// main.c

#include <pic.h>

__CONFIG(INTIO & WDTDIS & MCLRDIS & BORDIS & UNPROTECT & PWRTEN);

void Update(void);

void main(void)
{
	// Load Factory Calibration Value Into OSCCAL
	#asm
	call 0x3FF
	bsf	_STATUS,5					 				
	movwf _OSCCAL						
	#endasm

	TRISIO = 0b11001111;                 // RA4,RA5 are outputs
	GPIO = 0x00;                        //Clear GPIO (all LEDs off)
	VRCON = 0x00;                       //Turn Off Voltage Reference Peripheral
	CMCON = 0x07;                        //Turn Off Comparator Peripheral
	TMR0 = 0x00;                        //Clear Timer0
	OPTION = 0b10000010;               //Set Timer0 Prescaler To Fast Flash LED's

	ANSEL = 0b01010001;			// set A/D rate TOSC/16 (4us) and set AN0 as analog input
	ADCON0 = 0b00000001;		// configure Vdd ref, MSB in ADRESH, AN0, A/D enabled

	GODONE = 1;

	T0IE = 1;                          //Timer0 Overflow Interrupt Enabled
	T0IF = 0;                        //Clear Timer0 Overflow Interrupt Flag
	GIE = 1;                           //Enable All Interrupts

	for (;;);
}

void interrupt Isr(void)
{
	if (T0IE & T0IF)  	  //If A Timer0 Interrupt, Then
	{
		Update();
		T0IF = 0;                 //Clear Timer0 Interrupt Flag
	}
	return;
}

static unsigned char	State = 2;		// 0 = red, 1 = yellow, 2 = green
										// start in green state

void ReadAD(void)
{
	unsigned char	reading;

	if (GODONE == 1)		return;		// not finished

	reading = ADRESH;

	GODONE = 1;		// read again

	// 255 = 5V -> 15V battery level
	// 8V battery level -> 136
	// 8.2V battery level -> 140
	// 8.4V battery level -> 142

	if (reading <= 136)			State = 0;
	else if (reading <= 142)	State = 1;
	else						State = 2;
}

static unsigned char	WhichLed = 0;	// LED to light next
static unsigned char	Phase = 0;

void Update(void)
{
	unsigned char	output = 0;		// no LEDs on

	ReadAD();

	switch (WhichLed)
	{
		case 0: // red
			if (State < 2)		output = 0b00010000;		// RA4 = 1, RA5 = 0
			break;
		case 1:	// green
			if (State > 0)		output = 0b00100000;		// RA5 = 1, RA4 = 0
			break;
	}

	if ((State == 0) && (Phase & 128))	output = 0;		// flash red

	GPIO = output;
	WhichLed ^= 1;
	Phase++;
}