Parsing ACPI information

ACPI Specification

ACPI is a standard for controlling things like power and temperatures in computers. It's also useful for getting some information about the machine, such as number of processors - which is what Mittos will be using it for (at least at first).

The bootloader will find the Root System Descriptor Pointer and provide it in a boot tag. Then the data just needs to be parsed.

The RSDP contains a pointer to the Root System Descriptor Table which contains pointers to more System Descriptor Tables.

The important fields for parsing a System Descript Tables are as follows:

struct sdt {
    char signature[4];
    uint32_t length;
    uint8_t _[28];
    uint32_t data[];
}__attribute__((packed));

So I step through the pointers in the RSDT data field until I find an SDT with signature "APIC". That should contain the Multiple APIC Description Table.

The MADT in turn contains a number of fields with information - among other things - about Processor Local APICs, I/O Apics and IRQ redirections. Those are things I may be interested in, and therefore store in some global data structures.

Relevant files

src/kernel/cpu/acpi.c

1.2 KiB Raw Blame History

Parsing ACPI information

Relevant files

1.2 KiB

Raw Blame History