PCI Device Characteristics
When the system boots, the firmware or operating system enumerates the PCI bus and assigns memory and I/O addresses to each device according to their requirements, then assigns interrupt numbers if required.
PCI devices are identified by two numbers: Vendor ID and Device ID. You need to know these numbers for your device before you start. The software uses these numbers to scan the PCI bus for the target device.
Each PCI device may be assigned up to six areas where their registers are mapped, and these areas may be in memory or I/O space, according to the device's requirements. You also need to know which of the six areas (BARs) are used by the device and the use of each.
A system may contain several devices of the same type. To locate a particular device, you must specify the instance in the wDeviceIndex field, where 0 (zero) represents the first instance, 1 the second, and so on.
PciFindDevice is the most common initial call. However, there are additional functions in the PCI library that return other characteristics and capabilities of the PCI devices, see the documentation.