General Description: When I use the KEEP_HIERARCHY constraint in a design and the design contains IBUFs/OBUFs that are instantiated in separate hierarchical levels, NGDAnno reports an error similar to the following:
"ERROR:Anno:297 - fragment ("i" (tag=6 in view "FRAGCOVERED")) has parent ("level1" (tag=0 in view "FRAGCOVERED")) does not match component's parent: component (i (IOB (0))) parent ("lower_level_hierarchy" (tag=1 in view "FRAGCOVERED"))"
NGDAnno will output an NGA file. NGD2VHDL and NGD2VER can be run on the NGA to create a valid simulation netlist, but the netlist will be flattened.
This problem will be fixed in 5.1i Service Pack 3, which will be available in mid-December, 2002.
Until 5.1i Service Pack 3 is released, the only way to work around this problem is to instantiate all buffers in the top level. If this cannot be done, only a flattened netlist can be generated until Service Pack 3 is installed.