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AR# 29218

Virtex-5/Spartan-6 GTP/GTX RocketIO - Loss of Sync (LOS) does not behave as expected in certain conditions


The LOS state machine in GTP/GTX does not behave as specified in the various Ethernet protocols. This Answer Record describes the LOS state machine behavior and prescribes a method by which to work around this issue. The method might not be suitable for all designs, specifically ones that require Channel Bonding.


When Channel Bonding is not used

When Channel Bonding is not used, the Loss of Sync state machine inside the GTP/GTX will get stuck in the RESYNC state indefinitely.

To work around this issue in designs that do not use Channel Bonding, you can set:

CHAN_BOND_SEQ_1_1 to 10'b0100000000

The graphic below shows the same design with the above attribute changes.

This work-around will not adversely affect single-channel designs since 0x00 is not a valid K character and will not appear in any 8b/10b encoded data stream.

When Channel Bonding is used

When channel bonding is used in the design, you can expect the Loss of Sync state machine to report RESYNC when any K character is detected.

There is no method by which to work around this issue when Channel Bonding is enabled. The Xilinx XAUI Core bypasses this issue by implementing LOS in the FPGA fabric when the Implement IEEE Synchronization State Machine option is selected in the CORE Generator GUI. When this option is not selected, the XAUI Core only uses bit 1 of the RXLOSSOFSYNC port.
AR# 29218
Date 01/21/2013
Status Active
Type General Article
  • Spartan-6 LXT
  • Virtex-5 FXT
  • Virtex-5 LXT
  • More
  • Virtex-5 SXT
  • Virtex-5 TXT
  • Less