All our PCI devices are 64-bit, do we need pull-ups on the secondary PCI expansion signals?
The secondary PCI bus may only have 64-bit devices connected to it, but you can’t prevent 32-bit transactions from happening. Configuration cycles, I/O cycles and non-prefetchable memory all use 32-bit transactions. The PCI v2.2 Spec states in section 3.8, “The bandwidth requirements for I/O and configuration commands cannot justify the added complexity and, therefore, only memory transactions support 64-bit data transfers.” Since 32-bit transactions cannot be avoided, we suggest using the pull-ups. For more information on the PCI Spec Version 2.2 please see PCISIG.
