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// ************************************************************
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// ** Spektrum Diversity - use up to 8 satellite receivers   **
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// ************************************************************
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// ** Target: An Atmel ATtiny2313 (RC-Oscillator @ 8 MHz)    **
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// **         controls a 74HC151 Multiplexer                 **
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// ************************************************************
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// ** It monitors the data from 8 satellite receivers and    **
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// ** connects a valid one to the output via the multiplexer **
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// ************************************************************
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// ** LED-Modes during startup (in chronological order)      **
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// ** ************************                               **
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// ** LED fast blink: Waiting for first datapulse            **
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// ** LED slow blink: Waiting 3 seconds while counting sat's **
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// ** LED flashes: Indicates the number of active sat's      **
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// **                                                        **
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// ** LED-Modes during operation                             **
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// ** **************************                             **
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// ** LED OFF: Everything is fine                            **
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// ** LED ON: FAILURE - The first selected sat had lost sync **
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// ************************************************************
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// ** (c) 2010-0xFFFF Stefan Pendsa                          **
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// ** License: don't know - use it and have fun              **
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// ************************************************************
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#include <util/delay.h>
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#define LED_OFF	PORTD |= 1 << PORTD3
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#define LED_ON	PORTD &= ~(1 << PORTD3)
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volatile unsigned int TimerEvent;
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void SelectSat(unsigned char sat)
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{
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	/*
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	Re-Assignment due to easier routing on layout: sat -> mux-channel# -> mux-input (seen from µC)
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	1 -> 1 -> 4
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	2 -> 0 -> 0
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	3 -> 3 -> 6
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	4 -> 4 -> 1
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	5 -> 5 -> 5
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	6 -> 6 -> 3
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	7 -> 7 -> 7
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	*/
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	if (sat == 0) sat = 2;
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	else if (sat == 1) sat = 4;
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	else if (sat == 2) sat = 0;
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	else if (sat == 3) sat = 6;
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	else if (sat == 4) sat = 1;
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	else if (sat == 5) sat = 5;
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	else if (sat == 6) sat = 3;
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	else if (sat == 7) sat = 7;
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	PORTD = (PORTD & 0b00001000) | sat;
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}
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void ResetTimer(void)
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{
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	TCNT1H = 0;
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	TCNT1L = 0;
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	TimerEvent = 0;
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}
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ISR(TIMER1_OVF_vect)										// Triggered every 4,096 msec
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{
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	TimerEvent++;
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}
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int main(void)
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{
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	unsigned char i = 0;
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	unsigned int j = 0;
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	unsigned char active[8];
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	unsigned char sat = 9;
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	DDRB = 0b00000000;										// PORT A INPUT FOR SATELLITES
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	DDRD = 0b00001111;										// PORT B OUTPUT FOR MUX AND LED
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	PORTB = 0b11111111;										// PORT A PULLUP's FOR (unused) SATELLITES
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	TCCR1B = ( 1 << CS10 );									// Timer1 Prescaler 1 = 4,096 msec
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	TIMSK = ( 1 << TOIE1 );									// Timer1 Overflow Interrupt Enable
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	sei();													// Global Interrupts enable
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	for (i=0;i<8;i++) active[i] = 0;						// Reset active-array
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	ResetTimer();
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	while(PINB == 255)										// Wait for first signal (SYNC to frame)
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	{
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		if (TimerEvent == 10) LED_ON;						// Blink while waiting...
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		if (TimerEvent == 20)
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		{
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			LED_OFF;
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			TimerEvent = 0;
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		}
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	}
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	LED_OFF;
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	ResetTimer();
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	while(1)												// Check active satellites for 3 seconds
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	{
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		if (TimerEvent == 20) LED_ON;						// Blink (slower) while waiting...
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		if (TimerEvent == 40)
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		{
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			LED_OFF;
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			TimerEvent = 0;
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			j++;
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		}
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		for (i=0;i<8;i++)
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		{
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			if (!(PINB & (1<<i)))
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			{
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				active[i] = 1;
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				if (sat == 9)								// Select first active satellite (only once)
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				{
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					sat = i;
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					SelectSat(i);
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				}
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			}
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		}
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		if (j == 9) break;									// 9 * 40 * 8ms = ~3sec
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	}
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	LED_OFF;
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	_delay_ms(1000);
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	for (i=0;i<8;i++)										// Flash once for every active satellite
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	{
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		if (active[i] == 1)
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		{
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			LED_ON;
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			_delay_ms(200);
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			LED_OFF;
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			_delay_ms(200);
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		}
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	}
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	while(1)												// Main-Loop
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	{
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		ResetTimer();
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		while(PINB == 255)									// Wait for first signal (SYNC to frame)
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		{
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			if (TimerEvent > 3) break;						// (max. 3*8=24ms)
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		}
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		for (i=0;i<8;i++) active[i] = 0;					// Reset active-array
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		ResetTimer();
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		while(TimerEvent < 1)								// Check active satellites (for 1*8=8ms)
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		{
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			for (i=0;i<8;i++)
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			{
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				if (!(PINB & (1<<i)))
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				{
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					active[i] = 1;
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				}
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			}
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		}
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		if (active[sat] == 0)								// Detect fail on active satellite
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		{
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			LED_ON;											// Failure-LED ON (never goes off again)
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			for (i=0;i<8;i++)								// Select lowest active satellite
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			{
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				if (active[i] == 1)
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				{
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					sat = i;
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					SelectSat(sat);
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					break;
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				}
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			}
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		}
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	}
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}