This is a port of the Adafruit driver and DateTime library for the DS1307 RTC controller

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Import libraryAdafruit_RTCLib

This is a port of the Adafruit driver and DateTime library for the DS1307 RTC controller

This library was ported from Adafruit's RTCLib and then modified by splitting the out the driver separate from the DateTime class.

Also add support for access to the 56 bytes of user accessible battery backed ram.

I did not port, but left the RTC_Millis class in, and commented it out.

DS1307 RTC Breakout


 *  Copyright (c) 2012 Neal Horman -
 *  License: MIT open source (
 *      Summary;
 *      Use / modify / distribute / publish it how you want and 
 *      if you use it, or don't, you can't hold me liable for how
 *      it does or doesn't work.
 *      If it doesn't work how you want, don't use it, or change
 *      it so that it does work.

#include "mbed.h"
#include "DS1307.h"
class I2C2 : public I2C
    I2C2 ( PinName sda, PinName scl, int hz, const char *name = NULL) : I2C ( sda, scl, name) { frequency(hz * 100); };
I2C2 gI2c ( p28, p27, 100 );
RtcDs1307 gRtc ( gI2c );
Serial gSerial(USBTX, USBRX);
void printDT(char *pre, DateTime &dt)
    gSerial.printf("%s - %u/%u/%02u %2u:%02u:%02u\r\n"
bool rtcUpdate(RtcDs1307 &rtc, int32_t bias) // this must be signed
{   bool bUpdated = false;
    // Use the compiled date/time as a basis for setting the clock.
    // We assign it to a signed integer so that negative biases work correctly
    int64_t compiledTime = DateTime(__DATE__,__TIME__).unixtime();
    // This assumes that the program is run VERY soon after the initial compile.
    time_t localt = DateTime(compiledTime + bias).unixtime(); // offset by bias
    // If the stored static time stamp does not equal the compiled time stamp,
    // then we need to update the RTC clock and the stored time stamp
    if(*((time_t *)&rtc[0]) != localt)
        // Update the RTC time as local time, not GMT/UTC
        // Store the new compiled time statically in the object ram image
        *((time_t *)&rtc[0]) = localt;
        // Push the object ram image to the RTC ram image
        bUpdated = rtc.commit();
    return bUpdated;
int main()
{   time_t tick = 0;
    if(rtcUpdate(gRtc, -(5*60*60) )) // CDT
        gSerial.printf("Updated RTC to compiled time\r\n");
    gSerial.printf("compiled %s %s\r\n",__DATE__,__TIME__);
    DateTime timeFlashed(*((time_t *)&gRtc[0]));
    printDT("last flashed on",timeFlashed);
    DateTime dt =;
    gSerial.printf("rtc clock is %s\r\n", (gRtc.isRunning() ? "running" : "halted"));
        if(time(NULL) >= tick)
            dt =;
            gSerial.printf("%u/%u/%02u %2u:%02u:%02u          \r"
            tick = time(NULL)+1;

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Files at revision 1:2c4e81ecda67

Name Size Actions
DS1307.cpp 2288 Revisions Annotate
DS1307.h 750 Revisions Annotate
DateTime.cpp 3959 Revisions Annotate
DateTime.h 1399 Revisions Annotate