/******************************************************************************

	humanoid project RC servo control program

	interrupt_1.c
		move LED light using timer0 interrupt

	Author		:	Takashi Tomiyama ( yij01260@nifty.com )
	Target		:	PIC16F876A
	Clock		:	20MHz
	Compiler	:	CSS-PCM
	
******************************************************************************/

/*
	peripheral setting

		RB0-7	---	LED
*/

//	history
// 	2003-03-28	ver.0

#include <16f876a.h>

#fuses	HS, NOWDT, NOPROTECT, PUT, BROWNOUT, NOLVP

//	constant definition -------------------------------------------------------

// how derive count setting 1ms interval of timer0
//		0xff - (interval time) / (cpu clock * 4) / (priscaler)
//	=	0xff - 1ms / (50ns * 4) / 64
//	=	0xff - 1000000ns / 200ns / 64
//	=	0xff - 5000 / 64
//	=	0xff - 0x4e					(78=0x4e)
//	=	0xb1

#define	TIMER0_CNT				0xb1
#define	LED_CONTROL_PERIOD_MS	100		// LED control period 100ms

// global variables	-----------------------------------------------------------
unsigned long	waitCountMs;
unsigned int8 	led   = 0x01;

// prototype declaration ------------------------------------------------------
void LED_Update(void);


// ============================================================================
//	interval timer (timer0 interrupt hander)
// ============================================================================
#int_timer0
void IntervalTimer(void)
{	
	set_timer0( TIMER0_CNT );	// 1ms interval

	if( 0 < waitCountMs )
		waitCountMs--;
}

// ============================================================================
//	main function
// ============================================================================
void main(void)
{
	waitCountMs = LED_CONTROL_PERIOD_MS;

	// setup interrupt timer0 -----------------------------
	setup_timer_0( RTCC_INTERNAL | RTCC_DIV_64 );
	set_timer0( TIMER0_CNT );	// 1ms interval

	// enable interrupt
	enable_interrupts( INT_TIMER0 );
	enable_interrupts( GLOBAL );	

	// endless loop ---------------------------------------
	while( 1 ){
		if( 0 == waitCountMs ){
			waitCountMs = LED_CONTROL_PERIOD_MS;
			LED_Update();
		}
	}
}

// ----------------------------------------------------------------------------
//	LED related function
// ----------------------------------------------------------------------------
void LED_Update(void)
{
	if( 0x80 <= led )
		led = 0x01;
	else
		led = led << 1;
		
	output_b(led);
}