I have an AM4 motherboard (Asrock Steel Legend B550M) with a M.2 E-Key socket. I rely on wired ethernet so such slot is left unused.
Out of curiosity I started looking up the specifics of E-Key and it appears that the interfaces are quite varied and interesting.
Apart from 2x PCIe lanes and USB 2.0, there is SDIO, I2S, UART, I2C and a handful of control signals.
From what I understand the I2C bus, on an ATX motherboard, is where all the control and reporting exchanges between the devices happen: temperature reporting, voltage and current sensing, fans and LED control, managing of the VRM, etc.
Since there are no standards or conventions shared between MB manufacturers it’s very tricky to identify which IC performs each function and the format used.
First of all, should I expect to be just one bus or multiple ‘trunks’, electrically and logically separated?
Second, any clue on which devices would be on the “M.2 I2C” bus trunk?
Third, is anyone aware of any product/project using this interface to tap into the HW layer of a PC motherboard?