Data Sheet

Datasheet, Volume 1 of 2 31
Interfaces
2.2.3 PCI Express* Configuration Mechanism
The PCI Express* (external graphics) link is mapped through a PCI-to-PCI bridge
structure.
PCI Express* extends the configuration space to 4096 bytes per-device/function, as
compared to 256 bytes allowed by the conventional PCI specification. PCI Express*
configuration space is divided into a PCI-compatible region (that consists of the first
256 bytes of a logical device's configuration space) and an extended PCI Express*
region (that consists of the remaining configuration space). The PCI-compatible region
can be accessed using either the mechanisms defined in the PCI specification or using
the enhanced PCI Express* configuration access mechanism described in the PCI
Express* Enhanced Configuration Mechanism section.
The PCI Express* Host Bridge is required to translate the memory-mapped PCI
Express* configuration space accesses from the host processor to PCI Express*
configuration cycles. To maintain compatibility with PCI configuration addressing
mechanisms, it is recommended that system software access the enhanced
configuration space using 32-bit operations (32-bit aligned) only. Refer the PCI Express
Base Specification for details of both the PCI-compatible and PCI Express* Enhanced
configuration mechanisms and transaction rules.
2.2.4 PCI Express* Equalization Methodology
Link equalization requires equalization for both TX and RX sides for the processor and
for the End point device.
Adjusting transmitter and receiver of the lanes is done to improve signal reception
quality and for improving link robustness and electrical margin.
The link timing margins and voltage margins are strongly dependent on equalization of
the link.
The processor supports the following:
• Full TX Equalization: Three Taps Linear Equalization (Pre, Current and Post
cursors), with FS/LF (Full Swing /Low Frequency) 24/8 values respectively.
Figure 2-3. PCI Express* Related Register Structures in the Processor