VLSI Síntese RTL 1

FEUP/DEECFebruary 2015

RTL Synthesis

João Canas Ferreira

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Contents

Includes figures from:Douglas J. Smith, HDL Chip Design

Synopsys, Design Compiler User Guide

General overview of the synthesis process Cadence RTL Compiler

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Top-down refinement

Progressive refinement of the descriptionsLower levels are increasingly more detailed

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RTL descriptions

Register transfer level Description involves registers and combinational circuits Synchronous systems (one or more clock signals)

It is important to describe the implementation explicitly in these terms

R RCombinational

clk

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Main steps

[Translation] HDL → internal representation of data and control flow

[Generic optimizations] Function inlining Constant propagation Loop unrolling

[Logic optimization] Logic synthesis Optimization of combinational circuits Retiming

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RTL synthesis

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Simplified model of design flow process

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Logic optimizations

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Technology mapping (1)

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Technology mapping (2)

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Electrical environment (1)

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Electrical environment (2)

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Conteúdo

Includes figures from :Douglas J. Smith, HDL Chip Design

Synopsys, Design Compiler User Guide

General overview of the synthesis process Cadence RTL Compiler

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Work flow

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Elaboration

This step includes:

Setup of internal data structures

Register inferencing

High level optimizations

dead code removal

Semantic verifications

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Naming

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Information hierarchy

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Constraints (1)

set output_load [get_attribute capacitance [find /libraries/gscl45nm/ -libpin INVX4/A] ]

set_attribute external_pin_cap ${output_load} /designs/${DESIGN}/ports_out/*

(Synopys Design Compiler)

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Signal delays

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Constraints (2)

set clock [define_clock -period 2000 -name clk [clock_ports]] #definition of clock signal

external_delay -input 0 -clock clk [find / -port ports_in/*] # input delaysexternal_delay -output 0 -clock clk [find / -port ports_out/*]

set_attribute slew_rise 400 [find / -clock clk] # assumed by cell libraryset_attribute slew_fall 400 [find / -clock clk]

set_attribute external_driver [find [find / -libcell INVX4] -libpin Y] \/designs/mips/ports_in/* # input pins

set_attribute external_driver "" [find / -port clk] # ideal clock

(Synopys Design Compiler)

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Interaction with physical synthesis

One of the possible work flows