Here's my situation:
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I'm running an arduino pro mini on batteries.
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The arduino will be woken up by an external interrupt on INT0 on fairly regular intervals (roughly every 2 seconds, varies at different times of day). Otherwise it will be sleeping in the as deep a sleep as possible to preserve power (it will also be slightly modded to remove other power hogs like the regulator and power LED).
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At every interrupt, the processor should save the time that interrupt arrived with about +- 1s accuracy.
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Data will be sent to a server about once a day at which point the arduino can sync up its timekeeping to prevent drift.
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Contacting the server consumes a lot of power, so it should not be done except when sending collected data.
Now, my question is this: Is it possible for the arduino to sleep while still keeping some internal timer running that will keep fairly accurate time up to 24 hours? Or do i have to run with an external RTC IC?
Thanks in advance for any suggestions!