MAP produces internal error when the OFFSET OUT constraint is applied.
INTERNAL_ERROR:Pack:pksbatsdesign.c:1189:1.42 - No Xdm objects (or unexpected resolution specifiers) for CLKGRP=xaui0_refclk_p (ResSpec: NULL) with references:
Removing the following OFFSET constraint allows MAP to complete.
NET "gmii_txd*" OFFSET = OUT 4 AFTER xaui0_refclk_p REFERNCE_PIN "gmii_tx_clk" RISING;
The constraint is valid, since the clock "xaui0_refclk_p" drives a GTP block.
Why does it cause an internal error?
This is a Pack issue and has been fixed in 12.3.
The design with OFFSET constraints will pass MAP in 12.3.
However, it also involves a problem where the PERIOD constraint on the GTP refclk input is not propagated to the output clock.
Thus an OFFSET out constraint for the path clocked by the GTP output clock is not analyzed. This issue is fixed in ISE 13.2.