Shulou(Shulou.com)06/01 Report--

In this issue, the editor will bring you about how to do physical aware synthesis and the points that need to be paid attention to. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

In terms of methodology, thanks to DEF for building a bridge between the front and back, DEF transmits the information of floorplan to the synthesis tool, so that it can consider the real "physical information" in logic optimization, and do placement and global route according to the constraints of DEF, estimate net delay according to the results of global route, and at the same time do congestion optimization to complete the so-called physical aware synthesis.

On the tool side, neither C nor S can escape the methodology, but there is a difference in the way it is implemented. In addition to setting physical-related variables, S's physical synthesis probably needs three additional things (here completely based on unreliable memory, if there is a fallacy, please correct it): 1) dc_shell-topo; 2) create MilkWay DB; 3) compile_ultra-spg. This article will take the Genus of C family as an example to explain how to do physical aware synthesis. The routines of speaking tools all start with input and output, and then expand one by one. The following picture is drawn from Genus physical RAK. (RAK is a series of simple lib,C home tools with multiple RAK, which can be downloaded on the C home website, and it is strongly recommended to download and learn).

In addition to lib/rtl/sdc, the input to Genus physical must also have tech lef/ std cell lef/ macro cell lef; DEF; QRC tech file.

LEF: tech lef/std cell lef/ RAM lef is provided by foundry and sub-block lef is provided by the backend.

With the command: set_attribute lef_library $lef_files read in, you must put tech lef first in lef file list; you must read all cell lef used, otherwise you will see a warning in log: "because the physical information of a cell is not available, the cell is set to unavailable." "

Genus reads the following information from LEF:

CAPACITANCE CPERSQ

EDGECAPACITANCE

RESISTANCE RPERSQ

SITE

WIDTH

Coupling capacitance

Capacitanceper unit of area

Fringing capacitance

QRC: QRC is provided by foundry and is an encrypted file.

Read in with the command: set_attribute qrc_table_file $qrc_files.

Genus reads the following information from QRC:

PROCESS_VARIATION

BASIC_CAP_TABLE

Width

Cc

Carea

Cfrg

DEF: floorplan information, provided by the backend, which the backend bosses say is the soul of Prunr, the cornerstone and the foundation of all success.

In Innovus, use Defout-floorplan-NoStdCell to write a DEF containing the following sections, with comments here.

In Genus, use the command read_def to read DEF file. Genus will check DEF the Quality and report the relevant warning when reading DEF. After reading DEF, it will generate the following summary report. Please correct the Error and Warning that need to be corrected.

After reading DEF, use the command check_floorplan to further check DEF the quality, and correct Error and Warning in time.

After the input is clean, you can command the tool to start doing logic optimization with physical information. Genus uses early physical, that is, to optimize with physical information from the very beginning. The whole optimization process of Genus physical consists of three steps: syn_gen-physical, syn_map-physical and syn_opt-physical/ spatial. It is recommended to write a db after each step of optimization. In debug, you can read the db of different stages according to your needs, such as the correlation of the front and rear module placement of debug. You can compare the GUI highlight module place with the module place of Innovus after reading the DB after syn_gen.

There are two kinds of flow in Genus physical. The difference between the two flow is:

Syn_opt uses different option, one is: syn_opt-physical. The other is syn_opt-saptial.

Syn_opt-physical will call Innovus to do placement and global route, and the result is legalize. If the backend eats the netlist + DEF written by Genus, it only needs run place_opt_design-incr.

Syn_opt-spatial uses the placement engine embedded in Genus to do placement and global route, the result is not legalize, the backend needs run full place_opt_design.

The relevant variables of the two flow are different, and users can choose the corresponding flow according to their own design, process and team composition.

After the synthesis is completed, you need check-integrated quality. For physical aware synthesis, you need to pay attention to overflow in addition to PPA. Here are two points:

Using report_timing-physical-gui can highlight a complete timing path in layout, which is the most basic trick of debug timing and is very effective. It can look at data flow, line and bufferring.

Report congestion can report the overflow, open the congestion map to see what causes congestion, and then prescribe the right medicine. For example, the congestion related to macro needs to go to the backend to confirm whether the floorplan needs to be adjusted; whether the structure-related congestion needs to set map_to_mux on these structures when synthesizing, so as to maintain the mux structure rather than replace it with a large number of OAI/ AOI; such as congestion caused by cell accumulation, find AE to confirm whether there are variables for the tool to push and disperse the cell in serious areas of congestion.

The above is the editor for you to share how to do physical aware synthesis and need to pay attention to, if there happen to be similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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