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In addition to the setup and hold checks already performed during back-annotation, NGDAnno creates a Guaranteed Setup and Hold Check (GSUH) primitive between each input pad that drives an IOB register and global clock pad that drives the register's clock pin. The GSUH values match closely with the pin-to-pin setup and hold values published in The Programmable Logic Data Book. Only device families and configurations that have published pin-to-pin setup and hold values are supported by the new GSUH primitive.
This checking only occurs for IOBs and clock configurations that meet the requirements for a particular device. Generally, devices require an externally driven clock that uses the global clock resources to clock an input IOB register. Older device families may not support all GSUH combinations.