关于set_dft_signal里的参数的问题

lobol

想问一下，-view
existing_dft | spec，这两个选项有什么区别，在进行扫描插入的时候该如何设置？比如所我一个design里，有一个全局的reset和clock信号，在模块端口有reset和clock引脚。另外还加了tm，se，si，so的空端口，对于这些reset, clock, tm,se,si和so，应该设置成existing_dft还是spec呢？


man下该命令，原文是如下，不是很理解，故提问，还请高人帮人解疑下……
Indicates the view to which the specification applies. Valid views are

existing_dft: This implies that the specification refers to the existing usage of a port. For example, to describe that port A is used as a scan enable, enter
set_dft_signal -view existing_dft -port A -type ScanEnable
This is used when working with DFT inserted designs.

spec (default) : This implies that the specification
refers
to ports
that the tool must use during DFT insertion. For example, to prescribe that port A is used as a test enable, enter
set_dft_signal -view spec -port A -type ScanEnable
This is used when preparing a design for DFT insertion