[Letux-kernel] Where does RTC actually work

Andreas Kemnade andreas at kemnade.info
Wed Feb 1 18:32:49 CET 2017


On Wed, 1 Feb 2017 17:59:12 +0100
"H. Nikolaus Schaller" <hns at goldelico.com> wrote:
[...]
> 
> So unless either this pinmux setting is not executed by u-boot
> although it is in the code or some other component overwrites (maybe
> not even intends to) the pinmux it should remain "1" all the time. So
> the clock should always be writeable.
> 
you are mixing things up!

The problem is not that the clock is not
writable. It is written accidently somewhere (probably new spl/uboot).
I checked I2c registers: 
It is set correctly by hwclock --systohc
The *hour* (and *only* that, not the year) becomes wrong after power
down (aka
10 seconds button press) at the next get time request.

I read it out in uboot cmdline. (see my other mails to that topic).
booting the 4.7.0 kernel gives at some point after module loading the
wrong year. Probably (have not checked yet) reset because of the wrong
hour like
if (rtc_hour > 23) 
   reset_rtc();

> > - something mixes up i2c registers and
> >   - messes with the clock and/or
> >   - some oscillators
> 
> Well, it might be something with the supercap, but I had measured the
> voltage and it goes up to 3.2V during operation and it takes ca. 45
> seconds after powering down and removing the battery to make it go
> down to 3.0V.
> 
That would not explain problems without battery removal.

Regards,
Andreas
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