Hello, I am trying to understand how the Tone Function on Arduino works. This function allows you to interface a buzzer at certain frequency.
// frequency (in hertz) and duration (in milliseconds).
void tone(uint8_t _pin, unsigned int frequency, unsigned long duration)
{
uint8_t prescalarbits = 0b001;
long toggle_count = 0;
uint32_t ocr = 0;
int8_t _timer;
_timer = toneBegin(_pin);
if (_timer >= 0)
{
// Set the pinMode as OUTPUT
pinMode(_pin, OUTPUT);
// if we are using an 8 bit timer, scan through prescalars to find the best fit
if (_timer == 0 || _timer == 2)
{
ocr = F_CPU / frequency / 2 - 1;
prescalarbits = 0b001; // ck/1: same for both timers
if (ocr > 255)
{
ocr = F_CPU / frequency / 2 / 8 - 1;
prescalarbits = 0b010; // ck/8: same for both timers
if (_timer == 2 && ocr > 255)
{
ocr = F_CPU / frequency / 2 / 32 - 1;
prescalarbits = 0b011;
}
if (ocr > 255)
{
ocr = F_CPU / frequency / 2 / 64 - 1;
prescalarbits = _timer == 0 ? 0b011 : 0b100;
if (_timer == 2 && ocr > 255)
{
ocr = F_CPU / frequency / 2 / 128 - 1;
prescalarbits = 0b101;
}
if (ocr > 255)
{
ocr = F_CPU / frequency / 2 / 256 - 1;
prescalarbits = _timer == 0 ? 0b100 : 0b110;
if (ocr > 255)
{
// can't do any better than /1024
ocr = F_CPU / frequency / 2 / 1024 - 1;
prescalarbits = _timer == 0 ? 0b101 : 0b111;
}
}
}
}
#if defined(TCCR0B)
if (_timer == 0)
{
TCCR0B = (TCCR0B & 0b11111000) | prescalarbits;
}
else
#endif
#if defined(TCCR2B)
{
TCCR2B = (TCCR2B & 0b11111000) | prescalarbits;
}
#else
{
// dummy place holder to make the above ifdefs work
}
#endif
}
else
{
// two choices for the 16 bit timers: ck/1 or ck/64
ocr = F_CPU / frequency / 2 - 1;
prescalarbits = 0b001;
if (ocr > 0xffff)
{
ocr = F_CPU / frequency / 2 / 64 - 1;
prescalarbits = 0b011;
}
if (_timer == 1)
{
#if defined(TCCR1B)
TCCR1B = (TCCR1B & 0b11111000) | prescalarbits;
#endif
}
#if defined(TCCR3B)
else if (_timer == 3)
TCCR3B = (TCCR3B & 0b11111000) | prescalarbits;
#endif
#if defined(TCCR4B)
else if (_timer == 4)
TCCR4B = (TCCR4B & 0b11111000) | prescalarbits;
#endif
#if defined(TCCR5B)
else if (_timer == 5)
TCCR5B = (TCCR5B & 0b11111000) | prescalarbits;
#endif
}
// Calculate the toggle count
if (duration > 0)
{
toggle_count = 2 * frequency * duration / 1000;
}
else
{
toggle_count = -1;
}
// Set the OCR for the given timer,
// set the toggle count,
// then turn on the interrupts
switch (_timer)
{
#if defined(OCR0A) && defined(TIMSK0) && defined(OCIE0A)
case 0:
OCR0A = ocr;
timer0_toggle_count = toggle_count;
bitWrite(TIMSK0, OCIE0A, 1);
break;
#endif
case 1:
#if defined(OCR1A) && defined(TIMSK1) && defined(OCIE1A)
OCR1A = ocr;
timer1_toggle_count = toggle_count;
bitWrite(TIMSK1, OCIE1A, 1);
#elif defined(OCR1A) && defined(TIMSK) && defined(OCIE1A)
// this combination is for at least the ATmega32
OCR1A = ocr;
timer1_toggle_count = toggle_count;
bitWrite(TIMSK, OCIE1A, 1);
#endif
break;
#if defined(OCR2A) && defined(TIMSK2) && defined(OCIE2A)
case 2:
OCR2A = ocr;
timer2_toggle_count = toggle_count;
bitWrite(TIMSK2, OCIE2A, 1);
break;
#endif
#if defined(OCR3A) && defined(TIMSK3) && defined(OCIE3A)
case 3:
OCR3A = ocr;
timer3_toggle_count = toggle_count;
bitWrite(TIMSK3, OCIE3A, 1);
break;
#endif
#if defined(OCR4A) && defined(TIMSK4) && defined(OCIE4A)
case 4:
OCR4A = ocr;
timer4_toggle_count = toggle_count;
bitWrite(TIMSK4, OCIE4A, 1);
break;
#endif
#if defined(OCR5A) && defined(TIMSK5) && defined(OCIE5A)
case 5:
OCR5A = ocr;
timer5_toggle_count = toggle_count;
bitWrite(TIMSK5, OCIE5A, 1);
break;
#endif
}
}
}
It realies in this other function:
static int8_t toneBegin(uint8_t _pin)
{
int8_t _timer = -1;
// if we're already using the pin, the timer should be configured.
for (int i = 0; i < AVAILABLE_TONE_PINS; i++) {
if (tone_pins[i] == _pin) {
return pgm_read_byte(tone_pin_to_timer_PGM + i);
}
}
// search for an unused timer.
for (int i = 0; i < AVAILABLE_TONE_PINS; i++) {
if (tone_pins[i] == 255) {
tone_pins[i] = _pin;
_timer = pgm_read_byte(tone_pin_to_timer_PGM + i);
break;
}
}
if (_timer != -1)
{
// Set timer specific stuff
// All timers in CTC mode
// 8 bit timers will require changing prescalar values,
// whereas 16 bit timers are set to either ck/1 or ck/64 prescalar
switch (_timer)
{
#if defined(TCCR0A) && defined(TCCR0B) && defined(WGM01)
case 0:
// 8 bit timer
TCCR0A = 0;
TCCR0B = 0;
bitWrite(TCCR0A, WGM01, 1);
bitWrite(TCCR0B, CS00, 1);
timer0_pin_port = portOutputRegister(digitalPinToPort(_pin));
timer0_pin_mask = digitalPinToBitMask(_pin);
break;
#endif
#if defined(TCCR1A) && defined(TCCR1B) && defined(WGM12)
case 1:
// 16 bit timer
TCCR1A = 0;
TCCR1B = 0;
bitWrite(TCCR1B, WGM12, 1);
bitWrite(TCCR1B, CS10, 1);
timer1_pin_port = portOutputRegister(digitalPinToPort(_pin));
timer1_pin_mask = digitalPinToBitMask(_pin);
break;
#endif
#if defined(TCCR2A) && defined(TCCR2B)
case 2:
// 8 bit timer
TCCR2A = 0;
TCCR2B = 0;
bitWrite(TCCR2A, WGM21, 1);
bitWrite(TCCR2B, CS20, 1);
timer2_pin_port = portOutputRegister(digitalPinToPort(_pin));
timer2_pin_mask = digitalPinToBitMask(_pin);
break;
#endif
#if defined(TCCR3A) && defined(TCCR3B) && defined(TIMSK3)
case 3:
// 16 bit timer
TCCR3A = 0;
TCCR3B = 0;
bitWrite(TCCR3B, WGM32, 1);
bitWrite(TCCR3B, CS30, 1);
timer3_pin_port = portOutputRegister(digitalPinToPort(_pin));
timer3_pin_mask = digitalPinToBitMask(_pin);
break;
#endif
#if defined(TCCR4A) && defined(TCCR4B) && defined(TIMSK4)
case 4:
// 16 bit timer
TCCR4A = 0;
TCCR4B = 0;
#if defined(WGM42)
bitWrite(TCCR4B, WGM42, 1);
#elif defined(CS43)
// TODO this may not be correct
// atmega32u4
bitWrite(TCCR4B, CS43, 1);
#endif
bitWrite(TCCR4B, CS40, 1);
timer4_pin_port = portOutputRegister(digitalPinToPort(_pin));
timer4_pin_mask = digitalPinToBitMask(_pin);
break;
#endif
#if defined(TCCR5A) && defined(TCCR5B) && defined(TIMSK5)
case 5:
// 16 bit timer
TCCR5A = 0;
TCCR5B = 0;
bitWrite(TCCR5B, WGM52, 1);
bitWrite(TCCR5B, CS50, 1);
timer5_pin_port = portOutputRegister(digitalPinToPort(_pin));
timer5_pin_mask = digitalPinToBitMask(_pin);
break;
#endif
}
}
return _timer;
}
Does anyone know what does is this function doing? How it works? I am trying to code something simmilar in a PIC Microcotroller