PCI Enumeration

This document describes the PCI bus enumeration implementation in the Kyronix kernel. It is the child of Driver Implementation Notes.

The Kyronix kernel enumerates the PCI bus using Port I/O-based configuration space access to discover and catalog all connected hardware devices.

Configuration Space Access

PCI configuration space is accessed through two standard I/O ports:

• 0xCF8 (Address register): Receives the configuration address, which encodes the bus number, device number, function number, and register offset.
• 0xCFC (Data register): Provides read/write access to the configuration data at the specified address.

Enumeration Procedure

1. Iterate over all 256 buses.
2. For each bus, iterate over all 32 devices.
3. For each device, iterate over all 8 functions.
4. Read the Vendor ID register at offset 0x00.
5. If the Vendor ID returns 0xFFFF, the device or function is absent; skip to the next function.
6. Read the Class Code, Subclass, Programming Interface (prog_if), Base Address Register (BAR) registers, and Header Type from the configuration space.
7. Store the device information in the global device table.

Usage

The global device table populated by PCI enumeration is consumed by the following drivers to discover and initialize their respective hardware:

• AHCI (Advanced Host Controller Interface) driver
• VirtIO driver
• Other PCI device drivers that query the device table during their probe sequences

Last reviewed: 2026-07-22