Re: 405LP RTC reset

[Hollis Blanchard <hollis@austin.ibm.com>]

On Tue, 2002-12-17 at 18:55, David Gibson wrote:
>
> On Tue, Dec 17, 2002 at 12:43:32PM -0600, Hollis Blanchard wrote:
> > Here's the updated 405LP RTC reset diff (after David's move of the RTC
> > functions to ibm405lp.c). This patch
> > a) does a full RTC reset as specified in the docs
> > b) sets the RTC clock speed in RTC "Register A" DV bits, i.e. it does
> > not assume the firmware has done this correctly.
>
> One query though (I didn't think of this earlier) - is it such a great
> idea to go setting the reference clock frequency?  Unlike most other
> drivers, we can't just take over the RTC and do what we like with it
> once the kernel boots, because it has to keep running at the same rate
> even when the device is rebooting or (mostly) off.

The only issue I can think of here is the firmware setting it
incorrectly or not at all. In that case, a few seconds will be expanded
or compressed, but that's better than time running too fast or slow
forever, right?

Of course the rate settings must be battery-backed along with the time,
so you only need to set it once per RTC power loss. That includes
rebooting time and power off time.

-Hollis
--
PowerPC Linux
IBM Linux Technology Center

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/