Why can't I do this:... with IntervalTimer

[ceremona]

void Speak(int pin){
if (count1%2) analogWrite(pin,0); else analogWrite(pin,255); //set the PWM to the just-read sample, this will average out because of the speaker’s inertia to a position
count1++; // increment sample
}

Speak4Timer.begin(Speak, 700);

Compiler gives me hell about not being of type void, but it IS of type void, it's just that the argument to the Speak function isn't a void.

I didn't see anything in the documentation (which is sparse for IntervalTimer) saying I couldn't do this.


Thanks.

 

[PaulStoffregen]

IntervalTimer requires the function to be defined this way:

void Spaek(void)

But your function is:

void Speak(int pin)

IntervalTimer can only call functions which do not take any input. Your's takes an integer.

 

[tni]

IntervalTimer wouldn't know what argument to use for pin when calling "void Speak(int pin)". With C++11 (Arduino 1.6.x), you could use a lambda adapter and write:

const int pin = 7;
Speak4Timer.begin([]{Speak(pin);}, 700);

"pin" must be a compile time constant.

 

[ceremona]

Thanks tni. I'll try this if what your suggesting is true. It's annoying to have to write separate functions for each different pin, when I am only doing the same thing over and over.

So I need to address this as a kind of array like you have it?
Speak4Timer.begin([]{Speak(pin);}, 700);


I already am using a const input as the pin argument but the compiler still balks.

To clarify, I was doing:
const int pin7 = 7;
Speak4Timer.begin(Speak(pin7), 700);

...and it still hated that.

 

[PaulStoffregen]

It's annoying to have to write separate functions for each different pin, when I am only doing the same thing over and over.

Are you aware there are only 4 timers available in the hardware for IntervalTimer to use? At most you'd be writing the same thing 4 times.

 

[tni]

To clarify, I was doing:
const int pin7 = 7;
Speak4Timer.begin(Speak(pin7), 700);

...and it still hated that.

IntervalTimer::begin() takes a function pointer as argument. "Speak(pin7)" is not a function pointer, not even an incompatible one. In "Speak4Timer.begin(Speak(pin7), 700)" the compiler will try to call "Speak(pin7)" which returns "void" and try to use that as argument to "Speak4Timer.begin()" - it can't convert "void" to a function pointer.

"[]{Speak(7);}" is a lambda function and can be transformed by the compiler into a function pointer.

"Speak4Timer.begin([]{Speak(7);}, 700);" is equivalent to:

void adapterFunction() {
    Speak(7);
}
Speak4Timer.begin(adapterFunction, 700);

A lambda function is the easiest way in C++ to get a function pointer to something where you need to pass a parameter. Your "Speak(int)" function is incompatible with "function(void)" (which IntervalTimer expects) and you need an indirection/translation layer.

 

[ceremona]

Thanks tni for that bit of c++ wizardry. I'll store that in my brain somewhere and hope it stays.

Paul. Yes, I know there's only 4 timers, I just wanted to pinch on code space. Also, it seems that there are 4 possible physical FTM channels amongst the pins for the 3.6 teensy (which isn't sadly isn't a huge improvement from 3.2), but what will be the max number of IntervalTimer calls I can make in the code for 3.6?