
45732 AMD 780E Databook 3.10
© 2009 Advanced Micro Devices, Inc.
2-2
Proprietary
Host Interface
HyperTransport I/O Link Specification
from the HyperTransport Consortium.
Figure 2-2, “Host Interface Block
Diagram,”
illustrates the basic blocks of the host bus interface of the RS780E.
Figure 2-2 Host Interface Block Diagram
The HyperTransport (HT) Interface, formerly known as the LDT (Lightning Data Transport) interface, is a high speed,
packet-based link implemented on two unidirectional buses. It is a point-to-point interface where data can flow both
upstream and downstream at the same time. The commands, addresses, and data travel in packets on the HyperTransport
link. Lengths of packets are in multiples of four bytes. The HT link consists of three parts: the physical layer (PHY), the
data link layer, and the protocol/transaction layer. The PHY is the physical interface between the RS780E and the CPU.
The data link layer includes the initialization and configuration sequences, periodic redundancy checks,
connect/disconnect sequences, and information packet flow controls. The protocol layer is responsible for maintaining
strict ordering rules defined by the HT protocol.
The RS780E HyperTransport bus interface consists of eighteen unidirectional differential data/control pairs and two
differential clock pairs in each of the upstream and downstream direction. On power up, the HT link is 8-bit wide and runs
at a default speed of 400MT/s. After negotiation, carried out by the HW and SW together, the link width can be brought
up to 16-bit and the interface can run up to 4.4GT/s. The interface is illustrated in
Figure 2-3, “RS780E Host Bus
Interface Signals.”
The signal name and direction for each signal is shown with respect to the processor. Note that the
signal names may be different from those used in the pin listing of the RS780E. Detailed descriptions of the signals are
given in
section 3.3, “CPU HyperTransport™ Interface‚’ on page 3-5
.
HT Interface to CPU (PHY)
Configuration
Registers
Root Complex
Memory Controller
LTA
LRA
SCH
Data Link Layer
Protocol/Transaction Layer