DFRobot FireBeetle ESP32-E Manual page 43

Software Serial
SoftwareSerial()
Running time Function
micros（）
Description: Returns the number of microseconds since the Arduino board began running the current program.
millis（）
Description: Returns the number of milliseconds passed since the Arduino board began running the current program.
Delay Functions
delay（ms）
Description: Pauses the program for the amount of time (in milliseconds) specified as parameter.
Parameter: ms: the number of milliseconds to pause. Allowed data types: unsigned long.
delayMicroseconds（us）
Description: Pauses the program for the amount of time (in microseconds) specified by the parameter. There are a thousand microseconds
in a millisecond and a million microseconds in a second.
Parameter: us: the number of microseconds to pause. Allowed data types: unsigned int.
8.3 Tone Functions
tone(pin, frequency, duration)
Description: Generates a square wave of the specified frequency (and 50% duty cycle) on a pin. A duration can be specified, otherwise the
wave continues until a call to noTone(). The pin can be connected to a piezo buzzer or other speaker to play tones.
Parameter:
pin：the Arduino pin on which to generate the tone.
frequency：the frequency of the tone in hertz. Allowed data types: unsigned int.