PCI

This document describes the PCI bus enumeration in the Kyronix kernel. It is the child of Drivers.

Source

kernel/drivers/pci.c

Overview

PCI (Peripheral Component Interconnect) enumeration discovers and configures all PCI devices on the bus. The kernel scans the standard I/O configuration space to identify devices.

Configuration Space Access

PCI configuration is accessed via I/O ports:

Device Structure

struct pci_device {
    uint8_t  bus, dev, func;
    uint16_t vendor_id, device_id;
    uint8_t  class, subclass;
    uint8_t  prog_if;
    uint8_t  header_type;
    uint32_t bar[6];
    uint16_t command;
};

Enumeration

pci_enumerate() scans all 256 buses, 32 devices, and 8 functions:

1. For each device/function, read vendor ID
2. If vendor ID is 0xFFFF, device does not exist – skip
3. Read class, subclass, BAR registers, and header type
4. Store in global device table

BAR (Base Address Register) Types

BARs are used by drivers (AHCI, VirtIO) to access device registers.

Last reviewed: 2026-07-22