If you use a function after you call it in the same file, you have to (or is better) to add a so called 'forward declaration' before calling it. The best place is before the first function, and in your case it should look like:

void blink(const uint8_t led, int num, const uint16_t l);

You can omit the = 12 or not.

If you use a function after you call it in the same file, you have to (or at least it is better) to add a so called 'forward declaration' before calling it. The best place is before the first function, and in your case it should look like:

void blink(const uint8_t led, int num, const uint16_t l);

You can omit the = 12 or not.