From 6dcc8baad448d000ef355abc6d9abf7a3490a800 Mon Sep 17 00:00:00 2001 From: Andreas Eversberg Date: Sun, 1 Sep 2019 15:38:16 +0200 Subject: Split FSK modem code into separate modulator and demodulator --- src/libfsk/fsk.c | 232 ++++++++++++++++++++++++++++++++----------------------- src/libfsk/fsk.h | 32 +++++--- 2 files changed, 158 insertions(+), 106 deletions(-) (limited to 'src/libfsk') diff --git a/src/libfsk/fsk.c b/src/libfsk/fsk.c index 6b5fe03..7f1ed6e 100644 --- a/src/libfsk/fsk.c +++ b/src/libfsk/fsk.c @@ -33,21 +33,18 @@ * fsk = instance of fsk modem * inst = instance of user * send_bit() = function to be called whenever a new bit has to be sent - * receive_bit() = function to be called whenever a new bit was received * samplerate = samplerate * bitrate = bits per second * f0, f1 = two frequencies for bit 0 and bit 1 * level = level to modulate the frequencies * coherent = use coherent modulation (FFSK) - * bitadjust = how much to adjust the sample clock when a bitchange was detected. (0 = nothing, don't use this, 0.5 full adjustment) */ -int fsk_init(fsk_t *fsk, void *inst, int (*send_bit)(void *inst), void (*receive_bit)(void *inst, int bit, double quality, double level), int samplerate, double bitrate, double f0, double f1, double level, int coherent, double bitadjust) +int fsk_mod_init(fsk_mod_t *fsk, void *inst, int (*send_bit)(void *inst), int samplerate, double bitrate, double f0, double f1, double level, int coherent) { - double bandwidth; int i; int rc; - PDEBUG(DDSP, DEBUG_DEBUG, "Setup FSK for Transceiver. (F0 = %.1f, F1 = %.1f, peak = %.1f)\n", f0, f1, level); + PDEBUG(DDSP, DEBUG_DEBUG, "Setup FSK for Transmitter. (F0 = %.1f, F1 = %.1f, peak = %.1f)\n", f0, f1, level); memset(fsk, 0, sizeof(*fsk)); @@ -62,9 +59,6 @@ int fsk_init(fsk_t *fsk, void *inst, int (*send_bit)(void *inst), void (*receive fsk->sin_tab[i] = sin((double)i / 65536.0 * 2.0 * PI) * level; fsk->inst = inst; - fsk->rx_bit = -1; - fsk->rx_bitadjust = bitadjust; - fsk->receive_bit = receive_bit; fsk->tx_bit = -1; fsk->level = level; fsk->send_bit = send_bit; @@ -78,14 +72,6 @@ int fsk_init(fsk_t *fsk, void *inst, int (*send_bit)(void *inst), void (*receive fsk->high_bit = 0; } - /* calculate bandwidth */ - bandwidth = fabs(f0 - f1) * 2.0; - - /* init fm demodulator */ - rc = fm_demod_init(&fsk->demod, (double)samplerate, (f0 + f1) / 2.0, bandwidth); - if (rc < 0) - goto error; - fsk->bits_per_sample = (double)bitrate / (double)samplerate; PDEBUG(DDSP, DEBUG_DEBUG, "Bitduration of %.4f bits per sample @ %d.\n", fsk->bits_per_sample, samplerate); @@ -118,19 +104,150 @@ int fsk_init(fsk_t *fsk, void *inst, int (*send_bit)(void *inst), void (*receive return 0; error: - fsk_cleanup(fsk); + fsk_mod_cleanup(fsk); return rc; } /* Cleanup transceiver instance. */ -void fsk_cleanup(fsk_t *fsk) +void fsk_mod_cleanup(fsk_mod_t *fsk) { - PDEBUG(DDSP, DEBUG_DEBUG, "Cleanup FSK for Transceiver.\n"); + PDEBUG(DDSP, DEBUG_DEBUG, "Cleanup FSK for Transmitter.\n"); if (fsk->sin_tab) { free(fsk->sin_tab); fsk->sin_tab = NULL; } +} + +/* modulate bits + * + * If first/next bit is required, callback function send_bit() is called. + * If there is no (more) data to be transmitted, the callback functions shall + * return -1. In this case, this function stops and returns the number of + * samples that have been rendered so far, if any. + * + * For coherent mode (FSK), we round the phase on every bit change to the + * next zero crossing. This prevents phase shifts due to rounding errors. + */ +int fsk_mod_send(fsk_mod_t *fsk, sample_t *sample, int length, int add) +{ + int count = 0; + double phase, phaseshift; + + phase = fsk->tx_phase65536; + + /* get next bit */ + if (fsk->tx_bit < 0) { +next_bit: + fsk->tx_bit = fsk->send_bit(fsk->inst); +#ifdef DEBUG_MODULATOR + printf("bit change to %d\n", fsk->tx_bit); +#endif + if (fsk->tx_bit < 0) + goto done; + /* correct phase when changing bit */ + if (fsk->coherent) { + /* round phase to nearest zero crossing */ + if (phase > 16384.0 && phase < 49152.0) + phase = 32768.0; + else + phase = 0; + /* set phase according to current position in bit */ + phase += fsk->tx_bitpos * fsk->cycles_per_bit65536[fsk->tx_bit & 1]; +#ifdef DEBUG_MODULATOR + printf("phase %.3f bitpos=%.6f\n", phase, fsk->tx_bitpos); +#endif + } + } + + /* modulate bit */ + phaseshift = fsk->phaseshift65536[fsk->tx_bit & 1]; + while (count < length && fsk->tx_bitpos < 1.0) { + if (add) + sample[count++] += fsk->sin_tab[(uint16_t)phase]; + else + sample[count++] = fsk->sin_tab[(uint16_t)phase]; +#ifdef DEBUG_MODULATOR + printf("|%s|\n", debug_amplitude(fsk->sin_tab[(uint16_t)phase] / fsk->level)); +#endif + phase += phaseshift; + if (phase >= 65536.0) + phase -= 65536.0; + fsk->tx_bitpos += fsk->bits_per_sample; + } + if (fsk->tx_bitpos >= 1.0) { + fsk->tx_bitpos -= 1.0; + goto next_bit; + } + +done: + fsk->tx_phase65536 = phase; + + return count; +} + +/* reset transmitter state, so we get a clean start */ +void fsk_mod_tx_reset(fsk_mod_t *fsk) +{ + fsk->tx_phase65536 = 0; + fsk->tx_bitpos = 0; + fsk->tx_bit = -1; +} + +/* + * fsk = instance of fsk modem + * inst = instance of user + * receive_bit() = function to be called whenever a new bit was received + * samplerate = samplerate + * bitrate = bits per second + * f0, f1 = two frequencies for bit 0 and bit 1 + * bitadjust = how much to adjust the sample clock when a bitchange was detected. (0 = nothing, don't use this, 0.5 full adjustment) + */ +int fsk_demod_init(fsk_demod_t *fsk, void *inst, void (*receive_bit)(void *inst, int bit, double quality, double level), int samplerate, double bitrate, double f0, double f1, double bitadjust) +{ + double bandwidth; + int rc; + + PDEBUG(DDSP, DEBUG_DEBUG, "Setup FSK for Receiver. (F0 = %.1f, F1 = %.1f)\n", f0, f1); + + memset(fsk, 0, sizeof(*fsk)); + + fsk->inst = inst; + fsk->rx_bit = -1; + fsk->rx_bitadjust = bitadjust; + fsk->receive_bit = receive_bit; + fsk->f0_deviation = (f0 - f1) / 2.0; + fsk->f1_deviation = (f1 - f0) / 2.0; + if (f0 < f1) { + fsk->low_bit = 0; + fsk->high_bit = 1; + } else { + fsk->low_bit = 1; + fsk->high_bit = 0; + } + + /* calculate bandwidth */ + bandwidth = fabs(f0 - f1) * 2.0; + + /* init fm demodulator */ + rc = fm_demod_init(&fsk->demod, (double)samplerate, (f0 + f1) / 2.0, bandwidth); + if (rc < 0) + goto error; + + fsk->bits_per_sample = (double)bitrate / (double)samplerate; + PDEBUG(DDSP, DEBUG_DEBUG, "Bitduration of %.4f bits per sample @ %d.\n", fsk->bits_per_sample, samplerate); + + return 0; + +error: + fsk_demod_cleanup(fsk); + return rc; +} + +/* Cleanup transceiver instance. */ +void fsk_demod_cleanup(fsk_demod_t *fsk) +{ + PDEBUG(DDSP, DEBUG_DEBUG, "Cleanup FSK for Receiver.\n"); fm_demod_exit(&fsk->demod); } @@ -150,7 +267,7 @@ void fsk_cleanup(fsk_t *fsk) * Therefore we change the sample counter only slightly, so bit slips may not * happen so quickly. */ -void fsk_receive(fsk_t *fsk, sample_t *sample, int length) +void fsk_demod_receive(fsk_demod_t *fsk, sample_t *sample, int length) { sample_t I[length], Q[length], frequency[length], f; int i; @@ -211,78 +328,3 @@ void fsk_receive(fsk_t *fsk, sample_t *sample, int length) } } -/* modulate bits - * - * If first/next bit is required, callback function send_bit() is called. - * If there is no (more) data to be transmitted, the callback functions shall - * return -1. In this case, this function stops and returns the number of - * samples that have been rendered so far, if any. - * - * For coherent mode (FSK), we round the phase on every bit change to the - * next zero crossing. This prevents phase shifts due to rounding errors. - */ -int fsk_send(fsk_t *fsk, sample_t *sample, int length, int add) -{ - int count = 0; - double phase, phaseshift; - - phase = fsk->tx_phase65536; - - /* get next bit */ - if (fsk->tx_bit < 0) { -next_bit: - fsk->tx_bit = fsk->send_bit(fsk->inst); -#ifdef DEBUG_MODULATOR - printf("bit change to %d\n", fsk->tx_bit); -#endif - if (fsk->tx_bit < 0) - goto done; - /* correct phase when changing bit */ - if (fsk->coherent) { - /* round phase to nearest zero crossing */ - if (phase > 16384.0 && phase < 49152.0) - phase = 32768.0; - else - phase = 0; - /* set phase according to current position in bit */ - phase += fsk->tx_bitpos * fsk->cycles_per_bit65536[fsk->tx_bit & 1]; -#ifdef DEBUG_MODULATOR - printf("phase %.3f bitpos=%.6f\n", phase, fsk->tx_bitpos); -#endif - } - } - - /* modulate bit */ - phaseshift = fsk->phaseshift65536[fsk->tx_bit & 1]; - while (count < length && fsk->tx_bitpos < 1.0) { - if (add) - sample[count++] += fsk->sin_tab[(uint16_t)phase]; - else - sample[count++] = fsk->sin_tab[(uint16_t)phase]; -#ifdef DEBUG_MODULATOR - printf("|%s|\n", debug_amplitude(fsk->sin_tab[(uint16_t)phase] / fsk->level)); -#endif - phase += phaseshift; - if (phase >= 65536.0) - phase -= 65536.0; - fsk->tx_bitpos += fsk->bits_per_sample; - } - if (fsk->tx_bitpos >= 1.0) { - fsk->tx_bitpos -= 1.0; - goto next_bit; - } - -done: - fsk->tx_phase65536 = phase; - - return count; -} - -/* reset transmitter state, so we get a clean start */ -void fsk_tx_reset(fsk_t *fsk) -{ - fsk->tx_phase65536 = 0; - fsk->tx_bitpos = 0; - fsk->tx_bit = -1; -} - diff --git a/src/libfsk/fsk.h b/src/libfsk/fsk.h index a7cc428..395e915 100644 --- a/src/libfsk/fsk.h +++ b/src/libfsk/fsk.h @@ -1,14 +1,12 @@ #include "../libfm/fm.h" -typedef struct ffsk { +typedef struct fsk_mod { void *inst; int (*send_bit)(void *inst); - void (*receive_bit)(void *inst, int bit, double quality, double level); - fm_demod_t demod; double bits_per_sample; /* fraction of a bit per sample */ double *sin_tab; /* sine table with correct peak level */ double phaseshift65536[2]; /* how much the phase of fsk synbol changes per sample */ - double cycles_per_bit65536[2]; /* cacles of one bit */ + double cycles_per_bit65536[2]; /* cycles of one bit */ double tx_phase65536; /* current transmit phase */ double level; /* level (amplitude) of signal */ int coherent; /* set, if coherent TX mode */ @@ -16,15 +14,27 @@ typedef struct ffsk { double f1_deviation; int low_bit, high_bit; /* a low or high deviation means which bit? */ int tx_bit; /* current transmitting bit (-1 if not set) */ - int rx_bit; /* current receiving bit (-1 if not yet measured) */ double tx_bitpos; /* current transmit position in bit */ +} fsk_mod_t; + +typedef struct fsk_demod { + void *inst; + void (*receive_bit)(void *inst, int bit, double quality, double level); + fm_demod_t demod; + double bits_per_sample; /* fraction of a bit per sample */ + double f0_deviation; /* deviation of frequencies, relative to center */ + double f1_deviation; + int low_bit, high_bit; /* a low or high deviation means which bit? */ + int rx_bit; /* current receiving bit (-1 if not yet measured) */ double rx_bitpos; /* current receive position in bit (sampleclock) */ double rx_bitadjust; /* how much does a bit change cause the sample clock to be adjusted in phase */ -} fsk_t; +} fsk_demod_t; -int fsk_init(fsk_t *fsk, void *inst, int (*send_bit)(void *inst), void (*receive_bit)(void *inst, int bit, double quality, double level), int samplerate, double bitrate, double f0, double f1, double level, int coherent, double bitadjust); -void fsk_cleanup(fsk_t *fsk); -void fsk_receive(fsk_t *fsk, sample_t *sample, int length); -int fsk_send(fsk_t *fsk, sample_t *sample, int length, int add); -void fsk_tx_reset(fsk_t *fsk); +int fsk_mod_init(fsk_mod_t *fsk, void *inst, int (*send_bit)(void *inst), int samplerate, double bitrate, double f0, double f1, double level, int coherent); +void fsk_mod_cleanup(fsk_mod_t *fsk); +int fsk_mod_send(fsk_mod_t *fsk, sample_t *sample, int length, int add); +void fsk_mod_tx_reset(fsk_mod_t *fsk); +int fsk_demod_init(fsk_demod_t *fsk, void *inst, void (*receive_bit)(void *inst, int bit, double quality, double level), int samplerate, double bitrate, double f0, double f1, double bitadjust); +void fsk_demod_cleanup(fsk_demod_t *fsk); +void fsk_demod_receive(fsk_demod_t *fsk, sample_t *sample, int length); -- cgit v1.2.3