Liberate for library file

Hi Fengye,

When using write_verilog, out pins must have a 'function' attribute. for flip/flops, a 'ff' group must also be created inside the cell section. If these are not auto-created, you have to use the user_data flow when generateing the .lib file.

Regards,

Guangjun

Hi Guangjun,

Thanks a lot for your reply.  The function attribution of my flipflop cell cannot auto-created. For the usage of the user_data, I don't know if I need to prepare a verilog file as a user_data file. Can you give me some suggestions?

Regards,

Fengye

Hi Guangejun,

I have upload my test case with the ftp server. If you have time, I hope you can help me look into it.

Regard,

Fengye

Is this a valid arc for this cell?

cell=balloon_sim_nognd, pin=NRESTORE, related_pin=CK, timing_type=removal_rising, when=(!D * !SAVE), rise_constraint

Hi Guangjun,

This is the error  timing arc I have said. I am not sure if it's not valid for the cell.  NRESTORE is low-active and maybe an asynous input pin.  So, I use the write_template to get all the arcs from the incomplete lib file and run agagin with the given arcs, which the above error removal arc is eliminated.

According to the definition, " Removal time for sequential cells is the minimum length of time at which the set or reset signal must remain after the active edge of the clock to ensure correct functioning of the cell. " I don't understant why there are so many arcs.

Regard,

Fengye

Hi Guangjun,

After I set 'NRESTORE' as a Synchronous input, there are still more problems about the arcs. The all arcs generated by Liberate has a possibility of error. If it's true to eliminate some of them.

Regared,

Fengye

Hi Guangjun,

I looked the Liberate manual and find some commands like

"read_library TSMC_balloon_ss_0p99v_125c_ecsm.lib
# set timing check variables
set vital_timing_violation_format "Tviol_edge"
set vital_recrem_violation_format "Rviol_ref_edge"
set vital_timing_info_format "Tinfo_ref_edge"
set vital_recrem_info_format "Rinfo_ref_edge"
# Output a Vital file
write_vital TSMC_balloon_ss_0p99v_125c_ecsm.vhd"

The the vhd file has some reminder about error, you know how this can help me deal this problem.

Thanks a lot!

Regards,

Fengye

Hi Fengue,

You can not simply ignore a failed arc characterisation. 'removal' constraint is like 'hold'. You should ask the designer to clarify whether this arc is valid. If it is, you can save the failed deck and do debug. there are suggestions in the logfile, which should be tried first. You can also save the passsed deck and use them for debug reference.

For the function, you may have to add it yourself, as this cell may not be normal "standard", but a custom digital. the right function can only be provided by the cell designer and the STA digital engineer. You can also use a similar cell as a reference.

Guangjun 

Is this the same library? If so, it is meant to fail, as your library is not complete.

If 'NRESTORE' is NOT Synchronous, then you can not define it as Synchronous.

one quick question: does this cell pass characterisation on other corners, eg. TT?

Hi Guangjun,

Thanks for your reply! 'NRESTORE' may be asynchronous.  The error removal arc may be eliminated. Then the lib can be gennated without error, but still with warnning about "write_verilog". This same case can happer at SS,TT FF cornner. 

When the lib without above removal arc is used for synthesis, some warnning shows the balloon cell is unusable. This is the reason I want to analyze the correctness of the lib file.

After you tried that, are the complete lib file generated?

Regard,

Fengye 

Hi Guangjun,

Thanks for your reply! 'NRESTORE' may be asynchronous.  The error removal arc may be eliminated. Then the lib can be gennated without error, but still with warnning about "write_verilog". This same case can happer at SS,TT FF cornner. 

When the lib without above removal arc is used for synthesis, some warnning shows the balloon cell is unusable. This is the reason I want to analyze the correctness of the lib file.

After you tried that, are the complete lib file generated?

Regard,

Fengye 

Hi Fengye,

I saw the failed arc, but did not try to debug it. It can be very time consuming and may need knowledge about the logic behavior of the cell. In any case, you need to find out if this arc is valid.

It is not clear to me that the "unusable" warning is due to the removed "removal". What synthesis/tool are you talking about? can you get help on why this warning is issued? in general, a missing arc does not always cause problem. 

regards,

Guangjun

Hi, Guangjun,

Thanks again. I really grateful that you spend your precious time help me. Your suggestions have a great influence on me. The synthesis tool is RTL complier. For the imcomplete balloon library, I delete some arcs about from  NRESTORE  to Q,and add function attribution manually. The synthesis can run normally. But I don't know if it will influence the later automatic Place and route. I will debug and analyze the related arcs to see if it's invalid.

Thanks again!

Regard,

Fengye

Hi Fengye,

I tried to debug the failed arc. Spice simulation does not show valid transition or expected signal level for  pin=NRESTORE, related_pin=CK, timing_type=removal_rising, when=(!D * !SAVE), rise_constraint. If the cell is designed correctly, then this is not a valid arc. However, it is designer who can tell. If an auto-generated arc is invalid, you can still use the auto-generation flow, but add define_arc -ignore in the template, eg,

define_cell \
-clock { CK } \
-async { SAVE NRESTORE } \
-input { D } \
-output { Q } \
-pinlist { CK D SAVE NRESTORE Q } \
-delay delay_template_7x7 \
-power power_template_7x7 \
-constraint constraint_template_3x3 \
-mpw mpw_template_3x1 \
balloon_sim_nognd

define_arc \
-type hold \
-when "!D * SAVE" \
-pin NRESTORE \
-related_pin CK \
-vector {RxxRx} \       ;#mtach the order to -pinlist

-ignore \
balloon_sim_nognd

-----------------------------------------------------------------

Is this a retention cell with balloon latch? Please refer to this link for syntax of such cells. You may search for "balloon" to find related information. In particular, there is an example on p.485.

https://media.c3d2.de/mgoblin_media/media_entries/659/Liberty_User_Guides_and_Reference_Manual_Suite_Version_2017.06.pdf

According to Liberate manual, the ff/latch group for retention cells have to be added by user. This can be done with -user_data option in write_library command. I believe you already know by now how to use the user_data flow.

one important note: when you use user_data during write_library, you may want to change setting for cell_use_both_ff_latch_groups, eg setting it to 2.

Looking through your script, there are two incorrect settings for power/ground, which should be,

set_gnd -type pwell VPW 0
set_vdd -type nwell VNW 0.99

Regards,

Guangjun

Hi, Guangjun,

I really appreciate your solutions. Your reply is so detailed. With you suggestion and the documment you provided, I think I can get final solution about the characterization of the retention cell.

Thanks again!

Regard,

Fengye