SMBUS and I2C are closely related buses. The SPD (Serial Presence Detect) of the DIMM's are I2C devices that need to be read during Developer Manual/RAM init.
For characterizing I2C on a unsupported motherboard I used the following tools:
- sensors-detect (lm-sensors)
Using this tools on a normal bios on the motherboard its easy to identify the appropriate address for the SPD data.