求大佬帮忙分析一下这段代码

int speakerPin = 9;
int controlPin = 0;
void setup() {
pinMode(speakerPin, OUTPUT);
}
/*
play a tone with period given in microseconds for a duration
given in milliseconds
*/
void playTone(int period, int duration) {
// elapsed time in microseconds, the long is needed to get
// a big enough range.
long elapsedTime = 0;
// note we are making a slight error here if period is not even
int halfPeriod = period / 2;
while (elapsedTime < duration * 1000L) {
// generate a square wave of the given period. Half the
// period is on, the other half is off.
digitalWrite(speakerPin, HIGH);
delayMicroseconds(halfPeriod);
digitalWrite(speakerPin, LOW);
delayMicroseconds(halfPeriod);
// count the time we just consumed for one cycle of the tone
elapsedTime = elapsedTime + period;
}
}
void loop() {
int period;
period = analogRead(controlPin);
playTone(period, 500);
}