/*

FUSES:

  Low Fuse:
    0x62    Default
    0xC0    External Oscillator, BOD (write lfuse 0 0xC0)
    0xF7    Full Swing Crystal Oscillator (write lfuse 0 0xF7)
    0xFF    Low Power Crystal Oscillator (untested)

  High Fuse
    0xDF    Default
    0xDC    BOD enabled (4.3V)
    0xCF    watchdog enabled
    0xCC    BOD enabled (4.3V) and watchdog enabled

  Extended Fuse
    0x01    Default

  avrdude -c stk500 -P /dev/ttyS0 -p atmega88 -U flash:w:upper-tank-sensor.srec
  avrdude -c usbasp -p atmega168p -U flash:w:upper-tank-sensor.srec

  avrdude -c stk500 -P /dev/ttyS0 -p atmega88 -t
  avrdude -c usbasp -p atmega168p -t
    dump lfuse 0 1
        write lfuse 0 <value>




PINS:
 AVR  Conn   Functions       Usage
   1  P10-3  PD3  OC2B       
   2  P4-13  PD4             
   3         GND
   4         VCC
   5         GND
   6         VCC
   7         PB6  XTAL1      crystal
   8         PB7  XTAL2      crystal
   9  P8-3   PD5  OC0B       
  10  P6-3   PD6  OC0A       
  11  P4-14  PD7  AIN1
  12  P2-6   PB0  ICP1       
  13  P2-4   PB1  OC1A       
  14  P2-5   PB2  OC1B       
  15  P1-4   PB3  MOSI/OC2A  ISP
  16  P1-1   PB4  MISO       ISP
  17  P1-3   PB5  SCK        ISP
  18         AVCC
  19  P4-4   ADC6            
  20  P4-5   AREF
  21         GND
  22  P4-6   ADC7            
  23  P4-7   PC0  ADC0       lower sensor
  24  P4-8   PC1  ADC1       higher sensor
  25  P4-9   PC2  ADC2       overflow sensor
  26  P4-10  PC3  ADC3       
  27  P4-11  PC4  ADC4       
  28  P4-12  PC5  ADC5       
  29  P1-5   PC6  /RESET     ISP
  30         PD0  RXD        RS485 RX
  31         PD1  TXD        RS485 TX
  32         PD2             RS485 driver enable


*/

#define F_CPU				18432000

#include <inttypes.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
#include <tal/prng.h>
#include <tal/usart_funcs.h>

#define SENSOR_VALUE_COUNT	8
#define DELAY				125
#define BAUD_RATE			9600

typedef struct {
	uint8_t sensor_state;
	uint8_t sensor_value_latest;
	uint8_t sensor_values[SENSOR_VALUE_COUNT];
} data_t;

static data_t data;

static void initialize()
{
	int8_t i;

	data.sensor_state = 0;
	data.sensor_value_latest = 0;
	for( i=SENSOR_VALUE_COUNT-1; i>=0; i-- )
	{
		data.sensor_values[i] = 0;
	}

	// timer 2: Fast PWM, Top=OCR2A, clock/1024, overflow @ 125Hz
	TCCR2A = (1<<WGM21) | (1<<WGM20);
	TCCR2B = (1<<WGM22) | (1<<CS22) | (1<<CS21) | (1<<CS20);
	OCR2A = 144-1;

	usart_init( USART_BAUD_RATE(BAUD_RATE) );

	// enable driver and TXD outputs
	DDRD |= (1<<PD2) | (1<<PD1);
	// always enable driver
	PORTD |= (1<<PD2);
}

static uint8_t timer2overflow()
{
	uint8_t v = TIFR2 & (1<<TOV2);
	TIFR2 = v;
	return v;
}

static uint8_t timing()
{
	uint8_t sensors;
	uint8_t sensors_on;
	uint8_t sensors_off;
	int8_t i;

	if( !timer2overflow() )
	{
		return 0;
	}
	sensors = PINC | 0xC0;
	sensors_on = ~sensors;
	sensors_off = sensors;
	for( i=SENSOR_VALUE_COUNT-1; i>=0; i-- )
	{
		sensors_on &= ~data.sensor_values[i];
		sensors_off &= data.sensor_values[i];
	}
	data.sensor_values[data.sensor_value_latest] = sensors;
	data.sensor_value_latest++;
	if( data.sensor_value_latest >= SENSOR_VALUE_COUNT )
	{
		data.sensor_value_latest = 0;
	}
	data.sensor_state = (data.sensor_state & ~sensors_off) | sensors_on;
	return 1;
}

static void send_data( uint8_t counter)
{
	uint16_t checksum;

	xorshift16_init( XORSHIFT16_INIT_DEFAULT );
	xorshift16_next();
	xorshift16_add( counter );
	usart_add_byte( counter );
	usart_add_byte( ~counter );
	xorshift16_next();
	xorshift16_add( data.sensor_state );
	usart_add_byte( data.sensor_state );
	usart_add_byte( ~data.sensor_state );
	xorshift16_next();
	checksum = xorshift16_get_state();
	usart_add_byte( checksum );
	usart_add_byte( checksum>>8 );
}

int main()
{
	uint8_t delay = DELAY;
	uint8_t counter = 0;

	initialize();
	while( 1 )
	{
		if( timing() )
		{
			delay--;
			if( delay == 0 )
			{
				delay = DELAY;
				send_data( counter++ );
			}
		}
		usart_send();
	}
}