Chronodot on RPI

[Luiz Otavio O Souza]

On 17 April 2015 at 04:20, Milan Obuch wrote:

> Hello,
>
> I just received my DS3231 test board, rebuild kernel and activated
> appropriate DTB in boot. After first restart I've got
>
> # dmesg | grep ds3
> ds32310: <Maxim DS3231 RTC> at addr 0xd0 on iicbus1
> ds32310: oscillator has stopped, check the battery.
> ds32310: registered as a time-of-day clock (resolution 1000000us, adjustment 0.500000000s)
>
> Next restart, just
>
> # dmesg | grep ds3
> ds32310: <Maxim DS3231 RTC> at addr 0xd0 on iicbus1
> ds32310: registered as a time-of-day clock (resolution 1000000us, adjustment 0.500000000s)
>
> and
>
> sysctl dev.ds3231
> dev.ds3231.0.32khz_enable: 1
> dev.ds3231.0.sqw_mode: interrupt
> dev.ds3231.0.sqw_freq: 8192
> dev.ds3231.0.bbsqw: 0
> dev.ds3231.0.temp_conv: 0
> dev.ds3231.0.temperature: 30.7C
> dev.ds3231.0.%parent: iicbus1
> dev.ds3231.0.%pnpinfo: name=rtc compat=maxim,ds3231
> dev.ds3231.0.%location: addr=0xd0
> dev.ds3231.0.%driver: ds3231
> dev.ds3231.0.%desc: Maxim DS3231 RTC
> dev.ds3231.%parent:
>
> Basically, it seems just working. What else could I do to confirm that?
> Why the 'oscillator has stopped, check the battery' on first boot after
> installing? I think I swa it somewhere it's normal and will not occur
> anymore (maybe unless battery is fully discharged) but I am asking
> anyway...
>
> Regards,
> Milan

Yes, that's okay, the battery warning can happen because of (from
DS3231 datasheet):

1)  The first time power is applied.
2)  The voltages present on both VCC and VBAT are insufficient to
support oscillation.
3)  The EOSC bit is turned off in battery-backed mode.
4)  External influences on the crystal (i.e., noise, leakage, etc.).

To confirm it is working, set the system date, shutdown the RPi and
let it off for some period. Turn it on again (without ntpd) and check
the system date.

If you enable the ntpd together with RTC your system will crash, it is
a known issue (now...), the workaround is:

sysctl machdep.rtc_save_period=0

Luiz