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C-Netz: Simplifying TX signal clock sync between two channels

This commit is contained in:
Andreas Eversberg 2016-11-30 18:09:38 +01:00
parent 0b43b63d1f
commit e34d74aa23
3 changed files with 30 additions and 37 deletions
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13
src/cnetz/cnetz.c
View File

@ -84,6 +84,19 @@
* work with that.
*/
/*
* Notes on sync:
*
* The encoder generates a precise clocked signal using correction value given
* by command line. For multichannel, the second sound card's channel (slave) is
* synced to the first one (master), if calculation of signal phase might drift
* due to routing errors.
*
* The decoder is synced to the phone, whenever it receives a valid frame.
*
* See dsp.c and fsk_fm_demod.c for code about syncing.
*/
#define CHAN cnetz->sender.kanal
#include <stdio.h>

4
src/cnetz/cnetz.h
View File

@ -96,12 +96,14 @@ typedef struct cnetz {
int fsk_tx_buffer_pos; /* current position sending buffer */
double fsk_tx_bitstep; /* fraction of a bit each sample */
double fsk_tx_phase; /* current bit position */
uint64_t fsk_tx_scount; /* sample counter (used to sync multiple channels) */
int scrambler; /* 0 = normal speech, 1 = scrambled speech */
int16_t *dsp_speech_buffer; /* samples in one chunk */
int dsp_speech_length; /* number of samples */
int dsp_speech_pos; /* current position in buffer */
int frame_last_count; /* master's count position of last frame sync */
/* sync multiple channels on one sound card */
uint64_t frame_last_scount; /* master's sample count of last frame sync */
double frame_last_phase; /* master's bit phase of last frame sync */
/* audio offset removal */

50
src/cnetz/dsp.c
View File

@ -599,41 +599,27 @@ again:
/* start new telegramm, so we generate one */
if (pos == 0) {
/* measure actual signal speed */
/* a new hyper frame starts */
if (cnetz->sched_ts == 0 && cnetz->sched_r_m == 0) {
/* measure actual signal speed */
calc_clock_speed(cnetz, cnetz->sender.samplerate * 24 / 10, 1, 1);
/* sync TX */
/* sync TX (might not be required, if there is no error in math calculation) */
if (cnetz->sender.slave) {
/* we are master, so we store sample count and phase */
cnetz->frame_last_count = count;
cnetz->frame_last_scount = cnetz->fsk_tx_scount;
cnetz->frame_last_phase = cnetz->fsk_tx_phase;
}
if (cnetz->sender.master) {
/* we are slave, so we sync to sample count and phase */
/* we are slave, so we sync to phase */
cnetz_t *master = (cnetz_t *)cnetz->sender.master;
/* if we are still in sync with the sample count, we adjust the phase */
if (master->frame_last_count == count) {
PDEBUG(DDSP, DEBUG_DEBUG, "Sync slave to master: phase(master) = %.15f, phase(slave) = %.15f\n", master->frame_last_phase, cnetz->frame_last_phase);
cnetz->frame_last_phase = master->frame_last_phase;
}
/* only sync, if we do not hit the border of the sample chunk.
* this way we have slave and master sync at the same sample chunk. */
if (master->frame_last_count > 0 && master->frame_last_count < length - 1 && count > 0 && count < length - 1) {
/* if the sample count is one sample ahead, we go back one sample */
if (count == master->frame_last_count + 1) {
PDEBUG(DDSP, DEBUG_INFO, "Sync slave to master by going back one sample: phase(master) = %.15f, phase(slave) = %.15f\n", master->frame_last_phase, cnetz->frame_last_phase);
count--;
samples--;
cnetz->frame_last_phase = master->frame_last_phase;
}
/* if the sample count is one sample behind, we go forward one sample */
if (count == master->frame_last_count - 1) {
PDEBUG(DDSP, DEBUG_INFO, "Sync slave to master by going forth one sample: phase(master) = %.15f, phase(slave) = %.15f\n", master->frame_last_phase, cnetz->frame_last_phase);
count++;
*samples = samples[-1];
samples++;
cnetz->frame_last_phase = master->frame_last_phase;
}
/* it may happen that the sample count does not match with the master,
* because one has a phase wrap before and the other after a sample.
* then we do it next hyper frame cycle */
if (master->frame_last_scount == cnetz->fsk_tx_scount) {
PDEBUG(DDSP, DEBUG_DEBUG, "Sync phase of slave to master: master=%.15f, slave=%.15f, diff=%.15f\n", master->frame_last_phase, cnetz->fsk_tx_phase, master->frame_last_phase - cnetz->fsk_tx_phase);
cnetz->fsk_tx_phase = master->frame_last_phase;
} else {
PDEBUG(DDSP, DEBUG_DEBUG, "Not sync phase of slave to master: Sample counts during frame change are different, ignoring this time!\n");
}
}
}
@ -746,6 +732,7 @@ again:
}
cnetz->dsp_speech_length = speech_length;
cnetz->dsp_speech_pos = speech_pos;
cnetz->fsk_tx_scount += copy;
pos += copy;
count += copy;
if (pos == cnetz->fsk_tx_buffer_length) {
@ -780,15 +767,6 @@ void sender_send(sender_t *sender, int16_t *samples, int length)
exit(0);
}
#if 0
#warning check phase between slave and master process
/* check for sync to master */
if (sender->master) {
if (((cnetz_t *)(sender->master))->fsk_tx_phase != cnetz->fsk_tx_phase) {
printf("phase between master and slave differs: %.10f vs %.10f!\n", ((cnetz_t *)(sender->master))->fsk_tx_phase, cnetz->fsk_tx_phase);
}
}
#endif
}
/* unshrink audio segment from the duration of 60 bits to 12.5 ms */