AVR-Chat

>    Date: Sun, 19 Mar 2006 13:52:28 +1100
>    From: "OWEN-A" <oldboot@bigpond.com>
> Subject: Long delays
> 
> I need to generate delays of up to 24 hours on a Mega16 has anyone
> any suggestions, I could use an RTC but there may be another option
as
> strict timekeeping is not necessary for this application.
> Thanking You,
> 
> Owen.

Hi Owen,

Use the timer1 - see the actual code below I wrote.

Robert J Rademacher

//TIMER1 initialisation - prescale:256
// WGM: 0) Normal, TOP=0xFFFF
// desired value: 1Sec
// actual value:  1.000Sec (0.0%)
// Crystal: 14.7456Mhz
void timer1_init(void)
{
 TCCR1B = 0x00; //stop
 TCNT1H = 0x1F; //setup
 TCNT1L = 0x01;
 OCR1AH = 0xE0;
 OCR1AL = 0xFF;
 OCR1BH = 0xE0;
 OCR1BL = 0xFF;
 ICR1H  = 0xE0;
 ICR1L  = 0xFF;
 TCCR1A = 0x00;
 TCCR1B = 0x04; //start Timer
}

#pragma interrupt_handler timer1_ovf_isr:9
void timer1_ovf_isr(void)
{
 //TIMER1 has overflowed
 TCNT1H = 0x1F; //reload counter high value
 TCNT1L = 0x01; //reload counter low value

//global - unsigned int OneSecCounter;
//global - unsigned int OneHourCounter;
//OneSecCounter can reaches 65535 as the max  
//total seconds, which would be 18.2041 hour, which is
//not practical when counting hours.
//Best method would be relying on 1 hour counter based
//on counting the seconds to reach 3600 secs. 
//Example.
//One hour = 60 secs x 60 mins (3600 secs)
//Make sure you reset OneSecCounter & OneHourCounter
//when starting the OneSecCounter/OneHourCounter timers.
//This OneHourCounter can reach 65,5535 hours, which is
//more than sufficient.

 OneSecCounter++;
 if (OneSecCounter >= 3600) {
     OneHourCounter++;
     OneSecCounter = 0;//reset
 }
 
}


//call this routine to initialise all peripherals
void init_devices(void)
{
 //stop errant interrupts until set up
 CLI(); //disable all interrupts
 port_init();
 timer1_init();

 MCUCR = 0x00;
 GICR  = 0x00;
 TIMSK = 0x04; //timer interrupt sources
 SEI(); //re-enable interrupts
 //all peripherals are now initialised
}

//
void main(void)
{
 init_devices();
 OneSecCounter = 0;
 OneHourCounter = 0;

 for (;;) {

     if (OneHourCounter == 1) printf("One Hour Timer Elasped!\n");
     if (OneHourCounter == 12) printf("Twelve Hours Timer Elasped!\n");
     if (OneHourCounter == 24) printf("Twenty-Four Hour Timer
Elasped!\n");

 }

}



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