ATtiny13 – randomly flashing LED with PRNG based on BBS

This project is very similar to ATtiny13 – randomly flashing LED with PRNG based on LFSR. However, this time I used BBS (Blum-Blum-Shumb) algorithm as PRNG (Pseudo Random Number Generator) to generate 16-bit (pseudo) random numbers. The less significant bit of randomly generated number is a major factor in decision to on/off the LED. The code is on Github, click here

Parts Required

• ATtiny13  – i.e. MBAVR-1 development board
• Resistor – 220Ω, see LED Resistor Calculator
• LED

Circuit Diagram

Software

This code is written in C and can be compiled using the avr-gcc. All information about how to compile this project is here.

/**
 * Copyright (c) 2019, Łukasz Marcin Podkalicki <lpodkalicki@gmail.com>
 * ATtiny13/048
 * Randomly flashing LED with PRNG based on BBS (Blum-Blum-Shumb).
 */

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

#define LED_PIN PB0
#define BBS_P (13)
#define BBS_Q (97)
#define BBS_SEED (123)
#define DELAY (64)

static uint16_t m;
static uint16_t x;
static uint16_t r;

/* Initialize vector of BBS algorithm, where:
-> p: prime number
-> q: prime number
-> seed: random integer greater then 1,
 which is co-prime to 'm',
 where 'm = p*q' and 'GCD(m, seed) == 1'
Note that value of 'm' must be less than '(2^16) - 1'
*/
static void
bbs_init(uint16_t p, uint16_t q, uint16_t seed)
{

    m = p * q;
    r = x = seed;
}

static uint16_t
bbs_next(void)
{

    return (r = (r * x) % m);
}


int
main(void)
{

    /* setup */
    DDRB |= _BV(LED_PIN); // set LED pin as OUTPUT
    bbs_init(BBS_P, BBS_Q, BBS_SEED); // initialize BBS alg.

    /* loop */
    while (1) {
        if (bbs_next() & 1) {
            PORTB |= _BV(LED_PIN);
        } else {
            PORTB &= ~_BV(LED_PIN);
        }
        _delay_ms(DELAY);
    }
}