Altera PCI Compiler - Manual (Page 168)

3–94 User Guide Version 11.1 Altera Corporation
PCI Compiler October 2011
Master Mode Operation
4. A turn-around cycle on the ad bus occurs during the clock cycle
immediately following the address phase. During the turn-around
cycle, the PCI side tri-states the ad bus, but drives the correct byte
enables on the cben bus for the first data phase. This process is
necessary because the pci_mt64 function must release the bus so
another PCI agent can drive it.
5. A PCI target asserts devseln to claim the transaction. One or more
data phases follow, depending on the type of read transaction.
The pci_mt64 and pci_mt32 functions treat memory read, memory
read multiple, and memory read line commands in the same way. Any
additional requirements for the memory read multiple and memory read
line commands must be implemented by the local-side application.