I’ve been testing some buzzer functions on an ATtiny85 and I noticed a weird flash memory usage fluctuation when changing constant arguments of a function.
In more detail, compiling the following code the memory occupied is 162 bytes
int main(){
beep_once(1000,500);
silence(1000);
beep_once(1000,500);
silence(200);
for(;;){ }
}
While just changing the first beep_once(1000,500); to beep_once(1500,500); the program size becomes 1378 bytes.
Using the memory inspection by PlatformIO, I can see that c. 1kb of memory is due to unknown. What does it mean?
Hope someone can help me understand what is going on and what side is the problem: PlatformIO, compiler or it’s me.
Here the full code used for the test:
#include <avr/interrupt.h>
#define F_CLK 1000000
void silence(unsigned int);
void beep_once(unsigned int, unsigned int);
int main(){
beep_once(1500,500);
silence(1000);
beep_once(1000,500);
silence(200);
for(;;){ }
}
void silence(unsigned int duration)
{
TCCR1 = 5; // Set the prescaler to 16 bit.
OCR1A = 61; // Tops at 1ms with prescaler of 16x
unsigned int counter=duration;
do
{
if ((TIFR >> OCF1A) & 0x01)
{
counter--;
TCNT1 = 0; // Reset counter to 0
TIFR |= 1 << OCF1A; // Clear the flag
}
} while (counter);
TCCR1 &= ~((1 << CS12) | (1 << CS11) | (1 << CS10)); // Stop the timer
}
void beep_once(unsigned int frequency /*Herz*/, const unsigned int duration /*milliseconds*/)
{
/*
* The frequency is given by:
* Freq = F_CLK / (prescaler * (1 + OCR1C))
*/
TCCR1 |= (5 << CS10) |(1 << CTC1); // Set the prescaler to 16 bit (for 1MHz)(freq range from 31kHz to 250 Hz)
OCR1C = (uint8_t)((F_CLK / frequency) >> 5); // divided by the prescaler (16)
TIMSK &= ~(1 << OCIE1B); // Disable timer compare interrupt
GTCCR |= 1 << COM1B0; // Timer Counter Comparator B connected to output pin OC1B.
unsigned int counter = duration * ((float)frequency / 1000.) * 2;;
do
{
if ((TIFR >> OCF1B) & 0x01)
{
counter--;
TIFR |= 1 << OCF1A; // Clear the flag
}
} while (counter);
TCCR1 &= ~((1 << CS12) | (1 << CS11) | (1 << CS10)); // Stop the timer
GTCCR &= ~(1 << COM1B0); // Timer Counter Comparator B disconnected from output pin OC1B.
}
You can however just write 