Gigabit Transceivers

The SYZYGY Transceiver port offers two channels of high speed transceiver lanes connected to the Zynq 7000 GTP transceiver pins on the Brain-1.

IBERT Configuration

Xilinx provides the IBERT tool to test and experiment with gigabit transceivers.  The settings below are compatible with the SYZYGY Brain-1 using Vivado 2017.3:

Silicon Version 
ProtocolCustom 1
Line Rate3.75 Gbps
Data Width32
Ref Clk125.000 MHz
Quad Count1
GTP LocationQUAD_112
Protocol SelectedCustom 1 / 3.75 Gbps
Refclk SelectionMGTREFCLK0 112
TXUSRCLK SourceChannel 0
Clock TypeSystem Clock
SourceQUAD112 0
Frequency (MHz)125.0

Gigabit Transceiver IBERT Performance

Xilinx’s IBERT tool enables an automated self-measurement of a GTP channel’s eye diagram when used in a loopback mode. Eye diagrams for three different speeds were captured using this tool with a simple loopback peripheral attached to the expansion headers. While results may vary, these are typical captures and actually represent the worst case capture over all channels for the respective rates.

Note that in loopback modes, it can be helpful to disable the GBT DFE (decision feedback equalizer) to avoid over-compensation. In these test cases, the DFE has been left enabled.

Direct Transceiver Loopback

Loopback Through 6″ SYZYGY Cable

Loopback Through 3m SYZYGY Cable