Enthropy.h

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#ifndef RandomSeed_h
#define RandomSeed_h
 
#include "ReelTwo.h"
#include <avr/interrupt.h>
#include <avr/wdt.h>
#include <util/atomic.h>
 
 
volatile uint32_t Enthropy_seed;
volatile int8_t Enthropy_iter;
 
class Enthropy
{
public:
    static uint32_t generate(int8_t iter = 32)
    {
        Enthropy_seed = 0;
        Enthropy_iter = iter;
 
        // Enable watch dog
        setWatchDog(true);
 
        while (Enthropy_iter > 0);
 
        // Disable watch dog
        setWatchDog(false);
 
        return Enthropy_seed;
    }
 
private:
    static void setWatchDog(bool state)
    {
        cli();                                             
        MCUSR = 0;                                         
        _WD_CONTROL_REG |= (1 <<_WD_CHANGE_BIT) | (state << WDE);
        _WD_CONTROL_REG = (state << WDIE);                      
        sei();
    }
};
 
ISR(WDT_vect)
{
    Enthropy_iter--;
    Enthropy_seed = Enthropy_seed << 8;
    Enthropy_seed = Enthropy_seed ^ TCNT1L;
}
 
#endif