markjeronimus Posted September 13, 2017 Posted September 13, 2017 Are there any plans to add support for the MCP7940 real-time clock? It's much cheaper than the DS1307 and mostly compatible. The biggest difference is Reg0b7 which is "Clock-Halt" in the 1307 but "STart" in the 7940. The 7940 also has some extra register bits like OSCEN which are default 0 in the 1307. I tried naively enabling the rtc-ds1307 module and it didn't work. An actual DS1307 chip worked immediately (just hot-plugging the break-out boards while executing "hwclock -rf /dev/rtc1"). The actual error I get is: "Timed out while waiting for the time to change", "The Hardware Clock registers contain values that are either invalid (e.g. 50th day of the month) or beyond the range we can handle (e.g. Year 2095)". I tried setting the time to a known good value and got just "Timed out while waiting for the time to change".
martinayotte Posted September 13, 2017 Posted September 13, 2017 Linux Kernel doesn't seems to have any support for MCP7940 ... You can probably handle this chip with userspace program, such as small python script called from /etc/rc.local which can then set the system clock accordingly.
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