m17.c

//--------------------------------------------------------------------
// M17 C library - m17.c
//
// Wojciech Kaczmarski, SP5WWP
// M17 Project, 5 January 2024
//--------------------------------------------------------------------
#include <m17.h>

/**
 * @brief Generate symbol stream for a preamble.
 * 
 * @param out Frame buffer (192 floats)
 * @param cnt Pointer to a variable holding the number of written symbols.
 * @param type Preamble type (pre-BERT or pre-LSF).
 */
void send_preamble(float out[SYM_PER_FRA], uint32_t *cnt, const uint8_t type)
{
    if(type) //pre-BERT
    {
        for(uint16_t i=0; i<SYM_PER_FRA/2; i++) //40ms * 4800 = 192
        {
            out[(*cnt)++]=-3.0;
            out[(*cnt)++]=+3.0;
        }
    }
    else //pre-LSF
    {
        for(uint16_t i=0; i<SYM_PER_FRA/2; i++) //40ms * 4800 = 192
        {
            out[(*cnt)++]=+3.0;
            out[(*cnt)++]=-3.0;
        }
    }
}

/**
 * @brief Generate symbol stream for a syncword.
 * 
 * @param out Output buffer (8 floats).
 * @param cnt Pointer to a variable holding the number of written symbols.
 * @param syncword Syncword.
 */
void send_syncword(float out[SYM_PER_SWD], uint32_t *cnt, const uint16_t syncword)
{
    for(uint8_t i=0; i<SYM_PER_SWD*2; i+=2)
    {
        out[(*cnt)++]=symbol_map[(syncword>>(14-i))&3];
    }
}

//send the data (can be used for both LSF and frames)
/**
 * @brief Generate symbol stream for frame contents (without syncword).
 * Can be used for both LSF and data frames.
 * 
 * @param out Output buffer (184 floats).
 * @param cnt Pointer to a variable holding the number of written symbols.
 * @param in Data input.
 */
void send_data(float out[SYM_PER_PLD], uint32_t *cnt, const uint8_t* in)
{
	for(uint16_t i=0; i<SYM_PER_PLD; i++) //40ms * 4800 - 8 (syncword)
	{
        out[(*cnt)++]=symbol_map[in[2*i]*2+in[2*i+1]];
	}
}

/**
 * @brief Generate symbol stream for the End of Transmission marker.
 * 
 * @param out Output buffer (192 floats).
 * @param cnt Pointer to a variable holding the number of written symbols.
 */
void send_eot(float out[SYM_PER_FRA], uint32_t *cnt)
{
    for(uint16_t i=0; i<SYM_PER_FRA; i++) //40ms * 4800 = 192
    {
        out[(*cnt)++]=eot_symbols[i%8];
    }
}