Re: spitz: Real time clock?

[Richard Purdie <rpurdie@rpsys.net>]

On Fri, 2005-12-09 at 19:19 -0500, Nicolas Pitre wrote:
> The RTC count is lost on a hard reset.  It survives sleep mode though.
> 
> The fact is that PocketPC/WinCE is not meant to be "rebooted" and the 
> RTC on the PXA was probably designed with that fact.  The normal usage 
> pattern is to go into sleep mode all the time.

Which is the aim of the Zaurus kernel although it doesn't help when
developing...

> > could we do something like storing time on system shutdown and 
> > restoring it on bootup? That way at least time will be monotonic... 
> > Ok, that's userland problem.
> 
> I'd say so.

OpenZaurus/OE did have code to try and do this built into its images.
I'm not sure what its status is at the moment.

> > Is there way to reboot without "really" rebooting? That would help at
> > least in my usage case.
> 
> You should be able to "soft" reboot which will also preserve the RTC 
> count.

Based on past performance, the bootloader (in ROM) will probably
corrupt/reset the RTC but I'd like to be proved wrong.

Russell posted some rough code to linux-arm-kernel recently that allowed
you load a new kernel in a kexec sort of manner and that is probably the
best bet to preserve the RTC. This functionality would be useful on the
Zaurus in general.

Richard