Thank you, I already readed this topic.
Now I try using Ubuntu 16.04 image and once I detect successfull my hwclock module (ds3231) at bus 1 by 0x68 address. But only once…
In my test i did not found module,but i had successful read amd wrote from/to it…but i used kernel 4.14 (official images using 4.4 where access to gpio is bit different).i don’t know if i2c is already enabled in 4.4 dts
I already find RTC support and ds1307 driver.
Now I successfull enable RTC support in BSP and enable rtc-ds1307 module driver.
Recompile and update kernel/u-boot.
And hardware clock is sucessfull work !!!
GPIO header I2C bus in BPI-R2 work at bus 1 !!!
i2cdetect not detect ds3231, but ds3231 work fine.
You see module dump by “i2c-dump 1 0x68 1” - 1st byte is seconds of current time.
CentOS and Ubuntu images not enabled RTC support by default - need download BSP and reconfigure kernel/u-boot and compile driver for RTC.