_freq, capture_rate;
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fm->downsample = (1000000 / rate) + 1;
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fprintf(stderr, "Oversampling by: %ix.\n", fm->downsample);
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capture_rate = fm->downsample * rate;
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capture_freq = freq + capture_rate/4;
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fm->output_scale = (1<<15) / (128 * fm->downsample);
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if (fm->output_scale < 1) {
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fm->output_scale = 1;
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}
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fm->output_scale = 1;
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/* Set the sample rate */
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r = rtlsdr_set_sample_rate(dev, capture_rate);
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if (r < 0)
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fprintf(stderr, "WARNING: Failed to set sample rate.\n");
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/* Set the frequency */
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r = rtlsdr_set_center_freq(dev, capture_freq);
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if (r < 0)
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fprintf(stderr, "WARNING: Failed to set center freq.\n");
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else
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fprintf(stderr, "Tuned to %u Hz.\n", capture_freq);
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}
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int main(int argc, char **argv)
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{
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#ifndef _WIN32
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struct sigaction sigact;
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#endif
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struct fm_state fm;
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char *filename = NULL;
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int n_read;
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int r, opt;
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int i, gain = -10; // tenths of a dB
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uint8_t *buffer;
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uint32_t dev_index = 0;
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uint32_t frequency = 100000000;
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uint32_t samp_rate = DEFAULT_SAMPLE_RATE;
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uint32_t out_block_size = DEFAULT_BUF_LENGTH;
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int device_count;
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char vendor[256], product[256], serial[256];
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#ifndef _WIN32
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while ((opt = getopt(argc, argv, "d:f:g:s:b:S::")) != -1) {
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switch (opt) {
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case 'd':
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dev_index = atoi(optarg);
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break;
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case 'f':
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frequency = (uint32_t)atof(optarg);
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break;
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case 'g':
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gain = (int)(atof(optarg) * 10);
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break;
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case 's':
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samp_rate = (uint32_t)atof(optarg);
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break;
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default:
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usage();
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break;
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}
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}
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if (argc <= optind) {
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usage();
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} else {
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filename = argv[optind];
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}
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#else
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if(argc <6)
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usage();
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dev_index = atoi(argv[1]);
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samp_rate = atoi(argv[2])*1000;
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gain=(int)(atof(argv[3]) * 10);
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frequency = atoi(argv[4]);
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filename = argv[5];
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#endif
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out_block_size = DEFAULT_BUF_LENGTH;
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buffer = malloc(out_block_size * sizeof(uint8_t));
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device_count = rtlsdr_get_device_count();
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if (!device_count) {
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fprintf(stderr, "No supported devices found.\n");
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exit(1);
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}
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fprintf(stderr, "Found %d device(s):\n", device_count);
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for (i = 0; i < device_count; i++) {
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rtlsdr_get_device_usb_strings(i, vendor, product, serial);
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fprintf(stderr, " %d: %s, %s, SN: %s\n", i, vendor, product, serial);
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}
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fprintf(stderr, "\n");
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fprintf(stderr, "Using device %d: %s\n",
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dev_index, rtlsdr_get_device_name(dev_index));
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r = rtlsdr_open(&dev, dev_index);
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if (r < 0) {
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fprintf(stderr, "Failed to open rtlsdr device #%d.\n", dev_index);
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exit(1);
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}
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#ifndef _WIN32
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sigact.sa_handler = sighandler;
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sigemptyset(&sigact.sa_mask);
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sigact.sa_flags = 0;
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sigaction(SIGINT, &sigact, NULL);
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sigaction(SIGTERM, &sigact, NULL);
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sigaction(SIGQUIT, &sigact, NULL);
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sigaction(SIGPIPE, &sigact, NULL);
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#else
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SetConsoleCtrlHandler( (PHANDLER_ROUTINE) sighandler, TRUE );
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#endif
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optimal_settings(&fm, frequency, samp_rate);
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/* Set the tuner gain */
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r = rtlsdr_set_tuner_gain(dev, gain);
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if (r < 0)
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fprintf(stderr, "WARNING: Failed to set tuner gain.\n");
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else
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fprintf(stderr, "Tuner gain set to %0.2f dB.\n", gain/10.0);
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if(strcmp(filename, "-") == 0) { /* Write samples to stdout */
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fm.file = stdout;
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} else {
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fm.file = fopen(filename, "wb");
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if (!fm.file) {
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fprintf(stderr, "Failed to open %s\n", filename);
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goto out;
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}
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}
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/* Reset endpoint before we start reading from it (mandatory) */
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r = rtlsdr_reset_buffer(dev);
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if (r < 0)
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fprintf(stderr, "WARNING: Failed to reset buffers.\n");
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fprintf(stderr, "Reading samples in async mode...\n");
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r = rtlsdr_read_async(dev, rtlsdr_callback, (void *)(&fm),
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DEFAULT_ASYNC_BUF_NUMBER, out_block_size);
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if (do_exit)
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fprintf(stderr, "\nUser cancel, exiting...\n");
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else
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fprintf(stderr, "\nLibrary error %d, exiting...\n", r);
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if (fm.file != stdout)
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fclose(fm.file);
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rtlsdr_close(dev);
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free (buffer);
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out:
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return r >= 0 ? r : -r;
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}
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