i use an Arduino Mega compatible board (SainSmart Mega 2560 R3 ATmega2560-16AU) which has a rtc module attached (v1.1 ds1307rtc) and working on it with the attached code. I have used the TimeAlarms library (downloaded it from http://www.pjrc.com/teensy/td_libs_TimeAlarms.html) to have an alarm every hour. The alarms should occur at different minutes every hour, but for testing i have set them all to the 12th minute. This code is waiting for a correct time, which i can set via usb, serial interface. The code is working fine most of the times. But sometimes the alarm is not activated and my leds are not flashing. I don't know why and when this happens, i didn't any changes between the working flashing and not working. Also i can't see any hours where it doesn't working correct, afaik it works correct, but fails sometimes. If it failes, it looks like all hours after the failing hour are also failing and no alarm is triggered. I know about the restriction of 6 alarms in TimeAlarms.h and set the variable dtNBR_ALARMS in this file to 25.
As you can see i have implemented a printTime function which print out the rtc and the system time and always both are correct.
Has anyone an idea what i am doing wrong or why it fails sometimes?