ATMEGA328P external interrupt avr gcc won't happen - gcc

Question

An external interrupt vector should occur when a 5v input is supplied to int0.
The interrupt should change a volatile integer flag to allow a LED to illuminate that is connected to a pin on PORTB. Compiles with no errors in Atmel studio. The problem is no change occurs when a 5v supply is sent to the int0 pin. Is this that the interrupt is not triggering?
#include <avr/io.h>
#include <stdio.h>
#define F_CPU 16000000UL
#include <util/delay.h>
#include <avr/interrupt.h>
volatile int pwm_flag=0;
int main(void)
{
DDRD &= ~(1 << DDD2); // Clear the PD2 pin
// PD2 (PCINT0 pin) is now an input
PORTD |= (1 << PORTD2); // turn On the Pull-up
// PD2 is now an input with pull-up enabled
EICRA |= (1 << ISC00)|(1 << ISC10); // set INT0 to trigger on Rising edge
EIMSK |= (1 << INT0); // Turns on INT0
sei(); // turn on interrupts
DDRB = 0xFF;
PORTB = 0x00;
while(1)
{
if(pwm_flag==1)//if flag is raised
{
PORTB = 0xFF;//turn on all pins of portb
pwm_flag=0;//reset flag to 0
}
}
}
ISR (INT0_vect)
{
/* interrupt code here */
pwm_flag =1;//raise flag
}

Answer 1

The problem is no change occurs when a 5v supply is sent to the int0 pin.
How do you send 5V to the INT0 pin? Your code is setting INT0 pin as an input with pullup so unless you short it to the ground it is at 5V.
Also, what do you mean by no change occurs? Is the LED on or off?
Another thing is that the line:
EICRA |= (1 << ISC00)|(1 << ISC10);
sets both INT0 and INT1 to occur on any logical change on appropriate pin. Bits with name ISC0x control INT0, bits called ISC1x are used to configure INT1. In your code you are mixing both and you end up with the following configuration:
ISC01 | ISC00 | meaning
-------------------------------------------------------------------------
0 | 1 | any logical change on INT0 generates an interrupt request
ISC11 | ISC10 | meaning
-------------------------------------------------------------------------
0 | 1 | any logical change on INT1 generates an interrupt request

Answer 2

If you are trying to supply 5v from a pin on PORTB to an LED then perhaps that is your problem. Most micro-controller pins can sink more current than they can give. Perhaps your LED is just not getting the current it needs?
Your wiring should be as follows:
Connect the positive leg of the LED to 5V. Connect the negative leg to a small resistor 100-500 Ohms. Connect the other leg of the resistor to the pin on PORTB.
Now you can write PORTB to 0x00 to turn on the LED or 0xFF to turn it off.
To test that the LED is working test the LED in your main loop by writing PORTB low and high with a noticeable delay in between.
If that works. Then test your ISR. If the ISR doesn't work a this point then the ISR is the problem.
Bear in mind that in your current configuration of EICRA you are triggering an interrupt on a rising edge. So if the pin is already high not interrupt will occur.
I have changed your code below so LOW is ON and HIGH is OFF.
int main(void){
DDRD &= ~(1 << DDD2); // set PD2 DDR as input
PORTD |= (1 << PORTD2); // set PD2 as input pull-up
EICRA |= (1 << ISC00)|(1 << ISC10); // set INT0 to trigger on rising edge
EIMSK |= (1 << INT0); // Turns on INT0
DDRB = 0xFF; // set PORTB as all outputs
PORTB = 0xFF; // set PORTB high
sei(); // turn on interrupts
while(1){
if(pwm_flag!=0){ // check flag
PORTB = 0x00; // set PORTB low
pwm_flag=0; // reset flag
}
}
ISR (INT0_vect){
pwm_flag = 1; // raise flag
}