Sketch size and different Datatypes makes no difference? (for ATTiny)

Using Arduino Microcontrollers
1

I'm playing around with different Attinys and I try to adapt my sketch and observe if I can shrink down the size of my source code.

int led1 = 4;

void setup() {

  pinMode(led1, OUTPUT);

}

void loop() {
  analogWrite(led1, 15);
}

This Source code uses 1392 bytes, nevertheless if I set the led1 to int, long, byte or what else?

I thought in coding with MCU it is critical which data types I'm using?

Thanks for your help

2

Perhaps the compiler can see that the variable led1 is never updated, so it optimises it as a constant requiring only 1 byte. It would do this no matter what type byte/int/long you make it.

Try

volatile int led1 = 4;

and then change the int to byte or long. The volatile keyword tells the compiler not to make assumptions/optimisations about the variable, but the compiler might still not be fooled by that, I don't know.

2 Likes
3

No way.

4

Why not? Do I mix here something up?

Without analogWrite and a few more LEDs the Sketch uses 912 bytes?

image
image1724×808 35.6 KB

5

You're confusing source and object.

6

The optimizer really does it's best for you, but to see effects you will need a more expanded program than what you are doing now. Even if the compiler doesn't see it as a constant, it will know where it is used, and if it is used as an argument for a function that takes a 16 or 8 bit value, the variable will get truncated to that unless it is modified somewhere.
Reducing variable sizes can make a huge difference, for instance if you use millis() but can make do with a 16-bit value, do so !
Avoid floating point variables since using them requires the use of special functions that will need to be compiled.
If you define something like

#define ECHO 14
#define VALUE 23 * ECHO + 12

you will find that when using VALUE somewhere, you can reduce flash by adding braces

#define (VALUE 23 * ECHO + 12)

Forcing the compiler to do the calculation instead of the MCU from within the sketch.

1 Like
7

Please post the code you are trying to use (within code tags </> no screenshot !) and the board you are compiling for (and the core you are using)
So i can re-create and show you how it does work.

1 Like
8

Thank you very much for your explanation. Makes sense!

I have no specific problem to discus. I just want to understand the principial how to shrink the source code size.

Now I have better understanding.
Have a nice day!

9

Fixed.

10

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