At 03:33 PM 10/28/2009, J. Mike Needham wrote...
Eventually I want to package these for marketing, so they will become
more
specialized once we get a prototype built
You didn't say what level of accuracy you want, but from your
description ("bedside alarm clock"), 1 second accuracy is way more than
sufficient (I've not seen an alarm clock with a seconds display, but
then again, this is the time-nuts list).
If you use Linux, as you mentioned, the kernel RTC should be
sufficient. You just need to drive a display.
Consider just doing an "ntpdate" as an update mechanism, rather than
the full ntp steering code. Even with that, you shouldn't be out by
more than a second even if you only poll every few hours (e.g. 1 second
drift per 6 hours is a cheap 50 ppm crystal driving the processor).
I'd think that for low-cost volume, you'd just use the chosen processor
to keep track of time, and output to a display. Most of the time, a
clock as you described has nothing to do, but count time. So, do that
by counting cycles in an update loop. Whatever error accumulates when a
user is making settings will be corrected by NTP at the next update.
You'd avoid the cost of resources to support even embedded Linux, and
only have to get network and ntpdate code ported.
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