ATtiny45 I2C Summensignal

/*
 * main.c
 *
 *  Created on: 18.06.2011
 *      Author: peka
 */

//#define F_CPU = 20MHz //(ext Crystal)

// Defines
#define setBit(ADDRESS, BIT)    (ADDRESS |=  (1<<BIT))
#define clrBit(ADDRESS, BIT)    (ADDRESS &=  ~(1<<BIT))
#define tglBit(ADDRESS, BIT)    (ADDRESS ^=  (1<<BIT))
#define getBit(ADDRESS, BIT)    ((ADDRESS & (1<<BIT))?1:0)
#define lowByte(WORD)           ((uint8_t)(WORD))
#define highByte(WORD)          ((uint8_t)(((uint16_t)(WORD)) >> 8))
#define getWord(HIGH,LOW)       (((uint16_t)HIGH << 8) | LOW)

#define TWI_ADDR                20 <<1    // --> Address 20
// Includes
#include <avr/io.h>
#include <avr/interrupt.h>
#include "usiTwiSlave.h" //I2C Lib
// Global Vars
volatile uint16_t timerCounter = 0;
volatile uint16_t pulseTimer = 0;
volatile uint8_t servoIndex = 0;
volatile uint16_t servoPos0 = 0;
volatile uint16_t servoPos1 = 0;
volatile uint16_t servoPos2 = 0;
volatile uint16_t servoPos3 = 0;
volatile uint16_t servoPos4 = 0;
volatile uint16_t servoPos5 = 0;
volatile uint16_t servoPos6 = 0;
volatile uint16_t servoPos7 = 0;
volatile uint16_t syncTime = 0;
volatile uint8_t updateFlag = 0;

// Main Program
int main(void)
{
    // Timer 1
    setBit(TCCR1, CS10); // Prescaler 16 - 800ns Auflösung
    setBit(TCCR1, CS12);
    setBit(TIMSK, OCIE1A); // Timer/Counter1, Output Compare A Match Interrupt Enable
    OCR1A = 250; // 200µs

    // RCRx Interrupt
    clrBit(DDRB, PB1); //Input
    setBit(PORTB, PB1); //int. Pullup
    setBit(GIMSK, PCIE); //Pin Change Interrupt Enable
    PCMSK = 0x00;
    setBit(PCMSK, PCINT1); //Enable PCINT only on PB1

    // TWI
    usiTwiSlaveInit(TWI_ADDR); // TWI starten
    for (int i = 0; i < 24; i++) // Buffer füllen
        txbuffer[i] = 0xFF;

    // Interrupts aktivieren
    sei();

    // Hauptprogrammschleife
    while (1)
    {
        while (updateFlag == 0)
        {
            ; //warte auf neue servoPosition
        }

        txbuffer[0] = 0; //dataReady Flag
        txbuffer[1] = highByte(servoPos0);
        txbuffer[2] = lowByte(servoPos0);
        txbuffer[3] = highByte(servoPos1);
        txbuffer[4] = lowByte(servoPos1);
        txbuffer[5] = highByte(servoPos2);
        txbuffer[6] = lowByte(servoPos2);
        txbuffer[7] = highByte(servoPos3);
        txbuffer[8] = lowByte(servoPos3);
        txbuffer[9] = highByte(servoPos4);
        txbuffer[10] = lowByte(servoPos4);
        txbuffer[11] = highByte(servoPos5);
        txbuffer[12] = lowByte(servoPos5);
        txbuffer[13] = highByte(servoPos6);
        txbuffer[14] = lowByte(servoPos6);
        txbuffer[15] = highByte(servoPos7);
        txbuffer[16] = lowByte(servoPos7);
        txbuffer[17] = highByte(syncTime);
        txbuffer[18] = lowByte(syncTime);
        txbuffer[0] = 1; //dataReady Flag

        updateFlag = 0;
    }
}

ISR( TIMER1_COMPA_vect )
{
    TCNT1 = 0;
    pulseTimer++; // 1 tick = 200µs
}

ISR( PCINT0_vect )
{

    if (getBit(PINB, PB1) == 0) //fallende Flanke
    {
        uint16_t pulseTimerFraction = 5 * TCNT1 / 4;
        uint16_t pulseTime = pulseTimer * 200 + pulseTimerFraction; // 1 tick = 1µs

        TCNT1 = 0; // timer zurücksetzen
        pulseTimer = 0;

        if (pulseTime > 3000) //Pulspause > 3000µs --> Sync
        {
            servoIndex = 0; //nächster Puls wird wieder die länge von Servo0 angeben
            syncTime = pulseTime;
            updateFlag = 1; //servowerte dürfen in der hauptschleife ins i2c buffer geschrieben werden
        }
        else // if (pulseTime > 500) //filtere mini-spikes
        {
            if (servoIndex == 0)
                servoPos0 = pulseTime;
            else if (servoIndex == 1)
                servoPos1 = pulseTime;
            else if (servoIndex == 2)
                servoPos2 = pulseTime;
            else if (servoIndex == 3)
                servoPos3 = pulseTime;
            else if (servoIndex == 4)
                servoPos4 = pulseTime;
            else if (servoIndex == 5)
                servoPos5 = pulseTime;
            else if (servoIndex == 6)
                servoPos6 = pulseTime;
            else if (servoIndex == 7)
                servoPos7 = pulseTime;

            servoIndex++; //nächster Puls wird nächsten Servowert eben oder sync sein.
        }
    }

}