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#include <avr/io.h> // this contains all the IO port definitions
#include <util/delay.h>
// Global used to store the generated randomness
unsigned int reg=1;
// This function basically wastes time
void delay_ms(long int ms) {
for( ; ms > 0; ms--) {
_delay_ms( 1);
}
}
// Generate one random bit using a feedback shift register
// pseudorandom number generator algorithm
// The coefficients for this came from the TTL Cookbook, Lancaster
void gentick(void) {
int newbit = (((reg>>3)^(reg>>12))^((reg>>14)^(reg>>15)))&1;
reg = (reg<<1) + newbit;
}
int main(void) {
int i;
DDRB = 0xFF; // set port B to output only
PORTB = 0; // turn off all LEDs
while (1) {
// Generate this cycles randomness
for (i=3+8; i; i--) {
gentick();
}
// Flip a random LED
PORTB = PORTB ^ (1<<(reg&7));
// wait a random 0-0.5 seconds
delay_ms(((reg>>3)&0xFF) * 2);
}
}
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