I've got a clock which uses an ATtiny84 to drive the display, and a RTC chip to keep time (it's battery-backup feature is the main reason for using a separate chip).
Is there a clever way to keep the AVR synced with the RTC?
I don't have enough pins on the ATtiny84 to use the square wave output from the RTC as an interrupt. The clock doesn't display seconds. So I just keep a timer which interrupts at 1 Hz (approximate because I'm using the internal oscillator). Whenever it reaches 30 seconds I pull the minutes and hours from the RTC, and resync the seconds. Does this sound like a reasonable method?