Datasheet, Volume 1
19
Interfaces
The transmission side of the Data Link Layer accepts TLPs assembled by the
Transaction Layer, calculates and applies data protection code and TLP sequence
number, and submits them to Physical Layer for transmission across the Link. The
receiving Data Link Layer is responsible for checking the integrity of received TLPs and
for submitting them to the Transaction Layer for further processing. On detection of TLP
error(s), this layer is responsible for requesting retransmission of TLPs until information
is correctly received, or the Link is determined to have failed. The Data Link Layer also
generates and consumes packets which are used for Link management functions.
2.2.1.3
Physical Layer
The Physical Layer includes all circuitry for interface operation, including driver and
input buffers, parallel-to-serial and serial-to-parallel conversion, PLL(s), and impedance
matching circuitry. It also includes logical functions related to interface initialization and
maintenance. The Physical Layer exchanges data with the Data Link Layer in an
implementation-specific format, and is responsible for converting this to an appropriate
serialized format and transmitting it across the PCI Express Link at a frequency and
width compatible with the remote device.
2.2.2
PCI Express* Configuration Mechanism
The PCI Express 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 (which consists of the first
256 bytes of a logical device's configuration space) and an extended PCI Express region
(which 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.
See the
PCI Express* Base Specification
for details of both the PCI-compatible and PCI
Express Enhanced configuration mechanisms and transaction rules.
2.3
DMI2/PCI Express* Interface
Direct Media Interface 2 (DMI2) connects the processor to the Platform Controller Hub
(PCH). DMI2 is similar to a four-lane PCI Express supporting a speed of 5 GT/s per
lane. Refer to
Section 6.3, “DMI2 / PCI Express* Port 0 Signals”
for additional details.
Note:
Only DMI2 x4 configuration is supported.
2.3.1
DMI2 Error Flow
DMI2 can only generate SERR in response to errors; never SCI, SMI, MSI, PCI INT, or
GPE. Any DMI2 related SERR activity is associated with Device 0.
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