Микроконтроллеры

uint8_t FSKdemod(int16_t FilterSample) {
    //#define FreqTop 37 //Freqency counter high saturation value
    //#define FreqBot 27 //Freqency counter low saturation value
#define FreqHi 34 //High freqency (space) detection threshold
#define FreqLo 30 //Low freqency (mark) detection threshold

    static struct {
        unsigned PrevSamp : 1; //Previous sample value, 1 means negative
        unsigned NewBit : 1; //Next transition bit
        unsigned Out : 1; //Output state
    } FSKstate = {0};
    static int Frequency = 32; //Start from nominal center frequency
    static uint16_t SlideBuff[4] = {0b1010101010101010}; //Sliding average 64
    //bit buffer. Center frequency (32 transitions) initially.
    static uint8_t Iteration = 0; //Iteration counter for absolute freq. update
    static uint8_t TransCnt = 0; //Bit counter for absolute frequency update
    //Check for the transition and update NewBit value as a result
    if (FilterSample & (1 << 15)) { //Check current sample sign
        if (FSKstate.PrevSamp) { //When sample is negative as previous
            FSKstate.NewBit = 0; //None transition detected
        } else {
            FSKstate.NewBit = 1; //The transition detected
        }
        FSKstate.PrevSamp = 1; //Update for next sample comparison
    } else {
        if (FSKstate.PrevSamp) { //When sample is positive but previous negative
            FSKstate.NewBit = 1; //The transition detected
        } else {
            FSKstate.NewBit = 0; //None transition detected
        }
        FSKstate.PrevSamp = 0; //Update for next sample comparison
    }
    //Update frequency value, slide buffer and redundant slide buffer bit counter
    //Update instant frequency and transition counter by new value
    if (FSKstate.NewBit) {
        TransCnt++; //Account transitions for absolute frequency value
    }
    //Update instant frequency
    //Check slide buffer transition bit to remove against new arriving bit
    if (!(SlideBuff[3]&(1 << 15))&&(FSKstate.NewBit)) {
        Frequency++; //Increase frequency if steady bit removed but transition
        //arrived
    }
    if ((SlideBuff[3]&(1 << 15))&&(!FSKstate.NewBit)) {
        Frequency--; //Decrease frequency value if a transition removed
        //but not arrived
    }
    //Update slide buffer. Shift left with carry
    if (SlideBuff[2]&(1 << 15)) { //Check for third to fourth word carry
        SlideBuff[3] = (SlideBuff[3] << 1) | 1; //Carry 3rd word MSB to 4th LSB
    } else {
        SlideBuff[3] = (SlideBuff[3] << 1); //None carry needed. Just shift
    }
    if (SlideBuff[1]&(1 << 15)) { //Check for second to third word carry
        SlideBuff[2] = (SlideBuff[2] << 1) | 1; //Carry 2nd word MSB to 3rd LSB
    } else {
        SlideBuff[2] = (SlideBuff[2] << 1); //None carry needed. Just shift
    }
    if (SlideBuff[0]&(1 << 15)) { //Check for first to second word carry
        SlideBuff[1] = (SlideBuff[1] << 1) | 1; //Carry 1th word MSB to 2nd LSB
    } else {
        SlideBuff[1] = (SlideBuff[1] << 1); //None carry needed. Just shift
    }
    if (FSKstate.NewBit) {
        SlideBuff[0] = (SlideBuff[0] << 1) | 1; //Put new value into first LSB
    } else {
        SlideBuff[0] = (SlideBuff[0] << 1); //Nothing to insert. Just shift
    }
    //Update frequency value by robust transition counter result to avoid
    //frequency error accumulation
    if (!(Iteration++&0b111111)) { //Update once per 64 iterations
        Frequency = TransCnt; //Slide buffer transitions number is frequency
        TransCnt = 0; //Clear counter for new count
    }
    if (FSKstate.Out) { //Apply thresholds depending on the last state
        if (Frequency <= FreqLo) { //Check for low threshold
            FSKstate.Out = 0;
        }
    } else {
        if (Frequency >= FreqHi) { //Check for high threshold
            FSKstate.Out = 1;
        }
    }
    return (FSKstate.Out);
    //return (Frequency | (FSKstate.Out << 14));
}

Полный код проекта, с фильтрами, декодером и выводом результата на печать, прилагаю. 9 лет лежал без движения. Но это только декодер.

FSK_serial_20_CRC_print.zip