ATmega32u4 Timer 3 overflow not functioning - c

Question

I've run into an issue using an ATmega32u4, where I am successfully able to use timer 1 overflows, but when I try to repurpose the code for timer 3, it doesn't function.
The following code turns an LED (on pin b7) on and off when timer 1 (16 bit) overflows. It works.
#include <avr/io.h>
#include <avr/interrupt.h>
int main (void) {
DDRB |= (1<<7);; //PortB Output
PORTB = 0x00; //PortB All LEDs off
TCCR1B |= (1<<CS10) | (1<<CS12); //Set Prescaler to 1024
TIMSK1 |= (1<<TOIE1); //Enable Timer Overflowinterrupt
sei(); //Enable Interrupts
while(1);
return 0;
}
ISR(TIMER1_OVF_vect)
{
PORTB ^= (1<<7); //toggle LED
}
This next code is intended to perform the same functionality using timer 3, but doesn't work.
#include <avr/io.h>
#include <avr/interrupt.h>
int main (void) {
DDRB |= (1<<7);; //PortB Output
PORTB = 0x00;
TCCR3B |= (1<<CS30) | (1<<CS32); //Set prescaler to 1024
TIMSK3 |= (1<<TOIE3); //Enable Timer Overflowinterrupt
sei(); //Enable Interrupts
while(1);
return 0;
}
ISR(TIMER3_OVF_vect)
{
PORTB ^= (1<<7);
}
This final code block was used to test that timer 3's count value was increasing (no interrupts involved), which it is. (I'm using a different LED in this test)
#include <avr/io.h>
int main()
{
// Prescaler of 1024
TCCR3B |= (1<<CS32)|(1<<CS30);
// Initialize Counter
TCNT3 = 0;
// Initialize LED
DDRE |= (1 << 6); // LED0
// Infinite Loop
while (1)
{
// Flash every 0.016 secs
// COUNTER = 0.016 / (PRE SCALER / CPU FREQ)
// 250
if( TCNT3 >= 250 )
{
// Toggle LED
PORTE ^= (1 << 6); // If output use PORT, If input use PIN
TCNT3 = 0;
}
}
return 0;
}
From this, I'm assuming that I'm doing something wrong when calling the interrupt, I'm just not sure what

Answer 1

I am not sure if you are using LilyPad or Leonardo.
I am assuming from the code above that it's LilyPad. Change the TCCR3B to 256 and see if it corrects the problem for you.
TCCR3B = 0x0C; // prescaler = 256