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rtl_fm: Miroslav Slugeň's atan lut 

Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Kyle Keen 2013-01-29 21:38:27 -05:00 committed by Steve Markgraf
parent c6a731a0dc
commit c85cab2dae
1 changed files with 76 additions and 8 deletions
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84
src/rtl_fm.c
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@ -72,6 +72,10 @@ static int do_exit = 0;
static rtlsdr_dev_t *dev = NULL;
static int lcm_post[17] = {1,1,1,3,1,5,3,7,1,9,5,11,3,13,7,15,1};
static int *atan_lut = NULL;
static int atan_lut_size = 131072; /* 512 KB */
static int atan_lut_coef = 8;
struct fm_state
{
int now_r;
@ -128,7 +132,7 @@ void usage(void)
"\t[-E sets lower edge tuning (default: center)]\n"
"\t[-N enables NBFM mode (default: on)]\n"
"\t[-W enables WBFM mode (default: off)]\n"
"\t (-N -s 170k -o 4 -A -r 32k -l 0 -D)\n"
"\t (-N -s 170k -o 4 -A fast -r 32k -l 0 -D)\n"
"\tfilename (a '-' dumps samples to stdout)\n"
"\t (omitting the filename also uses stdout)\n\n"
"Experimental options:\n"
@ -142,7 +146,7 @@ void usage(void)
"\t[-R enables raw mode (default: off, 2x16 bit output)]\n"
"\t[-F enables high quality FIR (default: off/square)]\n"
"\t[-D enables de-emphasis (default: off)]\n"
"\t[-A enables high speed arctan (default: off)]\n\n"
"\t[-A std/fast/lut choose atan math (default: std)]\n\n"
"Produces signed 16 bit ints, use Sox or aplay to hear them.\n"
"\trtl_fm ... - | play -t raw -r 24k -e signed-integer -b 16 -c 1 -V1 -\n"
"\t | aplay -r 24k -f S16_LE -t raw -c 1\n"
@ -343,6 +347,57 @@ int polar_disc_fast(int ar, int aj, int br, int bj)
return fast_atan2(cj, cr);
}
int atan_lut_init()
{
int i = 0;
atan_lut = malloc(atan_lut_size * sizeof(int));
for (i = 0; i < atan_lut_size; i++) {
atan_lut[i] = (int) (atan((double) i / (1<<atan_lut_coef)) / 3.14159 * (1<<14));
}
return 0;
}
int polar_disc_lut(int ar, int aj, int br, int bj)
{
int cr, cj, x, x_abs;
multiply(ar, aj, br, -bj, &cr, &cj);
/* special cases */
if (cr == 0 || cj == 0) {
if (cr == 0 && cj == 0)
{return 0;}
if (cr == 0 && cj > 0)
{return 1 << 13;}
if (cr == 0 && cj < 0)
{return -(1 << 13);}
if (cj == 0 && cr > 0)
{return 0;}
if (cj == 0 && cr < 0)
{return 1 << 14;}
}
/* real range -32768 - 32768 use 64x range -> absolute maximum: 2097152 */
x = (cj << atan_lut_coef) / cr;
x_abs = abs(x);
if (x_abs >= atan_lut_size) {
/* we can use linear range, but it is not necessary */
return (cj > 0) ? 1<<13 : -1<<13;
}
if (x > 0) {
return (cj > 0) ? atan_lut[x] : atan_lut[x] - (1<<14);
} else {
return (cj > 0) ? (1<<14) - atan_lut[-x] : -atan_lut[-x];
}
return 0;
}
void fm_demod(struct fm_state *fm)
{
int i, pcm;
@ -350,12 +405,19 @@ void fm_demod(struct fm_state *fm)
fm->pre_r, fm->pre_j);
fm->signal2[0] = (int16_t)pcm;
for (i = 2; i < (fm->signal_len); i += 2) {
if (fm->custom_atan) {
pcm = polar_disc_fast(fm->signal[i], fm->signal[i+1],
fm->signal[i-2], fm->signal[i-1]);
} else {
switch (fm->custom_atan) {
case 0:
pcm = polar_discriminant(fm->signal[i], fm->signal[i+1],
fm->signal[i-2], fm->signal[i-1]);
break;
case 1:
pcm = polar_disc_fast(fm->signal[i], fm->signal[i+1],
fm->signal[i-2], fm->signal[i-1]);
break;
case 2:
pcm = polar_disc_lut(fm->signal[i], fm->signal[i+1],
fm->signal[i-2], fm->signal[i-1]);
break;
}
fm->signal2[i/2] = (int16_t)pcm;
}
@ -640,7 +702,7 @@ int main(int argc, char **argv)
fm.mode_demod = &fm_demod;
sem_init(&data_ready, 0, 0);
while ((opt = getopt(argc, argv, "d:f:g:s:b:l:o:t:r:p:EFANWMULRD")) != -1) {
while ((opt = getopt(argc, argv, "d:f:g:s:b:l:o:t:r:p:EFA:NWMULRD")) != -1) {
switch (opt) {
case 'd':
dev_index = atoi(optarg);
@ -688,7 +750,13 @@ int main(int argc, char **argv)
fm.fir_enable = 1;
break;
case 'A':
fm.custom_atan = 1;
if (strcmp("std", optarg) == 0) {
fm.custom_atan = 0;}
if (strcmp("fast", optarg) == 0) {
fm.custom_atan = 1;}
if (strcmp("lut", optarg) == 0) {
atan_lut_init();
fm.custom_atan = 2;}
break;
case 'D':
fm.deemph = 1;