Cadence Liberate Characterization of Complex Logic Cells

Hi anurans

I wanted to generate automatically all cells definition (define_cell) and all arcs definition (define_arc) for all cells of the library in the template.tcl file. I put in this file after defining  slew, measure_slew, delay, set cell_list, indexes the following script:

 set  inputs {I A1 A2 A3 A4 I0 I1 S D SI SE CDN SD}    --- total inputs of cells in the library

 set  outputs {Z ZN Q}                                                          --- total ouputs of cells in the library  

 set  clockss { CP}

 set  asyncs { }    

define_cell \

          -input $inputs  -outputs  -clock $clocks  -async $asyncs \

          -constraint  constraint_template_11x11 \

          -delay         delay_template_11x11 \

          -power        power_template_11x11 \

        $cell_list

 define_arc \  

          - vector {RXXR} \                 -- assume the maximal inputs of a cell is 4  

          - related_pin $inputs \    

           - pin $outputs \    

           $cell_list  

 define_arc \  

         - vector {FXXF} \  

         - related_pin $inputs \    

         - pin $outputs \

        $cell_list  

It seems it does not function.

What is the best way to define all cells and its arcs?

Kind regards

BarPouy

Hello,

To generate all the cell and arc definitions, you may use (as Guangjun stated earlier): 

char_library -trial; //to generate a dummy .lib file, Then,

read_library existing.lib
write_template -verbose liberate_templates // to dump all the arcs found

This will generate all the arcs related to hidden, timing, constraints etc. If you had already done this, you should look at the log file for any possible issues. If its less descriptive, add following before char_library command : 

#####--------------------------------------------------------------------------------------------------------------------------------------------------
##### Debug variables
#####--------------------------------------------------------------------------------------------------------------------------------------------------
#select_index -style 1x1 ;# run only 1st point in table

set_var bisection_info 4 ;# print additional bisection search info to output log
set_var power_info 2 ;# print additional power calculation info of table's 1st point to file decks/po

set_var ski_enable 0
set_var extsim_save_passed all ;# save all run decks and output files
set_var extsim_save_failed all ;# save all run decks and output files
set_var extsim_save_verify 2 ;# save verify deck
set_var extsim_deck_dir [file normalize "Liberate_Out/decks"] ;# specify directory for SPICE decks and output files
set_var extsim_tar_cmd "" ;# disable tgz of simulation decks and run logs
#####-------------------------------------------------------------------------------------------------------------------------------------------------

liberate char.tcl |& tee char.log // your log file

This would give you a thorough look to the issues you have. May be you should do the debugging ONLY to the erroneous cells, otherwise you will end up having a very large deck file.

Anuradha

Hello,

Thank you for your suggestion.

I tried with >char_library -trial, however the "Command not found"! Maybe with >liberate char_library -trial ? 

Then I tried with my top scrip and generate only for one cell, as Guangjun suggested. A  .trial.ldb.gz file is generated. After ungzip of this file I tried to read it. >read_library thisFile.ldb (should be converted to .lib ?),  again, "Command not found"!

Regards

BarPouy

-trial is an option for char_library. Please read the manual on char_library command! I suggest you either take a Liberate training, or go though a RAK to understand Liberate flow/command.

Regards,

Guangjun

You are right, a training is very helpful! However at the moment I've not possibility to do that. Actually I read RAK, I will read through RAK again.

For one cell it seems I came further! Now I have this WARNING / ERROR.

WARNING (LIB-411): An estimated max load value of 2.8181e-16F will be used for slew: '7.61097e-09s' pin: 'Z' of cell: 'AN2d1' because the auto_index algorithm failed to determine the max load using bisection. This can occur when the inside-view algorithm cannot determine a valid vector. Add appropriate 'define_arc' commands specific to pin 'Z' and rerun.

*Error* (char_library -auto_index) : the maximum load for AN2d1:Z is smaller than the specified min_output_cap (2.8181e-16F <= 1.07555e-15F).  This problem might be caused by insufficient drive strength or a max_transition value that is too small. 

Regards

BarPouy

You are right, a training is very helpful! However at the moment I've not possibility to do that. Actually I read RAK, I will read through RAK again.

For one cell it seems I came further! Now I have this WARNING / ERROR.

WARNING (LIB-411): An estimated max load value of 2.8181e-16F will be used for slew: '7.61097e-09s' pin: 'Z' of cell: 'AN2d1' because the auto_index algorithm failed to determine the max load using bisection. This can occur when the inside-view algorithm cannot determine a valid vector. Add appropriate 'define_arc' commands specific to pin 'Z' and rerun.

*Error* (char_library -auto_index) : the maximum load for AN2d1:Z is smaller than the specified min_output_cap (2.8181e-16F <= 1.07555e-15F).  This problem might be caused by insufficient drive strength or a max_transition value that is too small. 

Regards

BarPouy

the message is very clear. have you tried anything following the message?

as a quick test, you may remove -auto_index and define your own load index, save the deck. if the error happens again, check the decks. run spectre on the decks and check if the waveform show expected transitions at all ports.

Regards,

Guangjun

BarPouy said:

the maximum load for AN2d1:Z is smaller than the specified min_output_cap (2.8181e-16F <= 1.07555e-15F)

Mmm.... how did you specify the min_out_cap ? When liberate fails to find appropriate max_cap means, your max_transition is not suitable for the auto_indexing calculation. The max_cap is always measured with respect to the max_trans defined in the template. You need to adjust it properly....

Anuradha

Thanks a lot!

I've not used -auto_index. I put manially all arcs for one cell in the template and run again. I get the same WARNING / ERROR.

I used

set_var max_transition 5e-08

This should be enough for an AN2d1, even in subthreshold regime.

Regards

BarPouy

Thank you anurans!

I increased the max_transition to 50 ns (set_var max_transition 5e-08) only to see what happen, actually it's too high even in subthreshold regime. As I designed and I did postlayout simulation (with Monte Carlo), the transition was much much lower.

Regards

BarPouy

As Guangjun advised then re-run the failed decks. Locate the failed sim.sp file in the deck folder. Remove save=nooutput from .sp file and : 

spectre sim.sp

then use viva to check the waveforms. You should see the failure of the cell given bisection search value.

Anuradha

I try to understand what you wrote. Aussuming the cell_nam is AN2d1. Do you mean I should generate AN2d1.sp in AN2d1 folder? Then 'remove save=nooutput from AN2d1.sp'. After that run spectre An2d1.sp. Finally check waveforms.

I've not viva license, it should be also possible with ADE_L /XL?

I will do that.

Thank you!

Regards

BarPouy

No, during the characterization you can save your simulation decks for debugging : 

set_var extsim_deck_dir /home/work_dir/decks_DDC_smth
set_var extsim_save_passed deck

(before char_library) !

This deck folder should report simulation data for each cell in separate folders which could be PASS or FAIL. Locate the failed folder of your failed cell. It should have the sim.sp file. 

ADX should be possible. Viva is their visualization tool....

Anuradha

1.Check the manual for correct sytanx and use these commands,

set_var extsim_deck_dir full-path-here

set_var extsim_save_failed deck

set_var exism_save_passed none

2. If your run has failed characterization at simulation stage, go to the deck dir. You will see saved deck dir or a tarball. Inside each sub dir, you will see a map.list. open this file you will see where the failure is. Find the deck (sim.sp)for the failed char, remove save=nooutput, then run spectra on it. 

3. Start viva with ade license. Open the simulation results and check the waveform.

4. Review the settings and variables in the deck-- are they the same as your own test bench? If not, either your test bench or the characterization settings need to be corrected.

Tip. select_index 2x2 may use min/max indecis, which makes the debug easier.

Guangjun

Hi Guangjun, Hi anurans,

Thank you for your tips. I'm following it.

Kind regards

BarPouy

Hello Guangjun

Automatically generation of the template (with defined cells) for the cells having the same inputs /outputs, e.g. AN2d1 /OR2d1 (inputs: A1 A2) can be doen. However, If I mix such cells with the cells having more inputs /outpus or other inputs /outputs, e.g. AOI21.d1 (inputs: A1 A2 A3) or DFd1 (inputs: D, clock: CP, output: Q), then the template will not be generated and gives ERROR (see please below). It's clear, if I write for each class of cells, having the same inputs / outputs, a separate define_cell,  then this issue does not occur. There is an example of generating automatically template in the page 48 to 50 of 'Virtuoso Liberate Reference Maual', Version 18.1, section 'TCL Command File'. It shows that it might be possible to generate template of different class of cells like {NAND2X4 NOR2X2 DFFX1} just with one general define_cell.

What is my mistake?

Thanks!

Kind regards

BarPouy

ERROR (LIB-520): (char_library): The pin 'D' is not defined for cell 'AN2d1'. This cell will be ignored. Check the netlist and make sure it is consistent with 'define_cell' command.

ERROR (LIB-203): (char_library): Cell 'AN2d1' is scheduled for characterization but has no netlist, has an empty subckt or has no port on the subckt. This cell will be skipped. Check the netlist and rerun.

ERROR (LIB-520): (char_library): The pin 'CP' is not defined for cell 'DFd1'. This cell will be ignored. Check the netlist and make sure it is consistent with 'define_cell' command.

ERROR (LIB-203): (char_library): Cell 'DFd1' is scheduled for characterization but has no netlist, has an empty subckt or has no port on the subckt. This cell will be skipped. Check the netlist and rerun.

ERROR (LIB-520): (char_library): The pin 'D' is not defined for cell 'OR2d1'. This cell will be ignored. Check the netlist and make sure it is consistent with 'define_cell' command.

ERROR (LIB-203): (char_library): Cell 'OR2d1' is scheduled for characterization but has no netlist, has an empty subckt or has no port on the subckt. This cell will be skipped. Check the netlist and rerun.

WARNING (LIB-961): (char_library): Leakage deck initialization was requested using '.ic', but the 'leakage_sim_duration' was set to '0'. This may lead to unexpected leakage characterization results. Change 'leakage_sim_duration' to a positive non-zero value in seconds or change the setting of 'set_sim_init_condition' and rerun.

Building library database

Processing cell: AN2d1

Processing cell: DFd1

Processing cell: OR2d1