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#define BITS_PER_SUPERFRAME 12672.0 /* super frame (Oberrahmen) has duration of exactly 2.4 seconds */
#define BITS_PER_BLOCK 198.0 /* block has duration of exactly 37.5 milli seconds */
#define BITS_PER_SPK_BLOCK 66.0 /* spk block has a duration of exactly 12.5 milli seconds */
/* fsk rx sync state */
enum fsk_sync {
FSK_SYNC_NONE = 0,
FSK_SYNC_POSITIVE,
FSK_SYNC_NEGATIVE,
};
enum demod_type {
FSK_DEMOD_AUTO, /* auto selection of the demod type below */
FSK_DEMOD_SLOPE, /* check for highest slope (good for sound cards) */
FSK_DEMOD_LEVEL, /* check for zero crossing (good for SDR) */
};
typedef struct fsk_fm_demod {
cnetz_t *cnetz; /* pointer back to cnetz instance */
/* clock */
double bit_time; /* current time in bits inside superframe */
double bit_time_uncorrected; /* same as above, but not corrected by sync */
/* bit detection */
enum demod_type demod_type; /* how to demodulate bits */
sample_t *bit_buffer_spl; /* samples ring buffer */
int bit_buffer_len; /* number of samples in ring buffer */
int bit_buffer_half; /* half of ring buffer */
int bit_buffer_pos; /* current position to write next sample */
double level_threshold; /* threshold for detection of next level change */
double bits_per_sample; /* duration of one sample in bits */
double next_bit; /* count time to detect bits */
int bit_count; /* counts bits, to match 4 bits at distributed signaling */
int last_change_positive; /* flags last level change direction */
enum fsk_sync sync; /* set, if we are in sync and what polarity we receive */
double sync_level; /* what was the level, when we received the sync */
double sync_time; /* when did we receive sync, relative to super frame */
double sync_stddev; /* standard deviation of level changes */
/* speech */
sample_t *speech_buffer; /* holds one chunk of 12.5ms */
int speech_size;
int speech_count;
/* bit decoder */
uint64_t rx_sync; /* sync shift register */
char rx_buffer[151]; /* 150 bits + termination */
int rx_buffer_count; /* counter when receiving bits */
/* statistics */
double change_levels[256]; /* ring buffer to store levels */
double change_when[256]; /* ring buffer to store time when level has changed */
uint8_t change_pos; /* index for next write */
/* display measurements */
dispmeasparam_t *dmp_frame_level;
dispmeasparam_t *dmp_frame_stddev;
/* debug */
FILE *debug_fp; /* file pointer for debugging output */
} fsk_fm_demod_t;
int fsk_fm_init(fsk_fm_demod_t *fsk, cnetz_t *cnetz, int samplerate, double bitrate, enum demod_type);
void fsk_fm_exit(fsk_fm_demod_t *fsk);
void fsk_fm_demod(fsk_fm_demod_t *fsk, sample_t *samples, int length);
void fsk_correct_sync(fsk_fm_demod_t *fsk, double offset);
void fsk_copy_sync(fsk_fm_demod_t *fsk_to, fsk_fm_demod_t *fsk_from);
void fsk_demod_reset(fsk_fm_demod_t *fsk);
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