armod/preamble.c

#include <stdint.h>
#include <string.h>

// debug
#ifdef __XC16
#include <xc.h>
#endif 

#ifdef __XC16
#include <libq.h>
#include <dsp.h>
#endif 

#include "../ringbuf.h"
#include "modem_types.h"

#include "preamble.h"

#include "../peripheral/gpio.h" //debug
#include "../mini-printf.h" 


#if defined(__DEBUG) && ! defined(__MPLAB_DEBUGGER_PK3)
#include "../peripheral/uarts.h"
extern fractional debug_value3;
#endif

// preambolo
uint8_t modem_preamble_waiting, modem_post_preamble_delay, modem_post_preamble_timer;
// uint8_t modem_preamble_pending, modem_preamble_done;
uint16_t BuffersPerPreamble;

fractional sync_values_sequence[(MODEM_PREAMBLE_LENGTH * MAX_BUFFERS_PER_SYMBOL)];
_Q15_16 preamble_squelch_distance;

void modem_set_up_preamble(void) {
    uint8_t sync_symbols[MODEM_PREAMBLE_LENGTH];
    modem_generate_preamble(sync_symbols);
    modem_generate_preamble_fingerprint(sync_symbols, sync_values_sequence, mod.buffers_per_symbol);
    BuffersPerPreamble = MODEM_PREAMBLE_LENGTH * mod.buffers_per_symbol;

    preamble_squelch_distance = _Q16mpy(modem_get_preamble_max_correlation_index(sync_symbols), _Q16ftoi(MODEM_PREAMBLE_SQUELCH));

    modem_post_preamble_delay = BUFFER_RATE / mod.symbol_rate; // un simbolo
}

uint8_t modem_generate_preamble(uint8_t *ModulationSymbolsBuffer) {
    uint8_t i;
    // barker code con N=13
    uint8_t sync_sequence[13] = {1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1};

    for (i = 0; i < MODEM_PREAMBLE_LENGTH; i++) {
        if (sync_sequence[i]) {
            ModulationSymbolsBuffer[i] = (mod.alphabet_size - 1);
        } else {
            ModulationSymbolsBuffer[i] = 0;
        }
    }
    return MODEM_PREAMBLE_LENGTH;
}

// trasforma la sequenza di simboli nella sua rappresentazione in sottosimboli

void modem_generate_preamble_fingerprint(uint8_t *ModulationSymbolsBuffer, fractional *symbols_values_sequence, uint8_t values_per_symbol) {
    uint8_t i, l, m = 0;
    for (i = 0; i < MODEM_PREAMBLE_LENGTH; i++) {
        for (l = 0; l < values_per_symbol; l++) {
            symbols_values_sequence[m] = detector_constellation[ModulationSymbolsBuffer[i]].frequency;
            m++;
        }
    }
}

// trova indice di correlazione massimo per la data modulationz

_Q15_16 modem_get_preamble_max_correlation_index(uint8_t *ModulationSymbolsBuffer) {
    uint8_t i;
    _Q15_16 symbol_mass = 0;
    _Q15_16 mass = 0;
    for (i = 0; i < MODEM_PREAMBLE_LENGTH; i++) {
        symbol_mass = __builtin_mulss(
                detector_constellation[ModulationSymbolsBuffer[i]].frequency,
                detector_constellation[ModulationSymbolsBuffer[i]].frequency);
        mass += symbol_mass;
    }
    return mass * mod.buffers_per_symbol;
}
/// riconosce preambolo

uint8_t modem_detect_preamble(fractional insymbol) {
    static _Q15_16 somigl_hist;
    static fractional in_sym_ringbuf[MODEM_PREAMBLE_SEARCH_BUFF_SIZE];
    static uint16_t in_sym_ringbuf_index;

    uint8_t found = 0;
    uint16_t i;
    _Q15_16 distance_accu = 0;

    // mette nel ringbuffer
    in_sym_ringbuf[in_sym_ringbuf_index] = insymbol;

    // correla
    for (i = 0; i < BuffersPerPreamble; i++) {
        // product

        distance_accu += __builtin_mulss(
                in_sym_ringbuf[ringbuf_idx_from_end(&in_sym_ringbuf_index, MODEM_PREAMBLE_SEARCH_BUFF_SIZE_MASK, (BuffersPerPreamble - i))],
                sync_values_sequence[i]);
    }


#if defined(__DEBUG) && ! defined(__MPLAB_DEBUGGER_PK3)
    debug_value3 = _Q16shr(distance_accu, 16);
#endif
/*
    if (distance_accu > preamble_squelch_distance) LATBbits.LATB3 = 1;
    else {
        LATBbits.LATB3 = 0;
    }
  */  
    if ((distance_accu > preamble_squelch_distance) && (somigl_hist > distance_accu)) {
        // trovato !
        
         //resetta il riconoscimento di preambolo
        somigl_hist = 0;
        memset(in_sym_ringbuf, 0, MODEM_PREAMBLE_SEARCH_BUFF_SIZE * sizeof (in_sym_ringbuf));
        in_sym_ringbuf_index = 0;

        found = 1;
    } else {
        somigl_hist = distance_accu;
        ringbuf_increment(&in_sym_ringbuf_index, MODEM_PREAMBLE_SEARCH_BUFF_SIZE_MASK);
    }
    return found;
}