Regarding Prime time Static Timing analysis

[Arvindh19]

Hi people,

I found the following lines of code in the timing library file which is input to the Prime time

lu_table_template(delay_template_6x6) {
    variable_1 : input_net_transition;
    variable_2 : total_output_net_capacitance;
    index_1 ("1000.0, 1001.0, 1002.0, 1003.0, 1004.0, 1005.0");
    index_2 ("1000.0, 1001.0, 1002.0, 1003.0, 1004.0, 1005.0");

Can someone help me as to what the look up table is about as I am very confused with the variable 1,2 and the index_1 and 2 value


Regards
Arvindh.S

 

[rca]

a liberty file provide the timing (also area, power...) of internal path of a cell/macro.
for example the timing to go from a input A to output Q of a buffer is function of the input transition on seen on pin A, and the output load seen by the pin Q, then the tools based on the trans/load, used the lock-up table to know the propagation delay, rise/fall time...

in your case, the value provided could be for info, you need to check in the file where "delay_template_6x6" is used which values are given for index_1 and index_2, sometime there are similar, sometime completely different.

as well, the max value in the index_1 is normaly the max_transition, and similarly the max value of the index_2 is the max_capacitance, to indicate to the designer, that the timing is out the lock-up table, and the extrapolation could be (or is) erronous.

 

[Arvindh19]

Hi
Thank you for the reply. But I couldn't understand what you meant by capacitance value in index 2.
The max transition in index 1 is because of the capacitance value right?

 

[Prashanthanilm]

Hi people,

I found the following lines of code in the timing library file which is input to the Prime time

lu_table_template(delay_template_6x6) {
    variable_1 : input_net_transition;
    variable_2 : total_output_net_capacitance;
    index_1 ("1000.0, 1001.0, 1002.0, 1003.0, 1004.0, 1005.0");
    index_2 ("1000.0, 1001.0, 1002.0, 1003.0, 1004.0, 1005.0");

Can someone help me as to what the look up table is about as I am very confused with the variable 1,2 and the index_1 and 2 value


Regards
Arvindh.S

Hi Arvindh ,

The index_1 represents the value for variable_1 ie input_net_transition
Similar;y , index_2 represents output cap.

These values are derived using experiments and load spec .

By using this combination you will calculate the delays.
Eg : for 1000 input net tranistion and 1000 cap what is the delay?

You will have 6 X 6 matrix representing the delay values for these combination of slew and load