Subversion Repositories FlightCtrl

/***********************************************************************************************************************************
* File:                 timer.c
*
* Purpose:              sets up a flag that is coming up every 2 ms
*
* Functions:    void init_Timer0(void)
*                               ISR(TIMER0_COMP_vect)
*                               unsigned char Flag2ms()
*
* hardware:             AVR-Ctrl experimental board without LCD display as I2C bus is used
*
* Created:              Jan 2013
*
* Version:              1.00    experimental version
*
* Copyright:    (c)2013 dk9nw -at- darc.de
*                               All rights reserved. This software is available only for non-commercial amateur radio or educational applications.  
*                               Other uses are prohibited. This software may be modified only if
*                               the resulting code be made available publicly and the original author(s) given credit.
*
***********************************************************************************************************************************/
#include "timer.h"

#include <stdlib.h>
#include <stdio.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
#include <avr/interrupt.h>


volatile unsigned char c2ms = 0;                // flag that switches on every 2 milliseconds



// *************************************************************************************************************
// Purpose:             Function to init Timer0
// Input:               none
// Returns:     none
// --------------------------------------
void init_Timer0(void)
{
        // TCCR0 = Timer/Counter Control Register -> FOC0 WGM00 COM01 COM00 WGM01 CS02 CS01 CS00
        // -------------------------------------------------------------------------------------
        // WGM = Waveform Generation Mode = 10 = Clear Timer on Compare Match (CTC) mode
        TCCR0 |= (1<<WGM01);    // CTC Compare Mode
        TCCR0 &= ~(1<<WGM00);   // CTC Compare Mode
       
        // TCCR0 = Timer/Counter Control Register -> FOC0 WGM00 COM01 COM00 WGM01 CS02 CS01 CS00
        // -------------------------------------------------------------------------------------
        // CS02 CS01 CS00 The three Clock Select bits select the clock source to be used by the Timer/Counter
        TCCR0 |= (1<<CS02);                             // prescale = 100 = clkI/O/256 (From prescaler)
        TCCR0 &= ~((1<<CS01)|(1<<CS00));        // prescale = 100 = clkI/O/256 (From prescaler)

        OCR0 = 126;                                                     // 1/(Fcpu/256) * 126 = 2.016 ms

        // TIMSK = Timer/Counter Interrupt Mask Register -> OCIE2 TOIE2 TICIE1 OCIE1A OCIE1B TOIE1 OCIE0 TOIE0
        // OCIE0 = Timer/Counter0 Output Compare Match Interrupt Enable
        //
        TIMSK |= (1<<OCIE0);                            // Interrupt Enabled

        c2ms = 0;
}
// *** EOF: void init_Timer0(void) ****************************************************************************




// ***************************************************
// Purpose:             ISR is called at TIMER0 Compare match
//
ISR(TIMER0_COMP_vect)
{
        c2ms = 1;              
}
// *** EOF: ISR **************************************




// **********************************************************************************************
// Function returns 0 as long as the 2 msec Interrupt Flag of Timer0 is not set and resets it
// Input:               none
// Returns:     ck
//
unsigned char Flag2ms(void)
{
        static unsigned char ck = 0;

        ck = c2ms;
        c2ms = 0;  
        return ck;
}
// *** EOF: Flag2ms() ****************************************************************************




// ********************************** EOF: timer.c **************************************************************************