aboutsummaryrefslogtreecommitdiffstats
path: root/src/rtl_fm.c
diff options
context:
space:
mode:
authorKyle Keen <keenerd@gmail.com>2013-09-07 18:26:10 -0400
committerSteve Markgraf <steve@steve-m.de>2013-10-24 23:29:46 +0200
commitb70720b9b622996afc5dbbd9abc61fa2d757081d (patch)
treea20cb19f12eb6fc0194b36df0cf3bcae8a8f76f1 /src/rtl_fm.c
parent31cef2ef5525da9d2ae306a1515475b6f5c17ef0 (diff)
rtl_fm: set nearest gain
Signed-off-by: Steve Markgraf <steve@steve-m.de>
Diffstat (limited to 'src/rtl_fm.c')
-rw-r--r--src/rtl_fm.c60
1 files changed, 48 insertions, 12 deletions
diff --git a/src/rtl_fm.c b/src/rtl_fm.c
index 0d23fdc..1acdfde 100644
--- a/src/rtl_fm.c
+++ b/src/rtl_fm.c
@@ -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) {