Altera PCI Compiler - Manual (Page 82)

3–8 User Guide Version 11.1 Altera Corporation
PCI Compiler October 2011
Functional Overview
The pci_mt64 and pci_t64 functions accept either 32-bit transactions
or 64-bit transactions on the PCI side. In both cases, the functions behave
as 64-bit agents on the local side. A 64-bit transaction differs from a 32-bit
transaction as follows:
■ In addition to asserting the framen signal, the PCI master asserts the
req64n
signal during the address phase informing the target device
that it is requesting a 64-bit transaction.
■ When the target device accepts the 64-bit transaction, it asserts
ack64n
in addition to devseln to inform the master device that it
is accepting the 64-bit transaction.
■ In a 64-bit transaction, the req64n signal behaves the same as the
framen
signal, and the ack64n signal behaves the same as
devseln . During data phases, data is driven over the ad[63..0]
bus and byte enables are driven over the cben[7..0] bus.
Additionally, parity for ad[63..32] and cben[7..4] is presented
over the par64n signal.
The pci_mt64, pci_t64, pci_mt32, and pci_t32 functions support
unlimited burst access cycles. Therefore, they can achieve a throughput
of up to 132 Megabytes per second (MByte/s) for 32-bit, 33-MHz
transactions, and up to 528 MByte/s for 64-bit, 66-MHz transactions.
However, the PCI Local Bus Specification, Revision 3.0 does not recommend
bursting beyond 16 data cycles because of the latency of other devices that
share the bus. You should be aware of the trade-off between bandwidth
and increased latency.