ilyas:
My application board has to be as small as possible... thats why i want to eliminate external oscillators...i will try to change those clock parameters and then check.........
Surface-mount crystal glued to the top of the chip?
You can fiddle with the OSCCAL register but the internal oscillator isn't really designed for accurate real-word timing.
ilyas:
i heard that watchdog timers are very accurate... Is it possible to make millis work with watchdog timer..
i have no idea how to do this.....
Where did you hear that?
I really doubt it's any more accurate.
You can set up your own interrupt routine to increment a counter, yes.