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// ************************************************************
// ** Spektrum Diversity - use up to 4 satellite receivers   **
// ************************************************************
// ** Target: An Atmel ATtiny2313 (RC-Oscillator @ 8 MHz)    **
// **         controls a 74HC151 Multiplexer                 **
// ************************************************************
// ** It monitors the data from 4 satellite receivers and    **
// ** connects a valid one to the output via the multiplexer **
// ************************************************************
// ** LED-Modes during startup (in chronological order)      **
// ** ************************                               **
// ** LED fast blink: Waiting for first datapulse            **
// ** LED slow blink: Waiting 3 seconds while counting sat's **
// ** LED flashes: Indicates the number of active sat's      **
// **                                                        **
// ** LED-Modes during operation                             **
// ** **************************                             **
// ** LED OFF: Everything is fine                            **
// ** LED ON: FAILURE - The first selected sat had lost sync **
// ************************************************************
// ** (c) 2010-0xFFFF Stefan Pendsa                          **
// ** License: don't know - use it and have fun              **
// ************************************************************

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>

#define LED_OFF PORTD |= 1 << PORTD0
#define LED_ON  PORTD &= ~(1 << PORTD0)

volatile unsigned int TimerEvent;


void SelectSat(unsigned char sat)
{
        PORTD = (PORTD & 0b00000001) | (sat<<3);                                // Select the Input for 74HC151
}

void ResetTimer(void)
{
        TCNT1H = 0;
        TCNT1L = 0;
        TimerEvent = 0;
}


void Binding(void)                                                                                      // Binding sequence for DX7
{
        unsigned char i = 0;

        DDRB = 0b11110000;                                                                              // Sat-Pins to output
        _delay_ms(80);                                                                                  // Let them boot up
        
        for (i=0;i<3;i++)                                                                               // send three negative 100µs pulses to all sat's
        {
                PORTB = 0b00000000;
                _delay_us(100);
                PORTB = 0b11110000;
                _delay_us(100);
        }

        _delay_ms(1000);
        DDRB = 0b00000000;                                                                              // Sat-Pins to input after 1sec
}


void Testing(void)                                                                                      // Self Test
{
        unsigned char i = 0;
        unsigned char error = 0;

        DDRB = 0b11110000;                                                                              // PORT B OUTPUT FOR SATELLITES, INPUT FOR FEEDBACK
        PORTB = 0b00000000;

        for(i=0;i<4;i++)                                                                                // Test muxxing of High+Low on every Sat-Input
        {
                SelectSat(i);
                PORTB |= 1 << (i+4);
                if (!(PINB & (1<<PB3))) error++;
                PORTB &= ~(1 << (i+4));
                if (PINB & (1<<PB3)) error++;
        }

        while(1)                                                                                                // Never return
        {
                if (error == 0)                                                                         // When no error occured, flash around
                {
                        LED_ON;
                        _delay_ms(100);
                        LED_OFF;
                        _delay_ms(100);
                }
        }
}


ISR(TIMER1_OVF_vect)                                                                            // Triggered every 8,192 msec
{
        TimerEvent++;
}


int main(void)
{
        unsigned char i = 0;
        unsigned char j = 0;
        unsigned char active[4];
        unsigned char sat = 4;

        DDRB = 0b00000000;                                                                              // PORT B INPUT FOR SATELLITES AND FEEDBACK
        DDRD = 0b0011001;                                                                               // PORT D OUTPUT FOR MUX AND LED, INPUT FOR SWITCH & TEST
        PORTB = 0b11110000;                                                                             // PORT B PULLUP's FOR (unused) SATELLITES
        PORTD = 0b1100001;                                                                              // PORT D PULLUP's FOR SWITCH & TEST

        for (i=0;i<4;i++) active[i] = 0;                                                // Reset active-array

        if (!(PIND & (1<<PD6))) Binding();                                              // Initiate Binding when Bind-Button is pressed
        if (!(PIND & (1<<PD5))) Testing();                                              // Initiate Self-Test when Test-Pad is low

        TCCR1B = ( 1 << CS10 );                                                                 // Timer1 Prescaler = 1 -> 8,192 msec
        TIMSK = ( 1 << TOIE1 );                                                                 // Timer1 Overflow Interrupt Enable
        sei();                                                                                                  // Global Interrupts enable

        ResetTimer();
        while((PINB & 0b11110000) == 0b11110000)                                // Wait for first signal (SYNC to frame)
        {
                if (TimerEvent == 10) LED_ON;                                           // Blink while waiting...
                if (TimerEvent == 20)
                {
                        LED_OFF;
                        TimerEvent = 0;
                }
        }

        LED_OFF;

        ResetTimer();
        while(1)                                                                                                // Check active satellites for 3 seconds
        {
                if (TimerEvent == 20) LED_ON;                                           // Blink (slower) while waiting...
                if (TimerEvent == 40)
                {
                        LED_OFF;
                        TimerEvent = 0;
                        j++;
                }

                for (i=0;i<4;i++)
                {
                        if (!(PINB & (1<<(i+4))))
                        {
                                active[i] = 1;
                                if (sat == 4)                                                           // Select first active satellite (only once)
                                {
                                        sat = i;
                                        SelectSat(i);
                                }

                        }
                }
                
                if (j == 9) break;                                                                      // 9 * 40 * 8ms = ~3sec
        }

        LED_OFF;
        _delay_ms(1000);

        for (i=0;i<4;i++)                                                                               // Flash once for every active satellite
        {
                if (active[i] == 1)
                {
                        LED_ON;
                        _delay_ms(100);
                        LED_OFF;
                        _delay_ms(200);
                }
        }




        while(1)                                                                                                // Main-Loop
        {
                ResetTimer();

                while((PINB & 0b11110000) == 0b11110000)                        // Wait for first signal (SYNC to frame)
                {
                        if (TimerEvent > 3) break;                                              // (max. 3*8=24ms)
                }
                
                for (i=0;i<4;i++) active[i] = 0;                                        // Reset active-array
                ResetTimer();

                while(TimerEvent < 1)                                                           // Check active satellites (for 1*8=8ms)
                {

                        for (i=0;i<4;i++)
                        {
                                if (!(PINB & (1<<(i+4))))
                                {
                                        active[i] = 1;
                                }
                        }
                }


                if (active[sat] == 0)                                                           // Detect fail on active satellite
                {
                        LED_ON;                                                                                 // Failure-LED ON (never goes off again)
                        for (i=0;i<4;i++)                                                               // Select lowest active satellite
                        {
                                if (active[i] == 1)
                                {
                                        sat = i;
                                        SelectSat(sat);
                                        break;
                                }
                        }
                }


        }

}