mirror of
https://github.com/rtlsdrblog/rtl-sdr-blog.git
synced 2025-01-27 10:24:55 +01:00
rtl_fm: add experimental options
Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Kyle Keen
Steve Markgraf
parent
d2f8faa204
commit
374abaebb8
133
src/rtl_fm.c
133
src/rtl_fm.c
@ -29,6 +29,9 @@
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* in-place array operations
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* wide band support
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* sanity checks
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* nicer FIR than square
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* (tried this, was twice as slow and did not sound much better)
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* scale squelch to other input parameters
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*/
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#include <errno.h>
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@ -69,7 +72,8 @@ struct fm_state
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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 downsample; /* min 1, max 256 */
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int post_downsample;
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int output_scale;
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int squelch_level;
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int squelch_hits;
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@ -84,6 +88,10 @@ struct fm_state
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int freq_len;
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int freq_now;
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uint32_t sample_rate;
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int fir_enable;
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int fir[256]; /* fir_len == downsample */
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int fir_sum;
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int custom_atan;
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};
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void usage(void)
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@ -96,13 +104,17 @@ void usage(void)
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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 (use multiple -f for scanning !!BROKEN!!)\n"
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"\t (use multiple -f for scanning)\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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"\t[-l squelch_level (default: 150)]\n"
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"\t[-E freq sets lower edge (default: center)]\n"
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"\tfilename (a '-' dumps samples to stdout)\n\n"
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"Experimental quality/cpu options:\n"
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"\t[-o oversampling (default: 1) !!BROKEN!!]\n"
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"\t[-F enables high quality FIR (default: off/square)]\n"
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"\t[-A enables high speed arctan (default: off)]\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 -V1 -\n\n");
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#endif
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@ -152,8 +164,8 @@ void rotate_90(unsigned char *buf, uint32_t len)
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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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/* simple square window FIR */
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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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@ -173,6 +185,63 @@ void low_pass(struct fm_state *fm, unsigned char *buf, uint32_t len)
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fm->signal_len = i2;
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}
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void build_fir(struct fm_state *fm)
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/* for now, a simple triangle
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* fancy FIRs are equally expensive, so use one */
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/* point = sum(sample[i] * fir[i] * fir_len / fir_sum) */
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{
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int i, len;
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len = fm->downsample;
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for(i = 0; i < len; i++) {
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fm->fir[i] = i;
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}
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for(i = len-1; i <= 0; i--) {
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fm->fir[i] = len - i;
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}
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fm->fir_sum = 0;
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for(i = 0; i < len; i++) {
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fm->fir_sum += fm->fir[i];
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}
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}
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void low_pass_fir(struct fm_state *fm, unsigned char *buf, uint32_t len)
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/* perform an arbitrary FIR, doubles CPU use */
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// possibly bugged, or overflowing
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{
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int i=0, i2=0, i3=0;
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while (i < (int)len) {
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fm->prev_index++;
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i3 = fm->prev_index;
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fm->now_r += ((int)buf[i] - 128) * fm->fir[i3] * fm->downsample / fm->fir_sum;
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fm->now_j += ((int)buf[i+1] - 128) * fm->fir[i3] * fm->downsample / fm->fir_sum;
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i += 2;
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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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int low_pass_simple(int16_t *signal2, int len, int step)
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// no wrap around, length must be multiple of step
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{
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int i, i2, sum;
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for(i=0; i < len; i+=step) {
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sum = 0;
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for(i2=0; i2<step; i2++) {
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sum += (int)signal2[i + i2];
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}
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signal2[i] = (int16_t)(sum / step);
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}
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return len / step;
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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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@ -182,10 +251,22 @@ void multiply(int ar, int aj, int br, int bj, int *cr, int *cj)
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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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angle = atan2((double)cj, (double)cr);
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//if (angle > (3.14159) || angle < (-3.14159))
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// {fprintf(stderr, "overflow %f\n", angle);}
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return (int)(angle / 3.14159 * (1<<14));
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}
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int fast_atan2(int y, int x)
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/* pre scaled for int16 */
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{
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int yabs, angle, pi4=(1<<12); // note pi = 1<<14
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int yabs, angle;
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int pi4=(1<<12), pi34=3*(1<<12); // note pi = 1<<14
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if (x==0 && y==0) {
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return 0;
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}
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@ -196,7 +277,7 @@ int fast_atan2(int y, int x)
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if (x >= 0) {
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angle = pi4 - pi4 * (x-yabs) / (x+yabs);
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} else {
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angle = 3*pi4 - pi4 * (x+yabs) / (yabs-x);
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angle = pi34 - pi4 * (x+yabs) / (yabs-x);
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}
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if (y < 0) {
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return -angle;
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@ -204,14 +285,11 @@ int fast_atan2(int y, int x)
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return angle;
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}
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int polar_discriminant(int ar, int aj, int br, int bj)
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int polar_disc_fast(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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angle = atan2((double)cj, (double)cr);
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return (int)(angle / 3.14159 * (1<<14));
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//return fast_atan2(cj, cr);
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return fast_atan2(cj, cr);
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}
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void fm_demod(struct fm_state *fm)
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@ -221,8 +299,13 @@ void fm_demod(struct fm_state *fm)
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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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if (fm->custom_atan) {
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pcm = polar_disc_fast(fm->signal[i], fm->signal[i+1],
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fm->signal[i-2], fm->signal[i-1]);
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} else {
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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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}
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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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@ -281,13 +364,17 @@ static void optimal_settings(struct fm_state *fm, int freq, int hopping)
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r = rtlsdr_set_center_freq(dev, (uint32_t)capture_freq);
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if (hopping) {
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return;}
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fprintf(stderr, "Oversampling by: %ix.\n", fm->downsample);
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fprintf(stderr, "Oversampling input by: %ix.\n", fm->downsample);
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fprintf(stderr, "Oversampling output by: %ix.\n", fm->post_downsample);
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fprintf(stderr, "Buffer size: %0.2fms\n",
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1000 * 0.5 * (float)DEFAULT_BUF_LENGTH / (float)capture_rate);
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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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/* Set the sample rate */
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fprintf(stderr, "Sampling at %u Hz.\n", capture_rate);
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r = rtlsdr_set_sample_rate(dev, (uint32_t)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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@ -298,9 +385,15 @@ void full_demod(unsigned char *buf, uint32_t len, struct fm_state *fm)
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{
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int sr, freq_next;
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rotate_90(buf, len);
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if (fm->fir_enable) {
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low_pass_fir(fm, buf, len);
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} else {
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low_pass(fm, buf, len);
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}
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fm_demod(fm);
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sr = post_squelch(fm);
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if (fm->post_downsample > 1) {
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fm->signal_len = low_pass_simple(fm->signal2, fm->signal_len, fm->post_downsample);}
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/* ignore under runs for now */
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fwrite(fm->signal2, 2, fm->signal_len/2, fm->file);
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if (fm->freq_len > 1 && !sr && fm->squelch_hits > CONSEQ_SQUELCH) {
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@ -362,9 +455,13 @@ int main(int argc, char **argv)
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fm.squelch_level = 150;
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fm.freq_len = 0;
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fm.edge = 0;
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fm.fir_enable = 0;
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fm.prev_index = -1;
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fm.post_downsample = 1;
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fm.custom_atan = 0;
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sem_init(&data_ready, 0, 0);
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#ifndef _WIN32
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while ((opt = getopt(argc, argv, "d:f:g:s:b:l:E::")) != -1) {
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while ((opt = getopt(argc, argv, "d:f:g:s:b:l:o:EFA")) != -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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@ -382,14 +479,25 @@ int main(int argc, char **argv)
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case 's':
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fm.sample_rate = (uint32_t)atof(optarg);
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break;
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case 'o':
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fm.post_downsample = (int)atof(optarg);
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break;
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case 'E':
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fm.edge = 1;
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break;
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case 'F':
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fm.fir_enable = 1;
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break;
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case 'A':
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fm.custom_atan = 1;
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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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/* double sample_rate to limit to Δθ to ±π */
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fm.sample_rate *= fm.post_downsample;
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if (argc <= optind) {
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usage();
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@ -443,6 +551,7 @@ int main(int argc, char **argv)
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#endif
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optimal_settings(&fm, 0, 0);
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build_fir(&fm);
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/* Set the tuner gain */
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r = rtlsdr_set_tuner_gain(dev, gain);
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