**ERROR: (TA-152): A latency path from the ‘Fall’ edge of the master clock at source pin…

Error Code

TA-152

在数字IC后端实现innovus中我们经常会看到这类Error，具体信息如下所示。

Error Message

**ERROR: (TA-152): A latency path from the ‘Fall’ edge of the master clock at source pin clk’ to the ‘Rise’ edge of generated clock ‘gen_clk’ at pin ‘gen_clk’ cannot be found. You must modify your create_generated_clock constraint to be consistent with the network topology. The analysis will continue using 0ns source latency for generated clock ‘gen_clk’. For backward compatibility with earlier releases or to remove the edge-to-edge sufficiency checking, you should set the global ‘timing_enable_genclk_edge_based_source_latency’ to false

**ERROR: (TA-152): A latency path from the ‘Rise’ edge of the master clock at source pin ‘clk’ to the ‘Fall’ edge of generated clock gen_clk’ at pin ‘gen_clk’ cannot be found. You must modify your create_generated_clock constraint to be consistent with the network topology. The analysis will continue using 0ns source latency for generated clock ‘gen_clk’. For backward compatibility with earlier releases or to remove the edge-to-edge sufficiency checking, you should set the global ‘timing_enable_genclk_edge_based_source_latency’ to false

在innovus中出现这个错误，如果是第一次遇到，我们要学会根据工具提示的信息去分析。这里报的是generated clock的rise edge无法从master clock的fall edge获取到。

所以这类问题都是SDC中关于分频时钟的定义有问题。对于后端工程师来说，你可以直接反馈给前端或中端工程师。当然大家也可以研究到底应该怎么去改sdc。

上图所示的三分频电路的时钟应该通过-edge {1 5 7} 来定义，这样工具就不会报这个错误了。

同理，如果source clock经过反相后到底分频寄存器的，那么下图所示的generated clock定义也会有问题。

这个错误不解决带来的后果，欢迎大家交流讨论下。100%是需要解决的！