/* Soil Sensor Firmware
 * Light Measurement & LED Status Indication
 * Sensiplicity Systems
 * 
 *  Copyright 2015
 * 
 *  Department of Botany and Plant Pathology
 *  Center for Genome Research and Biocomputing
 *  Oregon State University
 *  Corvallis, OR 97331
 * 
 * This program is not free software; you can not redistribute it and/or
 * modify it at all.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. */ 
#include <avr/interrupt.h>

/* This module measures ambient light and provides state indication
 * via the LED on the top of the soil sensor. To measure light,
 * the photodiode is reverse biased, charging the capacitor in parallel with it.
 * The pins connected to it are placed in a high impedance state
 * and the time taken for the photo current to discharge the 
 * capacitor is measured with TIM1. */

/* Set the LED state. This function will only set
 * LED_OFF, LED_RED, and LED_GREEN.
 * This function can be safely called while a measurement is
 * in progress; the state will be set when the measurement is
 * complete. */
enum led_state_t {LED_OFF, LED_RED, LED_GREEN, LED_MEASURING};
void set_led(enum led_state_t state);

/* Setup pins for the LED. */
void init_led(void);

/* Perform a light measurement. This function returns
 * immediately, but the measurement can take up to
 * 260 ms to complete.
 * If result is not NULL, it will be set to the result of the measurement. */
void measure_light(uint16_t volatile *result);

/* Get the result of a previous light measurement.
 * A low value indicates bright light.
 * If no previous measurement is available, or if a measurement
 * is in progress, 0 is returned. */
uint16_t read_light(void);