ERROR:NgdBuild:604 - logical block 'dcfifo_component' with type 'dcfifo' could
not be resolved. A pin name misspelling can cause this, a missing edif or ngc
file, or the misspelling of a type name. Symbol 'dcfifo' is not supported in
target 'virtex4'.
会出现这样的错误,高手帮我看看怎么回事啊