ISR usage guidelines

Development Suggestions for the Arduino Project
1

I had a problem using TIMER2 interrupts, because tone library already
occupies it. Even when I do not include that library. I fixed it by
modifying Tone.cpp code with the weak attribute. Now your code
can reuse the interrupt vector. Of course tone() is now unavailable.
This would be a good practice for all base library ISR vectors.

ISR(TIMER2_COMPA_vect) attribute ((weak));

You can do this by editing and recompiling your project. Arduino IDE
seems to take care of recompilation of the modified tone.cpp
/Applications/Arduino/Contents/Resources/Java/hardware/cores/arduino/Tone.cpp

2

I compiled this sketch fine:

ISR(TIMER2_COMPA_vect) {
    PIND = 0xf0;
}
void setup() {}
void loop() {}

on both 1.0.1 and the newest github version (commit 222d51e3831d77f60ae6ce1f3d037b0febb0c717) with avr-gcc 4.7.1 and avr-libc 1.8.0

What "problems" are you having?

3

Not the OP, but I have also found I cannot redefine ISRs in my sketches, I assumed this was normal, are you suggesting that we should expect to be able to override INT0 etc ?

Duane B

rcarduino.blogspot.com

4

Even with the avr-gcc that gets downloaded with the source (version 4.3.2), this still compiles on my computer:

void setup() {}
void loop() {}
ISR(ADC_vect)               {PIND = 0x00;}
ISR(ANALOG_COMP_vect)       {PIND = 0x01;}
ISR(EE_READY_vect)          {PIND = 0x02;}
ISR(INT0_vect)              {PIND = 0x03;}
ISR(INT1_vect)              {PIND = 0x04;}
ISR(PCINT0_vect)            {PIND = 0x05;}
ISR(PCINT1_vect)            {PIND = 0x06;}
ISR(PCINT2_vect)            {PIND = 0x07;}
ISR(SPI_STC_vect)           {PIND = 0x08;}
ISR(SPM_READY_vect)         {PIND = 0x09;}
ISR(TIMER0_COMPB_vect)      {PIND = 0x0a;}
//ISR(TIMER0_OVF_vect)        {PIND = 0x0b;}
ISR(TIMER1_CAPT_vect)       {PIND = 0x0c;}
ISR(TIMER1_COMPA_vect)      {PIND = 0x0d;}
ISR(TIMER1_COMPB_vect)      {PIND = 0x0e;}
ISR(TIMER1_OVF_vect)        {PIND = 0x0f;}
ISR(TIMER2_OVF_vect)        {PIND = 0x10;}
ISR(TWI_vect)               {PIND = 0x11;}
//ISR(USART_RX_vect)          {PIND = 0x12;}
ISR(USART_TX_vect)          {PIND = 0x13;}
//ISR(USART_UDRE_vect)        {PIND = 0x14;}
ISR(WDT_vect)               {PIND = 0x15;}

The two USART ones didn't work with 4.3.2 but they did with 4.7.1, and the TIMER0_OVF one didn't work on either of them.

It would definitely make sense to make the functions weak. I tried it and it made the above sketch compile with everything uncommented. I think it should be a goal of arduino to be able to use any program that don't use arduino libraries in the IDE, and that means being able to redefine the ISRs.

5

Interestingly, that worked for me as well, I wonder if it was because I was defining the ISR in a cpp file rather than the sketch file ?

Duane B

6

I had problems in compilation using TIMER0_OVF and the following code and was going crazy as it worked ok using the code below:
void setup() {
bitSet(DDRB, 5); // Pin 13 as output
TCCR0A = 0; TCCR0B = 1<<CS02 ; bitSet(TIMSK0, TOIE0);
}
void loop() { }
ISR(TIMER0_OVF_vect) {
bitSet(PINB, 5); // toggle pin 13
}
The error was C:\arduino-1.0\hardware\arduino\cores\arduino/wiring.c:49: multiple definition of `__vector_16'

However, the next lines compile (and run) ok
void setup() {
bitSet(DDRB, 5); // Pin 13 as output
TCCR1A = 0; TCCR1B = 1<<CS12 ; bitSet(TIMSK1, TOIE1);
}
void loop() { }
ISR(TIMER1_OVF_vect) {
bitSet(PINB, 5); // toggle pin 13
}

Now I've seen the comment two posts above ( and the TIMER0_OVF one didn't work on either of them )and felt some relief. Thanks a lot wizenedEE