From c85cab2dae0ed59e244a2160fa632596c9707eb9 Mon Sep 17 00:00:00 2001 From: Kyle Keen Date: Tue, 29 Jan 2013 21:38:27 -0500 Subject: =?UTF-8?q?rtl=5Ffm:=20Miroslav=20Sluge=C5=88's=20atan=20lut?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Signed-off-by: Steve Markgraf --- src/rtl_fm.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 75 insertions(+), 7 deletions(-) (limited to 'src/rtl_fm.c') diff --git a/src/rtl_fm.c b/src/rtl_fm.c index 45f8e06..8009876 100644 --- a/src/rtl_fm.c +++ b/src/rtl_fm.c @@ -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< 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) { + 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]); - } else { - pcm = polar_discriminant(fm->signal[i], 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; -- cgit v1.2.3