We're not talking about embedded devices in a server thread :) I'm not sure what you're calling "an ACPI controller". (You seem to be thinking of MMUs and PICs

We're not talking about embedded devices in a server thread :) I'm not sure what you're calling "an ACPI controller". (You seem to be thinking of MMUs and PICs??) ACPI is a software interface. The tables are the ACPI. It's possible to implement ACPI on a system that originally shipped with U-Boot and Flattened Device Trees. Say, for the Raspberry Pi: https://github.com/tianocore/edk2-platforms/tree/8b72f720d53ee2df22e5d4e2479c6f0d0a870af0/Platform/RaspberryPi/RPi3/AcpiTables https://github.com/tianocore/edk2-platforms/tree/8b72f720d53...