Drivers: PCI, ACPI, APIC

Driver code lives in src/drivers/. There is no unified driver model: each driver self-scans PCI by class or vendor/device and claims its BARs at fixed init call sites in kmain and the deferred boot task.

PCI

src/drivers/bus/pci/pci.cpp supports both config mechanisms:

• ECAM (MMIO) parsed from the ACPI MCFG table — primary path, full 4 KiB per function, up to 4 segments cached.
• Mechanism #1 I/O ports 0xCF8/0xCFC — fallback, first 256 bytes only.

Discovery scans bus 0-255, device 0-31, function 0-7 (multi-function only when the header type says so). Helpers exist for xHCI, AC97, HDA (vendor-restricted), and display devices.

BAR handling detects I/O vs memory, 32/64-bit, probes sizes with the write-all-ones/read-back method, and enables bus mastering / memory / I/O space per device.

MSI/MSI-X (msi.cpp): capability walk with a hop limit, MSI-X table mapping with up to 32 vectors, message address 0xFEE00000 | dest << 12, fixed edge delivery. Requires the APIC.

ACPI

src/drivers/acpi/acpi.cpp:

• RSDP from BootInfo->rsdp_address, with the legacy EBDA / 0xE0000-0x100000 scan as fallback.
• XSDT when revision >= 2 and present, else RSDT; per-table checksums.
• FADT: PM1a/PM1b control blocks, SMI command, ACPI enable value, reset register/value. The DSDT is scanned for the _S5_ package to obtain SLP_TYP values.
• MADT: consumed by the APIC layer and SMP bring-up.
• MCFG: consumed by PCI for ECAM.
• No HPET support.

Poweroff enables ACPI if needed, writes SLP_TYP | SLP_EN to the PM1 control blocks, brute-forces common SLP_TYP values, then falls back to VM ports (QEMU 0x604, Bochs 0xB004, VBox 0x4004). Reboot writes the FADT reset value to the reset register (I/O or MMIO).

APIC

• MADT parse: up to 8 IOAPICs (MMIO-mapped, all redirection entries masked at init) and up to 16 interrupt source overrides (bus 0, polarity/trigger decoded).
• LAPIC: base from the MADT header (with address-override record), default 0xFEE00000. The 8259 PIC is remapped and fully masked; spurious vector 0xFF.
• Routing: ISA IRQs map to vectors 32 + irq with ISO remapping; the IOAPIC covering the target GSI gets a fixed-delivery physical entry with the ISO's polarity and trigger bits.
• Vector space: 0-31 exceptions, 32 timer, 33 keyboard, 44 mouse, 0x80 syscall gate, dynamic allocations from 48-254 (xHCI MSI-X, TLB shootdown, RESCHED IPI, STOP IPI, MSI), 0xFF spurious.
• The interrupt dispatcher handles the timer (tick + possible reschedule), RESCHED (schedule), STOP (halt), PS/2 keyboard/mouse, and registered vector handlers; EOI via LAPIC.

Interrupts vs Polling

The kernel idle loop pumps input and network polling; device drivers that poll are driven from those paths or from their consumers.