IDT PCI Express 89HPES32NT24xG2, User Manual, Page: 40 / 744

IDT PES32NT24xG2 Device Overview
PES32NT24xG2 User Manual 1 - 4 January 30, 2013
Notes
PES32NT24xG2 ports support the following port operating modes.
– Disabled
– Unattached
– Upstream switch port (i.e., upstream PCI-to-PCI bridge)
– Downstream switch port (i.e., downstream PCI-to-PCI bridge)
– Upstream switch port with DMA function
– Upstream switch port with NT function
– Upstream switch port with NT and DMA functions
– NT function
– NT with DMA function
Figure 1.2 shows a logical diagram of a port. Depending on the port operating mode, the port may
contain one, two, or up to three PCI Express functions (e.g., PCI-to-PCI bridge, NT, and DMA functions).
The figure shows a port with all three functions. Multi-function ports always face upstream (i.e., they are
considered upstream ports).
– For example, a port in upstream switch port mode contains only an upstream PCI-to-PCI bridge
function. Similarly, a port in downstream switch port mode contains only a downstream PCI-to-PCI
bridge function. The PCI-to-PCI bridge function serves as a bridge between the PCI Express link
and the switch’s virtual PCI bus.
– A port in NT function mode contains a single Non Transparent (NT) endpoint function facing
upstream. This function serves as a non-transparent bridge between the port’s PCI Express link
and the switch’s NT Interconnect. Refer to section Non-Transparent Operation on page 1-8 for
details.
– A port in upstream switch port with NT and DMA functions mode contains three functions, an
upstream PCI-to-PCI bridge function, an NT function, and a DMA function. The port faces
upstream.
– A port in Disabled mode is disabled and it’s PCI Express link is turned off.
Other modes are possible, as listed above. Refer to Chapter 5 for details.
When a port is configured with two or more functions, data transfers across the functions (i.e., inter-func-
tion transfers) are possible. For example, TLPs may be transferred from the PCI-to-PCI bridge function to
the NT function and vice-versa. Similarly, TLPs may be transferred from the DMA function to the NT func-
tion and vice-versa. Finally, TLPs may be transferred from the DMA function to the PCI-to-PCI bridge func-
tion and vice-versa. Inter-function transfers occur within the port and are not emitted on the port’s PCI
Express link.
Note that a port’s link width is not determined by the port’s operating mode. Instead, the port’s maximum
link width is determined by the configuration of the stack associated with the port (e.g., a stack may be
configured as one x8 port or eight x1 ports). The actual link width that the port achieves is determined
during link training. Refer to Chapter 7, Link Operation, for details on link operation.