systimer.c

AVR mp3 embedded program code support IDE with FAT16

//*****************************************************************
//
// File Name	: 'systimer.c'
// Title			: Procyon MP3 player system timer code
// Author		: Pascal Stang
// Date			: 11/22/2000
// Version		: 0.1
// Target MCU	: ATmega103
// Editor Tabs	: 3
//
//*****************************************************************

#include <io.h>
#include <signal.h>
#include <interrupt.h>

#include "global.h"

#include "systimer.h"

// Clock prescaling
// 0 = STOP
// 1 = CLOCK			tics= 4MHz			overflow= 15625Hz
// 2 = CLOCK/8			tics= 500kHz		overflow= 1953.125Hz
// 3 = CLOCK/64		tics= 62500Hz		overflow=  244.141Hz
// 4 = CLOCK/256		tics= 15625Hz		overflow=   61.035Hz
// 5 = CLOCK/1024		tics= 3906.25Hz	overflow=   15.259Hz
#define TIMER0CLOCK		0x04	// timer 0 prescaler

volatile unsigned int TimeReg0;
volatile unsigned int TimeReg1;

SIGNAL(SIG_OVERFLOW0)		// interrupt handler for tcnt0 overflow interrupt
{
	TimeReg0++;					// increment low byte counter

	if(!TimeReg0)				// if low byte counter rollover
	{
		TimeReg1++;				// increment high byte counter	
	}
}

void timerPause(unsigned int pausetime)
{
	register unsigned int endtime = TimeReg0+(pausetime>>5);
	while(TimeReg0 != endtime);
}

void timerInit0(void)
{

	outp((1<<TOIE0), TIMSK);	// enable TCNT0 overflow
	outp(TIMER0CLOCK, TCCR0);	// count with cpu clock/1024
	outp(0, TCNT0);				// reset TCNT0

	TimeReg0 = 0;					// initialize time registers
	TimeReg1 = 0;					// initialize time registers

	sei();							// enable interrupts
}

// delay for a minimum of <us> microseconds 
// the time resolution is dependent on the time the loop takes 
// e.g. with 4Mhz and 5 cycles per loop, the resolution is 1.25 us 

void delay(unsigned short us) 
{
	unsigned short delay_loops;
	register unsigned short i;

	delay_loops = (us+3)/5*CYCLES_PER_US; // +3 for rounding up (dirty) 

	// one loop takes 5 cpu cycles 
	for (i=0; i < delay_loops; i++) {};
}