The magic of StarRC

In the entire R2G process, the parasitic parameter extraction (StarRC) is relatively non-existent. Most of the time, engineers just use this tool to flash SPEF. Don't pay too much attention. This in itself is actually a good thing, and it proves the high stability of the parameter extraction tool in reverse!
However, no matter how small a tool is, there is room for digging. StarRC is a small tool worthy of careful attention. It does not say much, but does a lot. Through some special adjustments, you can also get extra gains. Without further ado, ICer GO!

Introduction

StarRC's parasitic parameter extraction can be used as a sign-off standard. Compared with APR, it usually has the following advantages (complete) potential (preparation)

• metal fill handle
• half-node scale factor
• light-base layer and lower metal support. like: poly, active, contact, M1 etc.
• For resistance scaling by temperature
  , the common impact mainly comes from metal filll. Metal fill is a common problem dealing with the density of chip tape-outs. Unlike conventional APR operations, metal fill is usually done in caliber (inside the GDS tool), although the process done in the APR tool has also been popular in history. But in terms of processing efficiency and independence, metal fill is indeed the strength of GDS tools such as caliber.
  Since metal fill is generated on-site based on real GDS data (APR usually uses LEF/MW files), various factors are mixed together, and metal fill usually brings about some RC parameters and the influence of winding/

Open/short GUI positioning function of StarRC

On a regular starRC run database, usually two files are generated

• shorts_all.sum
• Opens.sum
  users can locate the short/open problems caused by the merger of information such as APR database and metal fill by reading these two files. Of course, these two reports will also contain the original short//open information of the APR database.
  Based on the above, starRC can judge the short/open problem in the extraction object database. Using this function, StarRC can export the MW/NDM database and check the short/open in the GUI. The specific process is as follows:

1. Complete normal starRC extraction
2. Generate a GUI-debuggable database based on the following starRC command

*** * for icc user
*** DEBUG_MILKYWAY_DATABASE: my_design 
* for icc2 user
DEBUG_NDM_DATABASE: my_design 
* this path need to match the normal starRC command setting
STAR_DIRECTORY: star
** * for all nets comamnd:
** NETS: *  
NETS: net1 net2 net3
3. 运行命令，生成可以debug的MW/NDM数据库
> StarXtract -Display short_regions star_cmd_debug
4. 打开MW/NDM数据库进行查验

short GUI debug example

In the short_all.sum file of starRC, there is the following description,

Here is a short of net and blockage. At this time, use the following command to open the debug database,

and then it will focus on the specified position, and you can see the following information

The three nets shown in the short report can be seen here. The SYNPSYS_FLOAT marked here is a metal fill marking method. Compared with GDS, you can see this detail (PS: In order to save resources, StarRC only keeps the
adjacent metalfill information)

open GUI debug example

For open net, according to the actual logical connection relationship, a short connection (unopen) will be selected from the existing winding resources, and a small resistance will be applied to the short connection based on the process information, such as here: in the resistance=0.01, width=100
description The RCG means: resistively connected group

starRC reconnects the output pin and the open net together by using a default (very small) resistor, so that for STA, there will not be a large open circuit delay. Therefore, it is obviously more reasonable to use a virtual connection with a small resistor than to keep it open.

A simple schematic is shown below: Make the connection through a small resistor

spef RC information comparison

Usually both APR tools and StarRC can generate spef, but StarRC's SPEF can be used as a sign-in. In view of the above, APR's spec usually cannot be used as a sign-in. In order to promote the timing analysis, it is necessary to make the RC information of the APR and the receipt as consistent as possible. Here, the user needs to compare the spef extracted by APR and StarRC, and then reasonably configure the RC scaling of APR based on the results, so as to obtain the RC information in the APR approaching the sign-off stage, which can achieve twice the result with half the effort for optimizing timing .

Order:StarXtract -compare_parasitics APR_SPEF SIGNOFF_SPEF

StarRC will compare from three dimensions:

• net total cap
• net coupling cap
• p2p resistance

At the top of the comparison return information, there will be three-dimensional comparison mean (mean) and variance (std) information

The variance is the average of the sum of the squares of the differences between each data and the average, and is usually used to describe the dispersion of the data. The smaller the variance result, the smaller the dispersion and the higher the consistency. For example, the following tcap
difference

Among the above information:

• A positive value means: APR is greater than signoff
• Negative value means: APR is smaller than signoff

For different APR tools, please use the following commands to configure

• invs: Users can adjust create_rc_cornerthe RC extraction of APR to achieve a value closer to signoff by adjusting the following.
  

• ICC/ICC2: Users can set_extraction_optionsconfigure RC scaling through commands
  

[Knock on the blackboard to draw key points]

StarRC can read more GDS-related information than APR, and can follow the original work when doing extraction, and can assist the R2G design process and speed up positioning. It is a small tool worth playing with

References

Synopsys StarRC User Guide