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AR# 30042

Virtex-5 GTP RocketIO - Clock correction does not occur in unbonded transceivers when CHAN_BOND_MODE = "SLAVE"


The GTP attribute CHAN_BOND_MODE controls the Channel Bonding logic in the GTP's Elastic Buffer. When this attribute is set to "SLAVE", the logic that controls the Elastic Buffer must follow the rules of a Channel Bonded slave. This includes rules governing Clock Correction. A Channel Bonded Slave transceiver is not allowed to Clock Correct without permission from the Master. As a result, if a GTP's CHAN_BOND_MODE = "SLAVE" and it is not bonded to a Master, it will ignore Clock Correction sequences. This typically results in an RX Buffer overflow or underflow.


This behavior is common when implementing designs that can "down-train" the number of transceivers in a link, such as in Serial RapidIO. If a link down-trains from multiple transceivers to a single transceiver, you can ensure that the single transceiver's CHAN_BOND_MODE attribute is not set to "SLAVE" as follows:
- Ensure that the link down-trains in such a way that the last lane operating is the Channel Bonding Master.
- When a link down-trains to a single transceiver, change the CHAN_BOND_MODE to "OFF" via the DRP.
NOTE: All Xilinx transceivers also behave this way, so similar precautions should be taken.
AR# 30042
Date 12/15/2012
Status Active
Type General Article
  • Virtex-5 FXT
  • Virtex-5 LXT
  • Virtex-5 SXT
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  • Virtex-5 TXT
  • Virtex-6 CXT
  • Virtex-6 HXT
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