clock tree synthesis engines

encounter中时钟树综合的引擎有4个

CCOpt – Full Clock Concurrent Optimization (CCOpt). Use of CCOpt requires the Encounter_ccopt_GXL license. The command ccopt_design , without the –cts parameter, is used to invoke this.
CCOpt-CTS – Global skew balanced CTS using the CCOpt CTS engine. In EDI 14.2 and onwards,this is the default CTS engine when the clockDesign command is invoked. Existing users of CCOpt-CTS will be familiar with the ccopt_design –cts command. CCOpt-CTS can be used with a clock tree specification generated from SDC timing constraints, or for backward compatibility from a FE-CTS clock specification.
Legacy FE-CTS – Global skew balanced CTS using the FE-CTS engine. In EDI 14.1 and earlier,
this is the default engine involved by the clockDesign command.

Legacy Scripted CCOpt – Scripted CCOpt is a standalone executable with an EDI integration wrapper. Scripted CCOpt uses a separate database, timing engine and other support infrastructure. Documentation for using the integration wrapper to scripted CCOpt can be found in the Legacy Scripted CCOpt section. The remainder of this document discusses what is sometimes referred to as Native CCOpt in which the CCOpt-CTS and CCOpt technology is fully integrated as part of EDI executable

 CCOpt-CTS 目标是通过使用usefulSkew建立更加平衡稳定的时钟树，Legacy FE-CTS 目标是clock skew=0

在encounter 14.2版本之前，clock tree synthesis engines默认使用的是Legacy FE-CTS，由clockDesign命令调用；

encounter 14.2及以后的版本，clock tree synthesis engines默认使用的是CCOpt-CTS，同样可以由clockDesign，命令调用，并且等同于命令ccopt_design -cts。

ccopt_design -cts使用引擎CCOpt-CTS默认调用的spec文件为create_ccopt_clock_tree_spec命令产生的文件，为tcl格式；

clockDesign -specFile使用的spec文件为createClockTreeSpec命令产生的spec文件。

如果命令ccopt_design -cts想调用createClockTreeSpec产生的spec文件也可以，需要使用命令-ckSpec，也就是ccopt_design -cts -ckSpec File1，这样会把FE-CTS的指定文件翻译转换成ccopt-cts需要的tcl格式文件。

也就是说，14.2版本之后，会有两套时钟树综合的命令，使用遗留的旧命令可以调用新的引擎，但是新的命令不可以调用旧的FE-CTS引擎，所以想要灵活转换还是需要自己理解透彻。

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