Summary:
Existing code recognizes the mcp7941x RTC, but this RTC has an
enable bit at the same location as the "Clock Halt" bit on the ds1307, with an
opposite assertion (set == on, whereas CH set == clock stopped). Thus the
current code halts the clock, with no way to enable it.
Reviewed By: ian
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D12961
Don't enable the oscillator when it is found to be stopped at init time,
just let the first setting of valid time start it. But still report a dead
battery if it's stopped at init time.
Don't force the chip into 24hr mode, just cope with whatever mode it is
already in.
Align the RTC clock to top of second when setting it.
This is compatible with the ds1307, but comparing the mcp7941x datasheet vs the
ds1307 code, appears there is one bit placement difference, so that is now
accounted for.
Relnotes: yes
Many thanks to ian who gently provided me the DS1307 breakout board.
Tested on: Raspberry pi
Differential Revision: https://reviews.freebsd.org/D2022
Reviewed by: rpaulo
