Abstract
The millis() returns the number of milliseconds since the board has booted.
ソースコード
Source Code
The millis() is defined in hardware/arduino/avr/cores/arduino/wiring.c as below. Only the souce code for Arduino UNO is quoted. The original source code supports many tips using #if’s.
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The millis() has no input argument and returns unsigned long value.
First it reserves the status register SREG.
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The SREG is a status register of ATMega328P.
Next it disables interrupt, copies the timer0_millis which holds the number of milliseconds to m, restores the reserved status register value and returns m. The timer0_millis is set in a interrupt handler named TIMER0_OVF_vect.
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cli() is a macro that executes an assembler macro to disable interrupt.
As SREG includes interrupt flag, it is not need to enable interrupt explicitly.
Version
Arduino 1.8.13
Last Update
January 23, 2021