/* 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 "light.h"
#include <util/atomic.h>
#include <stddef.h>
#define F_CPU 2000000
#include "util/delay.h"

#ifndef BREV
#error "No board revision specified. Please provide -DBREV=2 or -DBREV=4 on the command line."
#endif

#if BREV != 2 && BREV != 4 && BREV!=5
#error "Incorect board revision specified. Please provide -DBREV=2, -DBREV=4, or -DBREV=5 on the command line."
#endif

static volatile enum led_state_t LedState, RequestedState;

#if BREV == 2
/* Set the led to a visible state. */
void set_led_visible(enum led_state_t state){
	init_led();
	
	/* Turn the anode on. */
	PORTD |= _BV(PD4);
	
	/* Turn LED off, then selectively turn on the required bits. */
	PORTD |= _BV(PD3);
	PORTE |= _BV(PE0);

	switch (state){
		case(LED_OFF):
			break;
		case(LED_GREEN):
			PORTE &= ~_BV(PE0);
			break;
		case(LED_RED):
			PORTD &= ~_BV(PD3);
			break;
		case(LED_MEASURING):
			break;
	}
}
#elif BREV == 4 || BREV == 5
/* Set the led to a visible state. */
void set_led_visible(enum led_state_t state){
	init_led();
	
	/* Turn the anode on. */
	PORTD |= _BV(PD4);
	
	/* Make the photodiode high impedance. */
	DDRD &= ~_BV(PD3);
	
	if(state == LED_GREEN || state == LED_RED){
		PORTE &= ~_BV(PE0);
	} else {
		PORTE |= _BV(PE0);
	}
}
#endif

/* 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. */
void set_led(enum led_state_t state){
	if(LED_MEASURING == state)return;
	RequestedState = state;
	if(LED_MEASURING != LedState){
		set_led_visible(state);
	}
}

#if BREV == 2
/* Setup pins for the LED. */
void init_led(void){
	DDRD |= _BV(PD4);
	DDRD |= _BV(PD3);
	DDRE |= _BV(PE0);
}
#elif BREV == 4 || BREV == 5
/* Setup pins for the LED. */
void init_led(void){
	DDRD |= _BV(PD4);
	DDRD |= _BV(PD3);
}
#endif


#if BREV == 2

#elif BREV == 4 || BREV == 5

/* Seconds per measure() iteration numerator and denominator. */
#define SPI_N 912ULL
#define SPI_D 130170000ULL

/* Amount of charge moved by photodiode in draining capacitor
 * from 5V to the threshold voltage. */
#define dQ_N  315ULL
#define dQ_D  10000000000ULL

/* Maximum count */
#define MAXC 2000000ULL

/* nA to nW/cm^2 conversion factor. */
#define nA_to_nW 100

/* Measure the time taken for the anode to reach the logic 1 threshold,
 * up to maximum count. */
uint32_t measure(void){
	uint32_t count = 0;
	while(count < MAXC && (PINE & _BV(PE0))){
		count++;
	}
	return count;
}

/* Perform a light measurement. */
uint32_t measure_light(void){
	/* Setup pins: led = hiz, anode = low */
	DDRD &= ~_BV(PD4);
	PORTD &= ~_BV(PD4);
	DDRD |= ~_BV(PD3);
	PORTD &= ~_BV(PD3);
	
	/* Charge cathode to 5V, measure discharge time to 2.5V. */
	PORTE |= _BV(PE0);
	DDRE |= _BV(PE0);
	__builtin_avr_delay_cycles(20);
	DDRE &= ~_BV(PE0);
	PORTE &= ~_BV(PE0);
	uint32_t count = measure();
	PORTE |= _BV(PE0);
	DDRE |= _BV(PE0);
	float A = (3.15e-8/((float)count * (.0912/13017.0)));
	return (uint32_t)(A * 1e9 * 100);
	/* The simple approach in r5 is working pretty well, but it can be improved.
	 * Sources of error (after factory calibration):
	 *   -drift in photodiode sensitivity (unfixable, but unlikely)
	 *   -change (especially increase) in leakage (pot in epoxy, use minimum amount of flux)
	 *   -change in capacitor value (unlikely based on NP0 spec)
	 *   -change in threshold voltage (totally uncontrolled)
	 * Any changes in the threshold voltage cannot be assumed to be consistent among pins.
	 * Therefore, the change in threshold voltage on that pin must be measured. Do this by adding
	 * an extra resistor between a pin and the measurement node (PE0). Usually, the pin is
	 * hi-z, so the resistor doesn't affect the measurement. During a threshold measurement,
	 * the diode is disconnected on its other side with a high-z pin. Then the pin connected
	 * to the resistor is pulled low, and its discharge time is measured. The resistor should
	 * be around 500k. */
}
#endif