/* Soil Sensor Firmware
 * Soil Moisture and Vcc Measurement
 * 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 "moisture.h"
#define F_CPU 2000000UL /* 16Mhz crystal / 8. */
#include "util/delay.h"
#include <util/atomic.h>

/* Disable and shut down power to the ADC. */
static void shutdown_adc(void){
	ADCSRA &= ~_BV(ADEN); /* Disable ADC. */
	PRR |= _BV(PRADC);
}

/* Turn on power to the ADC. */
static void startup_adc(void){
	PRR &= ~_BV(PRADC);
}

/* Initialize the ADC. */
void init_adc(void){
	/* Disable digital inputs to save power. */
	DIDR0 = _BV(7) | _BV(6) | _BV(ADC1D) | _BV(ADC0D);
	ADCSRA = _BV(ADPS2); /* Clk/16 */
	shutdown_adc();
}

/* Get the number of zones on this device.
 * Currently just returns 1. */
uint8_t num_zones(void){
	DDRB &= ~(_BV(PB1) | _BV(PB2));
	PORTB |= _BV(PB1) | _BV(PB2);

	uint8_t z = 4;
// 	if(PINB & _BV(PB1) && PINB & _BV(PB2))z = 1; /* See schematic: X X */
// 	if(PINB & _BV(PB1) && ~(PINB & _BV(PB2)))z = 2; /*             X | */
// 	if(~(PINB & _BV(PB1)) && PINB & _BV(PB2))z = 4; /*             | X */
	
	PORTB &= ~(_BV(PB1) | _BV(PB2));
	DDRB |= _BV(PB1) | _BV(PB2);
	return z;
}

/* Perform an ADC conversion and returns the result. This
 * function blocks until the conversion is complete. */
static uint16_t adc_conversion(void){
	ADCSRA |= _BV(ADEN) | _BV(ADSC); /* Enable ADC and start conversion. */ 
	while(ADCSRA & _BV(ADSC)){
		/* Wait for conversion to finish. */
	}
	
	uint16_t result;
	ATOMIC_BLOCK(ATOMIC_RESTORESTATE){
		result = ADCL;
		result |= (uint16_t) ADCH << 8;
	}
	return result;
}

/* Measure the moisture level of a given zone. 
 * Returns a value between 0 and 2^(10 + OVERSAMPLING_BITS). 
 * Lower values indicate more moisture. */
uint16_t get_moisture(uint8_t zone){
	startup_adc();
	switch(zone){
		/* Rev 5 */
// 		case 0:
// 			ADMUX = 6;
// 			break;
// 		case 1:
// 			ADMUX = 1;
// 			break;
// 		case 2:
// 			ADMUX = 0;
// 			break;
// 		case 3:
// 			ADMUX = 1;
// 			break;
		/* Rev 6 */
		case 0:
			ADMUX = 6;
			break;
		case 1:
			ADMUX = 7;
			break;
		case 2:
			ADMUX = 0;
			break;
		case 3:
			ADMUX = 1;
			break;
	}
	
	ADMUX |= _BV(REFS0); /* Select AVcc as reference. */
	
	adc_conversion(); /* Throw away first result. */
	
	uint32_t value = 0;
	uint32_t total = 0;
	for(int a=0; a < ADC_AVERAGES; a++){
		value = 0;
		for(int s=0; s < (1 << (2 * ADC_OVERSAMPLING_BITS)); s++){
			value += adc_conversion();
		}
		value >>= ADC_OVERSAMPLING_BITS;
		total += value;
	}
	total /= ADC_AVERAGES;
	
	shutdown_adc();
	
	/* Reset peak detector. */
	DDRC |= _BV(PC1) | _BV(PC0);
	DDRE |= _BV(PE3) | _BV(PE2);
	_delay_ms(1);
	DDRC &= ~(_BV(PC1) | _BV(PC0));
	DDRE &= ~(_BV(PE3) | _BV(PE2));
	return total;
	
	/* Improving accuracy/stability of the soil moisture sensor:
	 * (Using multiple zone didn't work, due to the inductance on the signal
	 *  lines beyond the first zone.)
	 * (Note: r5 measurement capacitor minimum capacitance ~3pF.)
	 * Issues:
	 *   -Drift in water content/dielectric constant of PCB (coat with moisture-barrier epoxy)
	 *   -Drift in diode Vf
	 *   -Change in diode Vf with temperature (MASSIVE)
	 *   -(maybe?) Drift in smoothing cap (likely, but shouldn't affect the result)
	 *   -Drift in 100k resistor
	 * All four diodes should be identical and fabricated on the same substrate. Even if they aren't they're
	 * certainly in the same package, so their temperature should match pretty closely.
	 * So, use another channel with a constant capacitance (say 10pF). Measure the output of that channel
	 * and use it to temperature-compensate the moisture measurement(s). */
}
	

/* Measure Vcc.
 * Returns Vcc in 1/32V increments. */
uint16_t get_vcc(void){
	startup_adc();

	_delay_us(100); /* Wait for 1.1V reference to stabilize. */

	ADMUX = 14; /* Measure 1.1V reference. */
	ADMUX |= _BV(REFS0); /* Select AVcc as reference. */
	ADCSRA |= _BV(ADEN) | _BV(ADSC); /* Enable ADC and start conversion. */ 
	
	adc_conversion(); /* Throw away first result. */
	uint16_t result = adc_conversion();
	
	shutdown_adc();
	
	result = 36045 / result; /* (1.1 * 1024 * 32) / result */
	return result;
}