acpi - RSDP/FADT discovery, shutdown & reboot

Header: kernel/include/kernel/acpi.h Source: arch/i386/core/acpi.c

acpi_init() scans for the RSDP and parses the FADT / DSDT. It must run after paging is enabled (the ACPI tables in low physical memory are covered by the 256 MiB identity-mapped window). On success the PM1a/PM1b control-block ports and the S5 sleep-type values are cached for acpi_shutdown(). Returns 1 if tables were found and parsed, 0 otherwise.

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API

Function	Role
acpi_init()	Find + parse the tables; cache the PM1/S5 values. Returns 1 on success.
acpi_checksum(table,len)	Verify a table’s byte sum is zero (ACPI-valid). Backs the test_acpi_checksum ktest.
acpi_shutdown()	Power off via ACPI S5 (“soft off”). Never returns.
acpi_reboot()	Reset the machine. Never returns.

Fallback chains (resilient by design)

acpi_shutdown() tries, in order: (1) the ACPI PM1 control registers, (2) the QEMU/Bochs I/O-port fallbacks (0x604 / 0xB004), (3) a cli; hlt spin (last resort — the machine appears frozen).

acpi_reboot() tries: (1) the ACPI reset register (FADT rev ≥ 2, I/O-port variant), (2) the PS/2 keyboard-controller CPU-reset pulse (outb(0x64, 0xFE)), (3) a triple-fault (zero-limit IDT + int $0).

These back the shutdown/poweroff/halt and reboot shell commands and the GUI power menu. The same 8042-reset + triple-fault tail is reused inline by the hwspecs boot mode’s “press a key to reboot” and by the fail-safe panic path (debug).