#include <avr/io.h>
#include <avr/sleep.h>

#include <stdint.h>

int main()
{
	uint8_t input;
	uint8_t temp;
	uint8_t count;
	uint8_t i;

	// Setup
	PORTA = (1 << PORTA7) | (1 << PORTA6) | (1 << PORTA5) | (1 << PORTA4);
	DDRA = (1 << DDA7) | (1 << DDA6) | (1 << DDA5) | (1 << DDA4);
	PORTB = (1 << PORTB2);
	DDRB = (1 << DDB2);
	PRR = (1 << PRTIM1) | (1 << PRTIM0) | (1 << PRUSI) | (1 << PRADC);

	// Read Inputs
	input = PINA;
	temp = input;
	count = 0;

	// How many inputs are set
	for (i = 0; i < 4; ++i)
	{
		if (temp & 0x01)
		{
			++count;
		}
		temp >>= 1;
	}

	// If none or more than 1 are providing power - do nothing until reboot
	if (count != 1)
	{
		goto end;
	}

	// Set Upstream Facing Port
	input = ~input;
	input <<= 4;
	PORTA = input;
	PORTB &= ~(1 << PORTB2);

end:
	// Power Down Mode
	MCUCR = (1 << SM1) | (1 << SE);
	while (1)
	{
		sleep_cpu();
	}
}