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millis()

[Time]

Description

Returns the number of milliseconds passed since the Arduino board began running the current program. This number will overflow (go back to zero), after approximately 50 days.

Syntax

time = millis()

Parameters

None

Returns

Number of milliseconds passed since the program started. Data type: unsigned long.

Example Code

This example code prints on the serial port the number of milliseconds passed since the Arduino board started running the code itself.

unsigned long myTime;

void setup() {
  Serial.begin(9600);
}
void loop() {
  Serial.print("Time: ");
  myTime = millis();

  Serial.println(myTime); // prints time since program started
  delay(1000);          // wait a second so as not to send massive amounts of data
}

Notes and Warnings

  • The return value for millis() is of type unsigned long, logic errors may occur if a programmer tries to do arithmetic with smaller data types such as int. Even signed long may encounter errors as its maximum value is half that of its unsigned counterpart.

  • millis() is incremented (for 16 MHz AVR chips and some others) every 1.024 milliseconds, then incrementing by 2 (rather than 1) every 41 or 42 ticks, to pull it back into synch; thus some millis() values are skipped. For accurate timing over short intervals, consider using micros().

  • millis() will wrap around to 0 after about 49 days (micros in about 71 minutes).

  • Reconfiguration of the microcontroller’s timers may result in inaccurate millis() readings. The "Arduino AVR Boards" and "Arduino megaAVR Boards" cores use Timer0 to generate millis(). The "Arduino ARM (32-bits) Boards" and "Arduino SAMD (32-bits ARM Cortex-M0+) Boards" cores use the SysTick timer.

See also