Serial.println() not working in ISR

Question

Please refer my below code,

const int led_pin = PB5;
const uint16_t t1_load = 0;
const uint16_t t1_comp = 43750;
int blinkcount;
void setup() {
 // put your setup code here, to run once:
 DDRB |= (1<< led_pin);
 TCCR1A = 0;
 //TCCR1B = 0X03;
 TCCR1B |= (1 << CS12);
 TCCR1B &= ~(1 << CS11);
 TCCR1B &= ~(1 << CS10);
 TCNT1 = t1_load;
 OCR1A = t1_comp;
 TIMSK1 = (1 << OCIE1A);
 Serial.begin(9600);
 sei();
}
void loop() {
 // put your main code here, to run repeatedly:
 delay(500);
}
ISR(TIMER1_COMPA_vect) {
 TCNT1 = t1_load;
 PORTB ^= (1 << led_pin);
 blinkcount = blinkcount + 1;
 Serial.println(blinkcount);
}

the Serial.println(blinkcount); not working or the serial window does not show up.

Apologies if it sound stupid as I'm new to programming.

• jsotola: please format your code .... you don't print inside ISR .... increment variable and set a second flag variable instead ... check for flag in loop() and print if the flag is set
• Fatpanda: @jsotola can you please review the changed code and share your suggestion?

Answer 1

ISR are simply not intended for this abuse.

If you want to use Arduino level functions, you must have good reasons why you need to mix them with direct arv-gcc hardware-accessing code (or vice versa).

If you're new to programming and to Arduino, simply ignore that level (for now).

DDRB |= BV(PB5); is easier understandable if you write

pinMode(13,OUTPUT); ( or even use LED_BUILTIN instead of 13 )

Answer 2

const uint16_t t1_load = 0;
const uint16_t t1_comp = 43750;
int blinkcount;
int flag, flag_1, a, i;
void setup() {
 // put your setup code here, to run once:
 DDRB |= (1<< led_pin);
 TCCR1A = 0;
 //TCCR1B = 0X03;
 TCCR1B |= (1 << CS12); //for 256 prescalar
 TCCR1B &= ~(1 << CS11);
 TCCR1B &= ~(1 << CS10);
/* TCCR1B &= ~ (1 << CS12);
 TCCR1B |= (1 << CS11);
 TCCR1B &= ~(1 << CS10);*/
 TCNT1 = t1_load;
 OCR1A = t1_comp;
 TIMSK1 = (1 << OCIE1A);
 Serial.begin(9600);
 sei();
}
void loop() {
 // put your main code here, to run repeatedly:
 delay(500);
/* blinkcount = blinkcount + 1;
 if(blinkcount++)
 {
 flag = 1;
 }
 if(flag == 1)
 {
 Serial.println("ok");
 }*/
}
void loop_1()
{
 i = blinkcount;
 //for(i=0; i<=blinkcount; i++);
 //{
 i = i + 1;
 //if(i++)
 // {
 flag = 1;
 flag_1 = flag;
 //}
 if(flag_1 == 1)
 {
 Serial.println(flag_1);
 }
// }
}
ISR(TIMER1_COMPA_vect) {
 TCNT1 = t1_load;
 PORTB ^= (1 << led_pin);
 //blinkcount = blinkcount + 1;
 //Serial.println(blinkcount);
 loop_1();
}```
I've changed the code according to your suggestion, the tx led on arduino blinks but serial monitor does not pop up

• DataFiddler: loop_1 is (logically) still part of the ISR. Serial.println() not working in ISR is a fact, not a question. Don't use ISRs if you don't need OR understand it. In your case both conditions apply. Sorry.