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btstack_sample_rate_compensation: refactoring and documentation

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Dirk Helbig 2023-01-31 14:47:16 +01:00 committed by Matthias Ringwald
parent 555ade44f7
commit 0d212321a9
2 changed files with 45 additions and 11 deletions
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20
src/btstack_sample_rate_compensation.c
View File

@ -37,17 +37,17 @@
#define BTSTACK_FILE__ "btstack_sample_rate_comnpensation.h"
#include <stdio.h>
#include "btstack.h"
#include "btstack_sample_rate_compensation.h"
void btstack_sample_rate_compensation_reset( btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms ) {
void btstack_sample_rate_compensation_reset(btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms) {
self->count = 0;
self->last = timestamp_ms;
}
void btstack_sample_rate_compensation_init( btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms, uint32_t sample_rate, uint32_t ratioQ15 ) {
void btstack_sample_rate_compensation_init(btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms, uint32_t sample_rate, uint32_t ratio_Q15) {
btstack_sample_rate_compensation_reset( self, timestamp_ms );
self->ratio_state = ratioQ15 << 1; // Q15 to Q16 is one left shift
self->ratio_state = ratio_Q15 << 1; // Q15 to Q16 is one left shift
self->rate_state = sample_rate << 8;
#ifdef DEBUG_RATIO_CALCULATION
self->ratio = Q15_TO_FLOAT(ratioQ15);
@ -55,10 +55,10 @@ void btstack_sample_rate_compensation_init( btstack_sample_rate_compensation_t *
#endif
}
uint32_t btstack_sample_rate_compensation_update( btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms, uint32_t samples, uint32_t playback_sample_rate ) {
uint32_t btstack_sample_rate_compensation_update(btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms, uint32_t samples, uint32_t playback_sample_rate) {
int32_t delta = timestamp_ms - self->last;
if( delta >= 1000 ) {
printf("current playback sample rate: %d\n", playback_sample_rate );
log_debug("current playback sample rate: %d", playback_sample_rate );
#ifdef DEBUG_RATIO_CALCULATION
{
@ -80,7 +80,7 @@ uint32_t btstack_sample_rate_compensation_update( btstack_sample_rate_compensati
#endif
uint32_t fixed_rate = (self->count*(UINT16_C(1)<<15))/delta*1000; // sample rate as Q15
uint32_t fixed_ratio = (self->rate_state<<7)/playback_sample_rate; // Q15
printf("fp current l2cap sample rate: %f (%d %d)\n", Q15_TO_FLOAT(fixed_rate), delta, self->count);
log_debug("fp current l2cap sample rate: %f (%d %d)", Q15_TO_FLOAT(fixed_rate), delta, self->count);
self->last = timestamp_ms;
self->count = 0;
@ -94,9 +94,9 @@ uint32_t btstack_sample_rate_compensation_update( btstack_sample_rate_compensati
const int16_t ratio_decay = FLOAT_TO_Q8(1.3f);
self->ratio_state += (ratio_decay * (int32_t)((fixed_ratio<<1)-self->ratio_state)) >> (16-8); // Q16
printf("fp current ratio : %f\n", Q15_TO_FLOAT(fixed_ratio));
printf("fp calculated ratio: %f\n", Q16_TO_FLOAT(self->ratio_state));
printf("scale factor Q16: %d\n", self->ratio_state);
log_debug("fp current ratio : %f", Q15_TO_FLOAT(fixed_ratio));
log_debug("fp calculated ratio: %f", Q16_TO_FLOAT(self->ratio_state));
log_debug("scale factor Q16: %d", self->ratio_state);
}
self->count += samples;

36
src/btstack_sample_rate_compensation.h
View File

@ -35,6 +35,17 @@
*
*/
/**
* @title Sample rate compensation
*
* Prevents buffer over/under-run at the audio receiver by compensating for varying/different playback/receiving sample rates.
*
* Intended to measure the L2CAP packet sample rate and with the provided playback sample rate calculates a compensation ratio
* which compensates for drift between playback and reception.
*
* Requires the audio interface to provide the current playback sample rate.
*
*/
#ifndef BTSTACK_SAMPLE_RATE_COMPENSATION_H_
#define BTSTACK_SAMPLE_RATE_COMPENSATION_H_
@ -45,6 +56,8 @@
extern "C" {
#endif
/* API_START */
#define FLOAT_TO_Q15(a) ((signed)((a)*(UINT16_C(1)<<15)+0.5f))
#define FLOAT_TO_Q8(a) ((signed)((a)*(UINT16_C(1)<<8)+0.5f))
#define FLOAT_TO_Q7(a) ((signed)((a)*(UINT16_C(1)<<7)+0.5f))
@ -68,10 +81,31 @@ typedef struct {
#endif
} btstack_sample_rate_compensation_t;
void btstack_sample_rate_compensation_reset( btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms );
/**
* @brief Initialize sample rate compensation
* @param self pointer to current instance
* @param time stamp at which to start sample rate measurement
*/
void btstack_sample_rate_compensation_init( btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms, uint32_t sample_rate, uint32_t ratioQ15 );
/**
* @brief reset sample rate compensation
* @param self pointer to current instance
* @param time stamp at which to start sample rate measurement
*/
void btstack_sample_rate_compensation_reset( btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms );
/**
* @brief update sample rate compensation with the current playback sample rate decoded samples
* @param self pointer to current instance
* @param time stamp for current samples
* @param samples for current time stamp
* @param playback sample rate
*/
uint32_t btstack_sample_rate_compensation_update( btstack_sample_rate_compensation_t *self, uint32_t timestamp_ms, uint32_t samples, uint32_t playback_sample_rate );
/* API_END */
#if defined __cplusplus
}
#endif