Tone.cpp improvement

Development Libraries
1

Searching through some core code I came across the tone lib and especially the function:

void tone(uint8_t _pin, unsigned int frequency, unsigned long duration)

This function tries to find an optimal prescaler for the timer. To do that it calculates the OCR = F_CPU / frequency / 2 / SomePrescaler -1 nine times.
Because division is expensive I took an extra variable uint32_t ocrRaw = F_CPU / frequency / 2; which is the repeating part of the formula
and replaced that in the rest of the function.

I tested with ToneKeyboard.pde sample sketch to see the impact on the size.
before patch => 3614 bytes
after patch => 3526 bytes
improvement == 88 bytes!

I did not test speed, I expect it to be slightly faster (no free Arduino nearby to test)

Disadvantages?

2

Posted as improvement - memory improvement of the tone.cpp lib · Issue #192 · arduino/ArduinoCore-avr · GitHub -

3

robtillaart:
Searching through some core code I came across the tone lib and especially the function:

void tone(uint8_t _pin, unsigned int frequency, unsigned long duration)

This function tries to find an optimal prescaler for the timer. To do that it calculates the OCR = F_CPU / frequency / 2 / SomePrescaler -1 nine times.
Because division is expensive I took an extra variable uint32_t ocrRaw = F_CPU / frequency / 2; which is the repeating part of the formula
and replaced that in the rest of the function.

I tested with ToneKeyboard.pde sample sketch to see the impact on the size.
before patch => 3614 bytes
after patch => 3526 bytes
improvement == 88 bytes!

I did not test speed, I expect it to be slightly faster (no free Arduino nearby to test)

Disadvantages?

Or, just replace the entire tone library with NewTone and save almost 1200 bytes.

Tim

4

There are always other options, Tim!