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#include "v17dem.h"
#define INITIAL_BAUD_RATE 2400
#define INITIAL_CARRIER_FREQ 1800
#define SAMPLE_RATE 8000
#define SAMPLES_MAX (SAMPLES_RATE*5) /* -> 5s buffer */
#define SINC_RADIUS 10
struct v17dem_state {
float *samples;
int i_samples, n_samples;
int sample_index;
int baud_rate;
int carrier_freq;
struct interpol_state qam_interpol;
struct interpol_state am_interpol;
enum { COSINUS, SINUS } current;
float *xam, *yam;
int am_index;
};
void v17dem_init(struct v17dem_state *s) {
assert(s);
memset(s, 0, sizeof(struct v17dem_state));
s->baud_rate = INITIAL_BAUD_RATE;
s->carrier_freq = INITIAL_CARRIER_FREQ;
s->samples = malloc(sizeof(float) * SAMPLES_MAX * 2);
interpol_init(&s->qam_interpol, 9, SINC_RADIUS);
}
void v17dem_done(struct v17dem_state *s) {
assert(s);
free(s->samples);
inertpol_done(&s->qam_interpol);
}
static void move_to_front(struct v17dem_state *s) {
assert(s);
if (s->i_samples < SAMPLES_MAX)
return;
memmove(s->samples, s->samples + s->i_samples, s->n_samples*sizeof(float));
s->i_samples = 0;
}
void v17dem_push(struct v17dem_state *s, const float *p, int l){
assert(s && p && l);
assert(l <= SAMPLES_MAX-s->n_samples);
move_to_front(s);
memcpy(s->samples + s->i_samples + s->n_samples, p, l*sizeof(float));
s->n_samples += l;
}
int v17dem_pull(struct v17dem_state *s, uint8_t *p, int l){
int alt = 0;
assert(s && p && l);
for (;;) {
int n;
/* Position für AM-Abtastung im Sample-Puffer berechnen -- alle 90° */
float x = (SAMPLE_RATE/(4.0*s->carrier_freq) * s->am_index) - s->sample_index;
assert(x >= 0);
/* AM-Abtatsung druchführen */
if (s->current = COSINUS)
am = s->xam;
else
am = s->yam;
am[s->am_index] = interpol_get(s->qam_interpol, s->samples + s->i_samples, s->n_samples, x);
if (s->current == SINUS)
s->am_index++;
s->current = !s->current;
/* Überflüssige Sampledaten killen */
n = (int) (x - (float) SINC_RADIUS*SAMPLE_RATE/s->carrier_freq/4);
if (n > 0) {
s->n_samples -= n;
s->i_samples += n;
s->sample_index += n;
}
}
}
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