Xilinx 1000BASE-X - Manual (Page 95)

Ethernet 1000BASE-X PCS/PMA or SGMII v9.1 www.xilinx.com 95
UG155 March 24, 2008
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Chapter 8
SGMII / Dynamic Standards Switching
with RocketIO Transceivers
This chapter provides general guidelines for creating SGMII designs, and designs capable
of switching between 1000BASE-X and SGMII standards (Dynamic Standards Switching),
using a RocketIO transceiver. Throughout this chapter, any reference to SGMII also applies
to the Dynamic Standards Switching implementation.
The chapter begins with an explanation of the two Receiver Elastic Buffer
implementations: one implementation uses the buffer present in the RocketIO transceivers,
and the other uses a larger buffer, implemented in the FPGA fabric.
After selecting the Rx Elastic Buffer implementation type, an explanation of the RocketIO
transceiver and core logic in all supported device families is provided in the following
sections:
•
“RocketIO Logic using the RocketIO Rx Elastic Buffer,” page 98
•
“RocketIO Logic with the Fabric Rx Elastic Buffer,” page 98
Instances where multiple instantiations of the core are required when using the fabric
Receiver Elastic Buffer are then presented. Clock sharing should occur whenever possible
to save device resources.
Receiver Elastic Buffer Implementations
Selecting the Buffer Implementation from the GUI
The GUI provides two SGMII Capability options:
•
10/100/1000 Mbps (clock tolerance compliant with Ethernet specification)
•
10/100/1000 Mbps (restricted tolerance for clocks) OR 100/1000 Mbps
The first option, 10/100/1000 Mbps (clock tolerance compliant with Ethernet
specification) is the default and provides the implementation using the Receiver Elastic
Buffer in FPGA fabric. This alternative Receiver Elastic Buffer uses a single block RAM to
create a buffer twice as large as the one present in the RocketIO transceiver, for this reason
consuming extra logic resources. However, this default mode is reliable for all
implementations using standard Ethernet frame sizes. Further consideration must be
made for jumbo frames.
The second option, 10/100/1000 Mbps (restricted tolerance for clocks) or 100/1000 Mbps,
uses the receiver elastic buffer present in the RocketIOs. This is half the size and can
potentially underflow or overflow during SGMII frame reception at 10 Mbps operation