Advanced Configuration and Power Interface (ACPI)

This is implemented in acpi.

ACPI is a standard for operating systems to discover and configure computer hardware components, to perform power management, and to configure the system's power management features. It is a successor to Advanced Power Management (APM), and it is a part of the UEFI specification.

We have some support to some of the components of the ACPI standard.

ACPI comes in tables, and these tables include information about the system's hardware.

ACPI Tables Support

We have parsing support for these tables now, having support does mean we use all the features inside them. It just means that we can read the table, and that's it, some of them are used, but not all.

• RSDP: This is either provided by multiboot2 during boot, or we search for it in memory, and this just points to the RSDT or XSDT.
• RSDT: This is the Root System Description Table, and it contains pointers to other tables.
• MADT/APIC: This is the Multiple APIC Description Table, and it contains information about the APIC,see APIC for more details.
• FACP: This is the Fixed ACPI Description Table, and it contains information about the power management features of the system, also contain some info about the RTC.
• HPET: This is the High Precision Event Timer, and it contains information about the HPET, see HPET for more details.
• DSDT (not used*): This is the Differentiated System Description Table, and it contains AML code, which is used to configure the system.
• SSDT (not used*): This is the Secondary System Description Table, and it also contains AML code, which is used to configure the system.
• BGRT (not used): This is the Boot Graphics Resource Table, and it contains information about the boot logo, and it is used by the UEFI firmware.
• WAET (not used): This is the Windows ACPI Emulated Devices Table, and it contains information about the emulated devices, and it is used by the UEFI firmware.
• SRAT (not used): This is the System Resource Affinity Table, and it contains information about the system's memory and processors locality.

*: We don't use DSDT and SSDT data for now, but we do parse it as AML code, see AML for more details.

We use virtual space to map APIC tables, and then we copy them to the heap, this will make it easier to use, and we can reclaim ACPI memory later.

ACPI Control

During boot, we take control of ACPI registers, and also register an interrupt for ACPI events. (Implemented in acpi::setup_enable_acpi).

So, currently, we can get ACPI events, such as PowerButton pressed, and so on, but we need to implement shutdown behavior to correctly react to it and not just print it in the logs.