Which intel tech document for IOC and SOC communication in boot up?

hi,

We worked on MRB intel reference board, which has Apollo lake SOC mounted, and another IOC module.

We understand during boot up phase, IOC will send some commands to the bootloader, which is running in SOC side, in order to boot the system(e.g.: linux).

Can you help me to know which intel tech document (document number?)  is preferred to be referred in order to understand how IOC to control SOC boot up via some commands?

Thanks.