问题举例

Warning: The trip points for the library named xxx differ from those in the library named yyy. (TIM-164)

分析

刚开始了解liberty库时，我们知道 input transition和output load用于延迟查找表，确定cell delay。但是，进一步考虑transition到底是多少，如何计算。理论上从开始下降或者上升，到结束下降或者上升；但模型库里面，使用30%~70%，或者 10% ~ 90%来计算。

Syntax

input_threshold_pct_fall（or _rise） : trip_pointvalue ;
1

trip_point: A floating-point number between 0.0 and 100.0 that specifies the threshold point
of an input pin signal falling from 1 to 0. The default is 50.0.
Use the input_threshold_pct_fall (or _rise) attribute to set the value of the threshold point on
an input pin signal rising from 0 to 1. This value is used to model the delay of a signal
transmitting from an input pin to an output pin.

Syntax

slew_derate_from_library : deratevalue ;
1

derate : A floating-point number between 0.0 and 1.0. The default is 1.0.
Use the slew_derate_from_library attribute to specify how the transition times found
in the Synopsys library need to be derated to match the transition times between the
characterization trip points.

库xxx

  output_threshold_pct_fall : 50;
  output_threshold_pct_rise : 50;
  slew_derate_from_library : 0.5;
  slew_lower_threshold_pct_fall : 30;
  slew_lower_threshold_pct_rise : 30;
  slew_upper_threshold_pct_fall : 70;
  slew_upper_threshold_pct_rise : 70;

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库yyy

 slew_derate_from_library            : 1;
 slew_lower_threshold_pct_fall       : 10.0;
 slew_upper_threshold_pct_fall       : 90.0;
 slew_lower_threshold_pct_rise       : 10.0;
 slew_upper_threshold_pct_rise       : 90.0;
 input_threshold_pct_fall            : 50.0;
 input_threshold_pct_rise            : 50.0;
 output_threshold_pct_fall           : 50.0;
 output_threshold_pct_rise           : 50.0;

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库xxx即计算 input transition and delay时，（70-30）/ 0.5 = 80
库yyy即计算 input transition and delay时， (90-10) / 1 = 80
所以二者等价。