Re: [iPAQ] real-time clock accuracy

On Mon, 11 Jun 2001, Jeff Sutherland wrote:

> On Mon, Jun 11, 2001 at 10:59:22AM -0400, Nicolas Pitre wrote:
> >
> >
> > On Mon, 11 Jun 2001, Russ Nelson wrote:
> >
> > > My ipaq has been up for fourteen days, and my hardware clock is now
> > > four hours ahead of the real time of day. Is there anything to be
> > > done about this?
> >
> > According to the SA1110 manual, there is a "trim" register that allows you
> > to adjust, or compensate, for unprecise cristal clocking the RTC. However
> > the correction is said to be at most +/-5 seconds per month.
> >
> >
> > Nicolas
>
> But if it's been up for 14 days, it's running off the 3.6864MHz crystal,
> no?

The software maintained clock which Linux uses is based on the 3.6864MHz
clock. The hardware RTC that survives through sleep mode is based on what
is assumed to be a 32.768KHz clock by default. The RTC has a register to
specify what is the real RTC clock frequency which lets you correct the
clock error with a precision of +/- 5 sec per month.

Nicolas
Received on Mon Jun 11 11:17:30 2001