#include <avr/io.h>

#include "lights.h"

#define RESISTOR_HI	1500	// kOhm
#define RESISTOR_LO	 100	// kOhm

volatile unsigned char battery_100mv = 0;

void init_battery()
{
	battery_100mv = 0;
}

void battery_adc(uint16_t adcval)
{
	/*
	 * This is tricky: we need to maintain precision, so we first
	 * multiply adcval by as big number as possible to fit uint16_t,
	 * then divide to get the final value,
	 * and finally type-cast it to unsigned char.
	 * We don't do running average, as the required precision
	 * is coarse (0.1 V).
	 */
	battery_100mv = (unsigned char)
		((uint16_t)(adcval * 11                              // 1.1V
		* (RESISTOR_HI+RESISTOR_LO)/RESISTOR_LO    // resistor ratio
		/ 4) >> 8);                                // divide by 1024
}