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The RTC (Real-Time Clock) provides mechanisms to set the current time of the hardware RTC with set_time API. The time is set as an offset measured in seconds from the time epoch (Unix Epoch - January 1, 1970).

You can use the attach_rtc API to hook external RTC for using C time functions. It provides you with init(), read(), write() and isenabled() functions to be attached. Time provides more information about C date and time standard library functions.

RTC class APIs are thread safe.

RTC can keep track of time even in a powered down state if the secondary source of power (battery) is connected.

RTC function reference

RTC Time example

/* mbed Example Program
 * Copyright (c) 2006-2014 ARM Limited
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *     http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.
#include "mbed.h"

int main() {
    set_time(1256729737);  // Set RTC time to Wed, 28 Oct 2009 11:35:37

    while (true) {
        time_t seconds = time(NULL);
        printf("Time as seconds since January 1, 1970 = %u\n", (unsigned int)seconds);
        printf("Time as a basic string = %s", ctime(&seconds));

        char buffer[32];
        strftime(buffer, 32, "%I:%M %p\n", localtime(&seconds));
        printf("Time as a custom formatted string = %s", buffer);

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