Designing a reaction timer for atmega328p microcontroller using C - c

Question

Basic description of what I have to do :
The "reaction timer" is an embedded system that measures the user's reaction time to a signal and displays it in a scale of three LEDs. When the user presses the "ready" pushbutton on the system, the "reaction timer" turns off all LEDs in the system and waits for a random amount of time between 1 and 10 seconds. Upon the expiration of this waiting time, the "reaction timer" turns on a blue LED and signals to the user. The user then presses the "react" pushbutton on the system as quickly as possible to react to the signal. The "reaction timer" then turns off the blue LED used to signal and measures the time elapsed between the signal and the user's reaction to the signal. If the user's reaction time to signal is less than one second, greater than one second but less than two seconds or greater than two seconds, the "reaction timer" turns on a green, orange or a red LED, respectively to display the user's performance.
#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdlib.h> //library includes srand(), rand() methods
#include <time.h> //library include time()
#define F_CPU 4000000UL; //Define F_CPU as 4MHz
int volatile randomnum; //Declare volatile variable for random number generation
int volatile speed; //Declare volatile variable to get the reaction speed
int main(void)
{
DDRB = DDRB | 0b00100111; //Configure PB5,PB0,PB1,PB2 as outputs
DDRD = DDRD & 0b11110011; //Configure PD2(INT0), PD3(INT3) as inputs
PORTD = PORTD | 0b00001100; //Pull-up PD2, PD3
EICRA = (EICRA & 0b11111010) | 0b00001010; //Set external interrupt on falling edge of INT0,INT1
EIMSK = EIMSK | 0b00000011; //Enable external interrupt on INT0,INT1
sei(); //Enable interrupts globally
TCCR1B = (TCCR1B & 0b11111101) | 0b00000101; //Set clock source as F_CPU/1024
TCNT1 = 0; //Default TCNT value as 0
while (1)
{
}
return 0;
}
ISR(INT0_vect){
time_t t; //Declare time variable
PORTB = 0; //Switch off all LEDs
srand( (unsigned) time(&t) ); //Seed the random number using time
randomnum = rand() % 10 + 1; //Generate a random number between 1-10
TCNT1 = ( 65535 - (randomnum * 3906.25) ) + 1; //Assign the value for TCNT to get the delay of random number seconds
TIMSK1 = TIMSK1 | 0b00000001; //Enable timer overflow interrupt
}
ISR(TIMER1_OVF_vect){ //ISR for timer overflow interrupt
PORTB=PORTB|0b00100000; //Switch ON LED connected to PB5
}
ISR(INT1_vect){
speed = TCNT1 / 3906.25; //Calculate the time taken to react
if(speed > 2) //If reaction time greater than 2s
{
PORTB = PORTB | 0b00000100; //Switch ON LED connected to PB2
}
else if ( (speed<2) && (speed>1) ) //If reaction time greater than 1s but less than 2s
{
PORTB = PORTB | 0b00000010; //Switch ON LED connected to PB1
}
else if(speed < 1) //If reaction time less than 1s
{
PORTB = PORTB | 0b00000001; //Switch ON LED connected to PB0
}
}
I have tried to find references on C programs to code embedded system as above. But failed as all those were in arduino.
The above program seems to work only if random number generates as 1. I couldn't find where is the error. Can you please refer my code and point me where the error is?

Answer 1

I think you should clear the overflow flag BEFORE enabling the related interrupt.
Otherwise, if the flag is already set (i.e. about 17 seconds have passed since starting up the program) the interrupt will fire right away.
Please try this, just before enabling the overflow interrupt:
TIFR1 = 0b00000001; // Clear timer overflow flag