# Bridge Header Offsets Constants that specify offsets to distinct registers in a memory range. ## Topics ### Offsets [`kPCI2PCIOffsetPrimaryBus`](/documentation/PCIDriverKit/kPCI2PCIOffsetPrimaryBus) The offset to the primary bus number register. [`kPCI2PCIOffsetSecondaryBus`](/documentation/PCIDriverKit/kPCI2PCIOffsetSecondaryBus) The offset to the secondary bus number register. [`kPCI2PCIOffsetSubordinateBus`](/documentation/PCIDriverKit/kPCI2PCIOffsetSubordinateBus) The offset to the subordinate bus number register. [`kPCI2PCIOffsetSecondaryLT`](/documentation/PCIDriverKit/kPCI2PCIOffsetSecondaryLT) The offset to the secondary latency timer register. [`kPCI2PCIOffsetIORange`](/documentation/PCIDriverKit/kPCI2PCIOffsetIORange) The offset to the I/O base upper and I/O limit upper registers. [`kPCI2PCIOffsetMemoryRange`](/documentation/PCIDriverKit/kPCI2PCIOffsetMemoryRange) The offset to the memory base and memory limit registers. [`kPCI2PCIOffsetPrefetchMemoryRange`](/documentation/PCIDriverKit/kPCI2PCIOffsetPrefetchMemoryRange) The offset to the prefetchable memory base and prefetchable memory limit registers. [`kPCI2PCIOffsetPrefetchUpperBase`](/documentation/PCIDriverKit/kPCI2PCIOffsetPrefetchUpperBase) The offset to the prefetchable base upper 32 bits register. [`kPCI2PCIOffsetPrefetchUpperLimit`](/documentation/PCIDriverKit/kPCI2PCIOffsetPrefetchUpperLimit) The offset to the prefetchable limit upper 32 bits registers. [`kPCI2PCIOffsetUpperIORange`](/documentation/PCIDriverKit/kPCI2PCIOffsetUpperIORange) The offset to the I/O base upper and I/O limit upper registers. [`kPCI2PCIOffsetBridgeControl`](/documentation/PCIDriverKit/kPCI2PCIOffsetBridgeControl) The offset to the bridge control register. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)