为什么工具不能直接进入IDELAYCTRL

rmcg189写道：
ug190的第342页说“使用IDELAYCTRL模块的最有效方法是定义和锁定设计中使用的每个IDELAYCTRL实例的位置...... Xilinx强烈建议使用带有LOC约束的IDELAYCTRL”，但UG看起来并不像
为什么会这样说。
重点是什么？
为什么工具无论如何都不能直接进入IDELAYCTRL，而不被告知？如果没有它，IODELAY就没用了。谢谢。
这个布局器很可能太愚蠢了，无法确定每个基元的位置。
----------------------------是的，我这样做是为了谋生。



以下为原文

rmcg189 wrote:

Page 342 of ug190 says "The most efficient way to use the IDELAYCTRL
module is to define and lock down the placement of every IDELAYCTRL
instance used in a design....Xilinx strongly recommends using
IDELAYCTRL with a LOC constraint", but the UG doesn't seem to say
anywhere why this is the case. What's the point? And why don't the
tools just conenct up the IDELAYCTRLs anyway, without being told to?
The IODELAY is useless without it.

Thanks.

It's likely that the placer is just too friggin' stupid to figure out where to locate each primitive. 
----------------------------Yes, I do this for a living.