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rtl_fm: set nearest gain 

Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Kyle Keen 2013-09-07 18:26:10 -04:00 committed by Steve Markgraf
parent 31cef2ef55
commit b70720b9b6
1 changed files with 48 additions and 12 deletions
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60
src/rtl_fm.c
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@ -32,13 +32,15 @@
* scale squelch to other input parameters
* test all the demodulations
* pad output on hop
* nearest gain approx
* frequency ranges could be stored better
* scaled AM demod amplification
* auto-hop after time limit
* peak detector to tune onto stronger signals
* use slower sample rates (250k) for nbfm
* offset tuning
* fifo for active hop frequency
* clips
* real squelch math
*/
#include <errno.h>
@ -150,10 +152,16 @@ void usage(void)
"\t[-U enables USB mode (default: off)]\n"
//"\t[-D enables DSB mode (default: off)]\n"
"\t[-R enables raw mode (default: off, 2x16 bit output)]\n"
"\t[-F enables high quality FIR (default: off/square)]\n"
"\t[-F enables Hamming FIR (default: off/square)]\n"
"\t[-D enables de-emphasis (default: off)]\n"
"\t[-C enables DC blocking of output (default: off)]\n"
"\t[-A std/fast/lut choose atan math (default: std)]\n\n"
"\t[-A std/fast/lut choose atan math (default: std)]\n"
//"\t[-C clip_path (default: off)\n"
//"\t (create time stamped raw clips, requires squelch)\n"
//"\t (path must have '\%s' and will expand to date_time_freq)\n"
//"\t[-H hop_fifo (default: off)\n"
//"\t (fifo will contain the active frequency)\n"
"\n"
"Produces signed 16 bit ints, use Sox or aplay to hear them.\n"
"\trtl_fm ... - | play -t raw -r 24k -es -b 16 -c 1 -V1 -\n"
"\t | aplay -r 24k -f S16_LE -t raw -c 1\n"
@ -230,17 +238,18 @@ void low_pass(struct fm_state *fm, unsigned char *buf, uint32_t len)
}
void build_fir(struct fm_state *fm)
/* for now, a simple triangle
* fancy FIRs are equally expensive, so use one */
/* hamming */
/* point = sum(sample[i] * fir[i] * fir_len / fir_sum) */
{
double a, b, w, N1;
int i, len;
len = fm->downsample;
for(i = 0; i < (len/2); i++) {
fm->fir[i] = i;
}
for(i = len-1; i >= (len/2); i--) {
fm->fir[i] = len - i;
a = 25.0/46.0;
b = 21.0/46.0;
N1 = (double)(len-1);
for(i = 0; i < len; i++) {
w = a - b*cos(2*i*M_PI/N1);
fm->fir[i] = (int)(w * 255);
}
fm->fir_sum = 0;
for(i = 0; i < len; i++) {
@ -255,13 +264,17 @@ void low_pass_fir(struct fm_state *fm, unsigned char *buf, uint32_t len)
int i=0, i2=0, i3=0;
while (i < (int)len) {
i3 = fm->prev_index;
fm->now_r += ((int)buf[i] - 127) * fm->fir[i3] * fm->downsample / fm->fir_sum;
fm->now_j += ((int)buf[i+1] - 127) * fm->fir[i3] * fm->downsample / fm->fir_sum;
fm->now_r += ((int)buf[i] - 127) * fm->fir[i3];
fm->now_j += ((int)buf[i+1] - 127) * fm->fir[i3];
i += 2;
fm->prev_index++;
if (fm->prev_index < fm->downsample) {
continue;
}
fm->now_r *= fm->downsample;
fm->now_j *= fm->downsample;
fm->now_r /= fm->fir_sum;
fm->now_j /= fm->fir_sum;
fm->signal[i2] = fm->now_r; //* fm->output_scale;
fm->signal[i2+1] = fm->now_j; //* fm->output_scale;
fm->prev_index = 0;
@ -730,6 +743,28 @@ void frequency_range(struct fm_state *fm, char *arg)
step[-1] = ':';
}
int nearest_gain(int target_gain)
{
int i, err1, err2, count, close_gain;
int* gains;
count = rtlsdr_get_tuner_gains(dev, NULL);
if (count <= 0) {
return 0;
}
gains = malloc(sizeof(int) * count);
count = rtlsdr_get_tuner_gains(dev, gains);
close_gain = gains[0];
for (i=0; i<count; i++) {
err1 = abs(target_gain - close_gain);
err2 = abs(target_gain - gains[i]);
if (err2 < err1) {
close_gain = gains[i];
}
}
free(gains);
return close_gain;
}
void fm_init(struct fm_state *fm)
{
fm->freqs[0] = 100000000;
@ -952,6 +987,7 @@ int main(int argc, char **argv)
r = rtlsdr_set_tuner_gain_mode(dev, 0);
} else {
r = rtlsdr_set_tuner_gain_mode(dev, 1);
gain = nearest_gain(gain);
r = rtlsdr_set_tuner_gain(dev, gain);
}
if (r != 0) {