sdc about “the inverted output clock”

看到一段话，“This is correct, because the inverted output clock only allows half a cycle for setup - the hold calculation will get the other 10.0 ns”
为啥是这样子的，好奇怪啊。各种大神来拍砖把。55

额。LZ傻了，看书不仔细，原来是launch clock 是 rising edge， capture clock是用 falling edge，所以check setup只能用一半period的time。