[time-nuts] Portable Time Standard

[Achim Gratz]

Joe Hobart writes:
> I can read and write the DS3231 registers with a Raspberry Pi.  Unfortunately,
> the RPi kernel sends time to the RTC every 11 1/2 minutes.  This time is usually
> moderately accurate, but I have measured errors of up to 0.264 second, which is
> unacceptable.

That's the "11 minute mode" if you want a search term.  To get rid of it
you'd need to compile your own kernel (it's a compile-time option withz
no run-time parameters).  Only the first RTC found by the kernel should
be affected, although I haven't yet confirmed this myself.  I also don't
know if the rasPi kernel uses the symlink from /dev/rtc (in which case
you could perhaps simply point it to somewhere else) or if it picks the
first RTC device that has the hctosys property set.  This does not
happen if the SYNC flag in the kernel timekeeping code is not set (but
NTP will do that).  Last but not least, if you don't use (or blacklist)
the RTC driver and instead read the chip as a simple I²C device the
kernel will also leave it alone.


Regards,
Achim.
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