R

Chapter 14: Special Design Considerations

page 38). This instructs the attached PMA SERDES device to enter loopback mode as illustrated in Figure 14-1.

FPGA

Ethernet 1000BASE-X PCS/PMA or SGMII Core

TBI

1000BASE-X PMA

SERDES

Loopback occurs in external SERDES

Tx

Rx

Figure 14-1:Loopback Implementation Using the TBI

Core with RocketIO Transceiver

The loopback path is implemented in the core as illustrated in Figure 14-2. When placed into loopback, the data is routed from the transmitter path to the receiver path at the last possible point in the core. This point is immediately before the RocketIO interface. When placed in loopback, the core creates a constant stream of Idle code groups that are transmitted through the MGT or GTP transceiver in accordance with the IEEE 802.3 specification.

Earlier versions (before v5.0) of the core implemented loopback differently. The serial loopback feature of the RocketIO transceiver was used by driving the LOOPBACK[1:0] port of the RocketIO (MGT or GTP) transceiver. This is no longer the case, and the loopback[1:0] output port of the core is now permanently set to logic “00.” However, for debugging purposes, the LOOPBACK[1:0] input port of the RocketIO transceiver may be directly driven by the user logic to place it in either parallel or serial loopback mode.

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Ethernet 1000BASE-X PCS/PMA or SGMII v9.1

 

 

UG155 March 24, 2008

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Xilinx 1000BASE-X manual Core with RocketIO Transceiver, Special Design Considerations