Re: i386/RTC: old problem, new solution?
Richard Gooch (rgooch@atnf.csiro.au)
Thu, 20 May 1999 23:41:17 +1000
Riley Williams writes:
> Hi Ulrich.
>
> > maybe the problem running RTC in non-UTC time is known to you,
> > including its implications. Basically the kernel lacks two
> > things when booting:
>
> > 1) time zone
> > 2) Whether RTC runs UTC or local time
>
> Certainly on my setup, the kernel never even attempts to read the RTC
> itself and that's left to a userspace program (hwclock) that gets run
> from the boot scripts with the relevant parameters. The said program
> also makes use of a SymLink that tells it what the local timezone is,
> so has all the information needed to RE-initialise the system clock to
> match what the hardware clock claims is the case.
>
> > My solution would be:
>
> > 1) Add a kernel parameter like RTC=UTC|local
> > 2) Add a kernel parameter like TZ=+0200 (numeric notation used
> > in EMail)
>
> Both are already part of the hwclock program.
>
> > 3) Enhance routines that set the system time to update the RTC
> > as well
>
> Your wording is ambiguous, so I'll deal with both possible meanings:
>
> a. There are various programs available to synchronise the system
> clock with some external time standard. I use rdate as part of
> my dial up script, and a friend of mine uses a program that
> synchronises his system clock with that broadcast on teletext.
>
> b. The hwclock program also has the ability to set the RTC from
> the system clock.
>
> The combination of those two means that it is already possible to both
> synchronise the RTC with an external time standard and to ensure that
> the kernel is itself so synchronised.
>
> > I some people can convince me that it's a good idea, I might
> > develop a patch...
>
> Unfortunately, it's already been dealt with in userspace, so any
> kernel patch you developed would be unlikely to be applied anyway.
In fact, there already is a patch in the kernel:
CONFIG_APM_RTC_IS_GMT, but it's a temporary hack, until a better
scheme is implemented. The reason is that the kernel needs to know the
timezone the RTC is stored in when restoring the system clock after a
suspend/resume cycle. Automatically computing the difference has its
problems.
Regards,
Richard....
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