PD Inputs

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Physical Design Input Files

Physical Design Inputs

Netlist (.v or .vhd)

It is the combination of sequential elements and their logical connectivity.

Netlist contains

Std. Cell instance – Name & Drive Strength
Macros & Memories instances

Netlist also consists of

Ports of Standard Cells and Macros
Interconnection details

Eg of a Netlist:

Module half-adder (C,S,A,B);
Input A,B;
Output C,S;
AND2 U1(.Y(C), .A(A), .B(B));
EXOR U2(.Y(S), .I1(A), .I2(B));
Endmodule

Constraints

Types of Constraints

Design Rule Constraints
Optimization Constraints

— Design Rules from the Fab.

Max. Cap./ Transition/Fanout
Clock Uncertainties

— Optimization Constraints from the designer

Timing Constraints/ Exceptions
Delay Constraints (Latency, Input Delay,Input Transition, Output Load and Output Transition)
Power and Area Constraints
System interface

Synopsys Design Constraints (SDC)
— Timing Constraints

Clock Definition (Time Period, Duty Cycle)
Timing Exceptions (False Paths,Asynchronous Paths)

— Non-Timing Constraints

Operating conditions
Wire load models
System interface, Design rule constraints (DRVs - Max. Cap./ Transition/Fanout)
Area constraints, Multi-voltage and Power optimization constraints
Logic assignments

Liberty Timing File (.lib or .db)

— Cell Logical View/ The Timing Library
— Std. Cell lib, Macro lib, IO lib
— Gate Delay = function of input transition time and output capacitance.

LIB contains

Cell Type and Functionality
Delay Models (WLD/ NLDM/ CCS)
Pin/ Cell Timings and design rules
PVT Conditions
Power Details (Leakage and Dynamic)

.lib file Example:

Cell (AND2_3) {
area : 8.000
pin (o) {
direction : output;
timing () {
related_pin : “A”;
rise_propagation () }
rise_transition () }
function : “(A & B)”;
max_cap :
min_cap : }
pin (a) {
dir : input;
cap : ;
}

Library Exchange Format(LEF)

— Cell Abstract View/ The Physical Library
— Std. Cell LEF
— Macro LEF
— IO LEF

LEF contains

Cell Name, Shape, Size, Orientation & Class
Port/Pin Name, Direction and Layout Geometries
Obstruction/ Blockages
Antenna Diff. Area

.lef file Example:

Layer m1
Type routing
width 0.50;
End m1
Layer via
Type cut
End via
Macro NAND_1
Foreign NAND_1 0.00.00
Origin 0.00.00
Size 4.5 by 12.0
Symmetry x y;
Site core;
Pin A
Dir input;
Port
Layer m1 End

Technology Related files

Technology file

Defines Units and Design Rules for Layers and Vias as per the Technology
Name and Number conventions of Layers and Vias
Physical and Electrical parameters of Layers and Vias
E.g. Direction/ Type/ Pitch/ Width/ Offset/ Thickness/ Resistance/ Capacitance/ Max. Metal Density/ Antenna Rule/ Blockages/Design Rules
Manufacturing Grid definition
Site/Unit Tile definition
Technology file has to load before loading other LEF files since it holds the layer information for that particular technology
.tech.lef (Cadence Format)
.tf - technology file (Synopsys Format)

Interconnect Parasitic file

Used for layer parasitic extraction
Contains Layer/ Via capacitance and resistance values in a Lookup Table (LUT) format
Also used to generate parasitic formats for the extraction tools (e.g. nxtgrd, captbl)
Extraction tool formats are more accurate than interconnect parasitic formats
.ict - Interconnect Technology Format (Cadence Format)
.itf - Interconnect Technology Format (Synopsys Format)
.ptf - Process Technology File (Mentor Graphics Format)

— Map file

Useful if is there is 2 different naming convections in Technology file, LEF or Interconnect Parasitic file

TLU+ file

TLU+ file is a binary table format that stores the RC Coefficients. The TLU+ models enable accurate RC extraction results by including the effect of width, space, density and temperature on the resistance coefficients. The map file matches the layer and via names in the Milkyway technology file with the names in the ITF (Interconnect Technology Format) file.

The main functions of this file can be given as finding:

R,C parasitics of metal per unit length.
These parasitics are used for calculation Net delays.
If TLU+ files are not given, then these are extracted from .ITF file.
For loading TLU+ files, we have to load three files Max TLU+, Min TLU+ and Map file.
Map file maps the .ITF file & .tf file of the layer and via names.

Milkyway Library

Note: Milkyway library was used in ICC1 in ICC2 we called it as NDM (New data model)

Milkyway is a Synopsys library format that stores all of circuit files from synthesis through place and route all the way to signoff. Most Synopsys tools can read and write in the Milkyway format including Design Compiler, IC Complier, StarRCXT, Hercules, Jupiter & Prime Time.

The Milkyway database consists of libraries that contain information about your design. Libraries contain information about design cells, std cells, macro cells and so on. They contain physical descriptions and also logical information.

Milkyway provides 2 types of libraries that we can use
(i) reference lib and
(ii) design lib. Ref lib contains std cells and hard (or) soft macro cells which are typically created by vendors.

Ref lib contains physical info such as routing directions and the placement unit tile dimensions which is the width & height of the smallest instance that can be placed. A design lib contains a design cell which contains reference to multiple reference libraries (std cells & macro cells).
The most commonly used Milkyway views are CEL & FRAM. CEL is the full layout view and FRAM is the abstract view for place and route operations.

Power Specification File

— Power Modes & Power Domains
— Tie Up supply & Tie Low supply
— Power Nets & GND Nets

Optimization Directives

Don’t use

Cells that are not supposed to optimize

Size only/ use only

Upsizing/ Downsizing only with this list of cells

Design Exchange Formats

— List & locations of Components, Vias,Pins, Nets, Special nets
— Die dimensions, Row definitions, Placement and Bounding Box Data, Routing Grids, Power Grids, Pre-routes
— .def, .fp are the common formats