BCM4354 Data Sheet
PCI Express Interface
Each layer is partitioned into dedicated transmit and receive units that allow point-to-point communication
between the host and BCM4354 device. The transmit side processes outbound packets whereas the receive
side processes inbound packets. Packets are formed and generated in the Transaction and Data Link Layer for
transmission onto the high-speed links and onto the receiving device. A header is added at the beginning to
indicate the packet type and any other optional fields.
Figure 29: PCI Express Layer Model
HW/SW Interface
HW/SW Interface
Transaction
Layer
Transaction
Layer
Data Link
Layer
Data Link
Layer
Physical Layer
Physical Layer
Logical Subblock
Logical Subblock
Electrical Subblock
Electrical Subblock
TX
RX
TX
RX
Transaction Layer Interface
The PCIe core employs a packet-based protocol to transfer data between the host and BCM4354 device,
delivering new levels of performance and features. The upper layer of the PCIe is the Transaction Layer. The
Transaction layer is primarily responsible for assembly and disassembly of Transaction Layer Packets (TLPs).
TLP structure contains header, data payload, and End-to-End CRC (ECRC) fields, which are used to
communicate transactions, such as read and write requests and other events.
A pipelined full split-transaction protocol is implemented in this layer to maximize efficient communication
between devices with credit-based flow control of TLP, which eliminates wasted link bandwidth due to retries.
Data Link Layer
The data link layer serves as an intermediate stage between the transaction layer and the physical layer. Its
primary responsibility is to provide reliable, efficient mechanism for the exchange of TLPs between two directly
connected components on the link. Services provided by the data link layer include data exchange, initialization,
error detection and correction, and retry services.
Data Link Layer Packets (DLLPs) are generated and consumed by the data link layer. DLLPs are the
mechanism used to transfer link management information between data link layers of the two directly connected
components on the link, including TLP acknowledgement, power management, and flow control.
Broadcom®
October 15, 2014 • 4354-DS109-R
Page 72
BROADCOM CONFIDENTIAL
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