I have a functioning a DS3231 real time clock module on my Pi 3. The test I used to confirm operation is by obtaining output from the command hwclock -r. What causes me to wonder is, I didn’t install python-smbus or i2c-tools software or initial the I2C bus through raspi-config yet it appears I have a fully functioning RTC.
This would lead me to speculate the software and configuration is to enable user support for I2C and not for the device. User support meaning user interaction with the device. It appears at the system level communication with the RTC is possible once the dtoverlay is initialized in the config.txt file.
I found some documentation that describes how to obtain the temperature data that is available from the RTC module. Without the software installs and I2C configuration enabled this doesn’t appear to be possible. I reviewed the DS3231 spec sheet and I2C infrastructure is the communication backbone for the device. It appears to be supported for the device independent of what I do, once the dtoverlay is established.
This question is a lot more deeper dive than I normally do. Most times when things work I don't ask the question why. Now that I am retired, I guess I have more time on my hands. Can I assume the software and raspi-config interface configuration for I2C is for device interaction outside of the what the system can perform once the device tree overlay is established?
Sean