DEF file in VLSI Design | Data Exchange Format

In this article, we will discuss a widely used and very popular file used for data exchange from one EDA tool to another tool. Yes, we are going to discuss the Design Exchange Format or DEF file which is having extension .def. In this article, we will discuss the use of the def file, what information this file contains and how the information is arranged in various sections. We will also discuss how can we generate this file.

Introduction:

DEF file is used to represent the Physical layout of an Integrated Circuit (IC) in ASCII format. A DEF file is strongly connected with the Library Exchange Format (LEF) file. So both files needed for a correct display of physical design. DEF file format was developed by Cadence Design System. Whenever we need to transfer the design database from one EDA tool to another EDA tool for further implementation or analysis, we use the DEF file to transfer the design data. For example IR analysis on PnR database or STA on PnR database we transfer the design database in form of DEF file.

A DEF file contains the design-specific information of the circuit and it is a representation of the design at any point during the physical design. DEF conveys logical design data and physical design data. 

Logical design data includes internal connectivity (represented by netlist), group information and physical constraints. Physical data includes placement location and orientation of components and routing geometry. 

Sections:

A standard DEF file contains mainly following sections and order of statement is also important.

[ VERSION statement ]

[ DIVIDERCHAR statement ]

[ BUSBITCHARS statement ]

[ DESIGN statement ]

[ TECHNOLOGY statement ]

[ UNITS statements ]

[ DIAAREA statement ]

[ ROW statement ]

[ TRACKS statement ]

[ CELLGRID statement ]

[ VIAS statements ]

[ NONDEFAULTRULES statement ]

[ COMPONENTS statement ]

[ PINS section ]

[ BLOCKAGE section ]

[ FILLS section ]

[ SPECIALNETS section ]

[ NETS section ]

[ SCANCHAINS section ]

[ GROUPS section ]

[ BEGINEXT section ]

END DESIGN statement

Here we will take a sample DEF file to describe the various sections of the file.

Header statement:

Figure-1: Header part of DEF file

In header part, version of DEF, Design name, Technology name, Units and Dia area are mentioned. 

ROW statement:

Syntax:

[ROW rowName siteName origX origY siteOrient [DO numX BY numY [STEP stepX stepY]] [+ PROPERTY {propName propVal} ...] ... ;] ...

Here is an example of row section of def file.

Figure-2: Row statement in DEF file

rowName: Specifies the row name for this row.

siteName : Specify the LEF site to use for the row

origX origY : Specify the location of first site in the row

siteOrientation : Specifies the orientation of all sites in the row

Do numX BY numY :

•Specifies the  repeating set of sites that create the row.

•One of value must be 1.

•If numY is 1, then row will be horizontal

STEP stepX  stepY :

•Specifies the spacing  between sites in Horizontal and Vertical row

Track statement:

Syntax:

[TRACKS [{X | Y} start DO numtracks STEP space [LAYER layerName ...] ;] ...]

Example:

Figure-3: Track statement in DEF file

Description:

{X | Y }  start   

•Specifies the direction and location of first track defined

•X indicates vertical lines and Y indicates horizontal line

•Start is the X or Y coordinate of first line

Do numtracks  

 Specifies  the number of tracks to create for  the grid

STEP space:

•Specifies the spacing between the tracks

LAYER layerName

•Specifies the routing layer used for this track

•We can specify more than one layer

GCell Grid statement:

Syntax:

[GCELLGRID {X start DO numColumns+1 STEP space} ... {Y start DO numRows+1 STEP space ;} ...]

Example:

Figure-4: Gcell statement in DEF file

Description:

{X | Y }  start   :

•Specifies the location of first vertical (x) and first horizontal (y) track

Do numColumns+1  :

Do numRows+1 :

•Specifies  the number of columns or rows  in the grid

STEP space:

•Specifies the spacing between the tracks

Via statement:

Example:

Figure-5: Via statement in DEF file

Description:

All vias consist of shapes on three Layers

1.A cut layer

2.Two routing (or masterslice) layers that connect through that cut layer   

NDR statement:

Syntax:

NONDEFAULTRULES numRules ;

{- ruleName

[+ HARDSPACING]

{+ LAYER layerName

WIDTH minWidth

[DIAGWIDTH diagWidth]

[SPACING minSpacing]

[WIREEXT wireExt]

} ...

[+ VIA viaName] ...

[+ VIARULE viaRuleName] ...

[+ MINCUTS cutLayerName numCuts] ...

[+ PROPERTY {propName propVal} ...] ...

;} ...

END NONDEFAULTRULES

Example:

Figure-6: NDR in DEF file

Description:

•It defines any nondefault rules used in this design that are not specified in the LEF file.

•This section can also contain the default rule and LEF nondefault rule definitions for reference.

Component section:

•It defines design components, their location, and associated attributes

•A big section in DEF file

Syntax:

COMPONENTS numComps ;

[– compName modelName

[+ EEQMASTER macroName]

[+ SOURCE {NETLIST | DIST | USER | TIMING}]

[+ {FIXED pt orient | COVER pt orient | PLACED pt orient

| UNPLACED} ]

[+ HALO [SOFT] left bottom right top]

[+ ROUTEHALO haloDist minLayer maxLayer]

[+ WEIGHT weight]

[+ REGION regionName]

[+ PROPERTY {propName propVal} ...]...

;] ...

END COMPONENTS

Example:

Figure-7: Component section in DEF file

Pin section:

•It defines external pins

•Each pin definition assigns a pin name for the external pin and associates the pin name with a corresponding internal net name

•The pin name and the net name can be the same.

Example:

Figure-8: Pin section in DEF file

Blockage section:

•Defines placement and routing blockages in the design

•PUSHDOWN : Specifies that the blockage was pushed down into the block from the top level of the design

Example:

Figure-9: Blockage section in DEF file

Special net section:

Syntax:

[SPECIALNETS numNets ;

[– netName

[ ( {compName pinName | PIN pinName} [+ SYNTHESIZED] ) ] ...

[+ VOLTAGE volts]

[specialWiring] ...

[+ SOURCE {DIST | NETLIST | TIMING | USER}]

[+ FIXEDBUMP]

[+ ORIGINAL netName]

[+ USE {ANALOG | CLOCK | GROUND | POWER | RESET | SCAN | SIGNAL | TIEOFF}]

[+ PATTERN {BALANCED | STEINER | TRUNK | WIREDLOGIC}]

[+ ESTCAP wireCapacitance]

[+ WEIGHT weight]

[+ PROPERTY {propName propVal} ...] ...

;] ...

END SPECIALNETS]

Example:

Figure-10: Special net section in DEF file

Net section:

Syntax:

NETS numNets ;

[– { netName

[ ( {compName pinName | PIN pinName} [+ SYNTHESIZED] ) ] ...

| MUSTJOIN ( compName pinName ) }

[+ SHIELDNET shieldNetName ] ...

[+ VPIN vpinName [LAYER layerName] pt pt

[PLACED pt orient | FIXED pt orient | COVER pt orient] ] ...

[+ SUBNET subnetName

[ ( {compName pinName | PIN pinName | VPIN vpinName} ) ] ...

[NONDEFAULTRULE rulename]

[regularWiring] ...] ...

[+ XTALK class]

[+ NONDEFAULTRULE ruleName]

[regularWiring] ...

[+ SOURCE {DIST | NETLIST | TEST | TIMING | USER}]

[+ FIXEDBUMP]

[+ FREQUENCY frequency]

[+ ORIGINAL netName]

[+ USE {ANALOG | CLOCK | GROUND | POWER | RESET | SCAN | SIGNAL

| TIEOFF}]

[+ PATTERN {BALANCED | STEINER | TRUNK | WIREDLOGIC}]

[+ ESTCAP wireCapacitance]

[+ WEIGHT weight]

[+ PROPERTY {propName propVal} ...] ...

;] ...

END NETS

Example:

Figure-11: Net section of DEF file

Summary:

Various section of DEF file explained with the example and syntax. It is important to understand the DEF file in order to debug the design and its to verify the components.

Thank you!