In the RocketIO Virtex-5 GTP Wizard v2.0 and later, some configurations are not allowed.
For example, in RocketIO GTP Wizard v1.10 I could choose a 125Mhz reference clock when the linerate is 3.75 Gbps.
However, in RocketIO GTP Wizard v2.0 a 125Mhz reference clock is no longer selectable in the GUI when linerate is 3.75 Gbps.
Why has this changed?
GTP performance has not yet been fully characterized when PLL_DIVSEL_FB=3.
It is not recommended to set PLL_DIVSEL_FB to 3.