#define F_CPU 16000000UL

// the number of cycles it does after one loop is 10
#define CYCLES  10

// 1 tick at 16mhz = 0,0000000625. 1/f_cpu.
// RESOLUTION = F_CPU / CYCLES /‭ 16777215‬ 24bit
#define RESOLUTION  0.095367431640625



volatile uint8_t runstate;      // indicate on/off
volatile uint8_t signal;        // signal type
volatile double frequency;    //frequency value
volatile uint32_t acc;


const uint8_t sinewave[] PROGMEM = { 0x80,0x83,0x86,... }
const uint8_t *SIGNALS[] = { sinewave, .... };

inline void static signalOutOLD(const uint8_t *signal, uint8_t ad2, uint8_t ad1, uint8_t ad0)
{
    asm volatile(
        "eor r18, r18   ;r18<-0"
        "eor r19, r19   ;r19<-0"
        "1:"
        "add r18, %0    ;1 cycle, (ad0) variable to r18"
        "adc r19, %1    ;1 cycle, (ad1) variable to r19"
        "adc %A3, %2    ;1 cycle, (ad2) variable to r30"
        "lpm            ;3 cycles, load byte to r0 from Z pointed"
        "out %4, r0     ;1 cycle, Output data value on r0 to PortD"
        "sbis %5, 2     ;1 cycle if PB2 is set skip the jump."
        "rjmp 1b        ;2 cycles, jump to 1: in unix style. 10 cycles tot"
        :
        :"r" (ad0),"r" (ad1),"r" (ad2),"e" (signal),"I" (_SFR_IO_ADDR(PORTD)), "I" (_SFR_IO_ADDR(PORTB))
        :"r18", "r19"
    );
}

// function is called from ISR(SPI_STC_vect) when the start|stop command is received.
void set_runstate(void) {
    // toggle the state.
    runstate = !runstate;
    BITS_FLIP(PORTB, PB2);
}

int main(void) {

    // test led light1,
    BITS_SET(DDRB, PB1);
    BITS_CLEAR(PORTB, PB1);

    // asm stop bit.  a led is connected to this port to indicate when the bit is set.
    BITS_SET(DDRB, PB2);
    BITS_SET(PORTB, PB2);

    runstate  = 0;
    signal    = 0;    // signal type
    frequency = 1000; //frequency value
    acc = frequency / RESOLUTION ;


    while(1)
    {
        while(runstate == 1)
        {
            signalOutOLD(SIGNALS[signal], (uint8_t)(acc >> 16), (uint8_t)(acc >> 8), (uint8_t)acc);
        }
        _delay_ms(100);
        BITS_FLIP(PORTB, PB1);
    }
    return 0;
}