04 Experiment

Use LFSR based random number generator to generate a random number and display it.

Source and description

http://sincgrid.in/avr-tutorials/avr-tutorial-experiment-4/

http://sincgrid.in/avr-tutorials/avr-tutorial-experiment-4/

#define F_CPU 16000000UL
#include <stdlib.h>
#include <avr/io.h>
#include <util/delay.h>

#define LFSR_SEED       (91)

#define BAUDRATE 9600
#define BAUD_PRESCALLER (((F_CPU / (BAUDRATE * 16UL))) - 1)

uint16_t adc_value;            //Variable used to store the value read from the ADC
char buffer[5];                //Output of the itoa function
uint8_t i=0;                    //Variable for the for() loop

void adc_init(void);            //Function to initialize/configure the ADC
uint16_t read_adc(uint8_t channel);    //Function to read an arbitrary analogic channel/pin
void USART_init(void);            //Function to initialize and configure the USART/serial
void USART_send( unsigned char data);    //Function that sends a char over the serial port
void USART_putstring(char* StringPtr);    //Function that sends a string over the serial port



static uint16_t generate_lfsr_value(void)
{
    static uint16_t cnt16 = LFSR_SEED;
    return (cnt16 = (cnt16 >> 1) ^ (-(cnt16 & 1) & 0xB400));
}

int main(void)
{
    USART_init();        //Setup the USART

    /* loop */
    while (1) {
         uint16_t x= generate_lfsr_value();

        USART_putstring("LFSR value = ");
        itoa(x, buffer, 10);    //Convert the read value to an ascii string
        char *  itoa ( int value, char * str, int base );
        USART_putstring(buffer);        //Send the converted value to the terminal
        USART_putstring("  ");          //Some more formatting
        USART_send('\r');
        USART_send('\n');                //This two lines are to tell to the terminal to change line


    }
    return 0;
}

void adc_init(void){
    ADCSRA |= ((1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0));    //16Mhz/128 = 125Khz the ADC reference clock
    ADMUX |= (1<<REFS0);                //Voltage reference from Avcc (5v)
    ADCSRA |= (1<<ADEN);                //Turn on ADC
    ADCSRA |= (1<<ADSC);                //Do an initial conversion because this one is the slowest
    //and to ensure that everything is up and running
}

uint16_t read_adc(uint8_t channel){
    ADMUX &= 0xF0;                    //Clear the older channel that was read
    ADMUX |= channel;                //Defines the new ADC channel to be read
    ADCSRA |= (1<<ADSC);                //Starts a new conversion
    while(ADCSRA & (1<<ADSC));            //Wait until the conversion is done
    return ADCW;                    //Returns the ADC value of the chosen channel
}

void USART_init(void){
    UBRR0H = (uint8_t)(BAUD_PRESCALLER>>8);
    UBRR0L = (uint8_t)(BAUD_PRESCALLER);
    UCSR0B = (1<<RXEN0)|(1<<TXEN0);
    UCSR0C = (3<<UCSZ00);
}

void USART_send( unsigned char data){

    while(!(UCSR0A & (1<<UDRE0)));
    UDR0 = data;
}

void USART_putstring(char* StringPtr){

    while(*StringPtr != 0x00){
        USART_send(*StringPtr);
    StringPtr++;}

}