main.c

#include <stdlib.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
#include <avr/wdt.h>        // Supplied Watch Dog Timer Macros 
#include <util/delay.h>
#include "utilz.h"

// LED 
#define LED_PIN PB3 	
#define LED_DURATION 500
#define FULL_CHARGE_MV 4800
#define MAX_READINGS 10	// DSP

int reading_index = 0;
long total = 0;
long average = 0;
long readings[MAX_READINGS];

void disable_adc()
{
	ADCSRA &= ~(1 << ADEN);
}

long read_vcc()
{
	// Clear previous
	ADMUX &= ~0x0F;

	// Configure ADMUX register
	ADMUX |=
		(0 << ADLAR)|
		(0 << MUX0) | 
		(0 << MUX1) | 
		(1 << MUX2) |  
		(1 << MUX3) | // Use Band Gap as Vref
		(0 << REFS0)| 
		(0 << REFS1); // Set refs0 and 1 to 0 to use Vcc as Vref

	// Configure ADCSRA register
	ADCSRA |=
		(1 << ADEN)| // Set ADEN bit to 1 to enable the ADC
		(0 << ADSC); // Set ADSC to 0 to make sure no conversions are happening

	// Wait for Vref to settle
  	_delay_us(250);

	// Start conversion
	ADCSRA |= (1 << ADSC);

	// Measure
	while (((ADCSRA >> ADSC) & 1)){}

	uint8_t low  = ADCL; // must read ADCL first - it then locks ADCH  
	uint8_t high = ADCH; // unlocks both

	long result = (high << 8) | low;
	result = 1126400L / result; // Calculate Vcc (in mV); 1126400 = 1.1*1024*1000

	ADCSRA = 0; // Turn off ADC
  	return result; // Vcc in millivolts
}

void wdt_reset_safety()
{
	cli(); 
	// The MCU Status Register provides information on which reset source caused an MCU Reset.
	// Test to see if it was the Watchdog timer - if it was disable it to avoid an infinite reset 
	// loop.
	if (MCUSR & (1 << WDRF))
	{            
		// If a reset was caused by the Watchdog Timer...
		MCUSR &= ~(1 << WDRF);                  // Clear the WDT reset flag
		WDTCR |= ((1 << WDCE) | (1 << WDE));    // Enable the WD Change Bit
		WDTCR  = 0x00;                      	// Disable the WDT
	}
	sei();
}

void init_wdt()
{
	// Set up Watch Dog Timer for Inactivity
	WDTCR |= ((1 << WDCE) | (1 << WDE));    // Enable the WD Change Bit
	WDTCR  = (1 << WDIE) |               	// Enable WDT Interrupt
           	 (1 << WDP3);     				// Set Timeout to ~4 seconds
}

void init_wdt_05s()
{
	// Set up Watch Dog Timer for Inactivity
	WDTCR |= ((1 << WDCE) | (1 << WDE));    // Enable the WD Change Bit
	WDTCR  =  (1 << WDIE) |               	// Enable WDT Interrupt
           	  (1 << WDP0) | (1 << WDP2);    // Set Timeout to ~0.5 seconds
}

void sleep_avr()
{
	// Disable analog to digital converter
	disable_adc();

	set_sleep_mode(SLEEP_MODE_PWR_DOWN);    // replaces above statement
	cli();
	sleep_enable();                         // Sets the Sleep Enable bit in the MCUCR Register (SE BIT)
	sei();                                  // Enable interrupts
	sleep_cpu();                            // sleep
	sleep_disable();                        // Disable interrupts

	// Enable global interrupts
	sei(); 
}

/*
Port B Data Direction Register (controls the mode of all pins within port B)
DDRB is 8 bits: [unused:unused:DDB5:DDB4:DDB3:DDB2:DDB1:DDB0]
*/
void init_pins()
{
	// LED PIN
	DDRB = (1 << LED_PIN);
}

void blink()
{
	PORTB ^= (1 << LED_PIN);
	_delay_ms(LED_DURATION);
	PORTB ^= (1 << LED_PIN);
}

void dsp(long val)
{
	// subtract the last reading:
	total = total - readings[reading_index];
	
	// read from the sensor:
	readings[reading_index] = val;
	
	// add the reading to the total:
	total = total + readings[reading_index];
	
	// advance to the next position in the array:
	reading_index = reading_index + 1;

	// if we're at the end of the array...
	if (reading_index >= MAX_READINGS) reading_index = 0;

	// calculate the average:
  	average = total / MAX_READINGS;
}

ISR(WDT_vect)
{
}

int main ()
{
	// Disable the ADC
	disable_adc();

	// Watchdog timer reset safety check
	wdt_reset_safety();
	
	// Initialise watchdog timer
	init_wdt();

	// Identify input and output pins
	init_pins();

	// Buffer for text
	char s[20];

	// Setup direction and port for debug logging
	util_init();

	// Initialise DSP
	int i = 0;
	for (; i < MAX_READINGS; i++) readings[i] = 0;

	// Init status
	blink();

	for (;;)
	{
		// Go to sleep
		sleep_avr();
		
		// Read VCC and convert to base 10 number
		long vcc = read_vcc();
		utoa(vcc, s, 10);
		sputs("VCC: ");
		sputs(s);
		sputs("\n\r");

		dsp(vcc);
		sputs("AVG: ");
		utoa(average, s, 10);

		// Output VCC to soft serial PIN STX_BIT
		sputs(s);
		sputs("\n\r");

		if (vcc > FULL_CHARGE_MV)
		{
			// init_wdt_05s();
			blink();
		}
		else init_wdt();	
	}
}