Type: Answers

Type: Errata

Area: Intellectual Property

LL 40GbE 40GBASE-KR4 IP Core Link Training is Slow When Adaptation is Enabled


If you enable CTLE adaptation in your Low Latency 40GbE 40GBASE-KR4 IP core variation, Link Training might not complete within 500 ms as required by the Ethernet specification. In that case, the IP core indicates a link training failure, and equalization might not be trained optimally for the link.


To work around this issue, disable CTLE adaptation and use a fixed CTLE value during Link Training. To set a fixed CTLE value, set the values of the following registers. Note that although they are documented in the user guide as Reserved, you can in fact write to them.

  • 0x0D0[22:20]: Set this register field to the value of 0x100.
  • 0x0D0[28:24]: Set this register field to the desired CTLE value.

This issue is fixed in version 15.0 Update 1 of the LL 40-100GbE IP core.