Split FSK modem code into separate modulator and demodulator

2 files changed, 158 insertions, 106 deletions

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);