This document discusses RTL synthesis and provides an overview of the main steps in the RTL synthesis process. The document describes how RTL synthesis involves translating HDL code to an internal representation, performing generic optimizations like inlining and constant propagation, and logic optimization of combinational circuits. It also discusses how RTL synthesis maps optimized logic to target technologies and considers the electrical environment with constraints like timing and loads.

1. VLSI Síntese RTL 1
FEUP/DEEC
February 2015
RTL Synthesis
João Canas Ferreira

2. VLSI Síntese RTL 2
Contents
Includes figures from:
Douglas J. Smith, HDL Chip Design
Synopsys, Design Compiler User Guide
 General overview of the synthesis process
 Cadence RTL Compiler

3. VLSI Síntese RTL 3
Top-down refinement
Progressive refinement of the descriptions
Lower levels are increasingly more detailed

4. VLSI Síntese RTL 4
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 R
Combinational
clk

5. VLSI Síntese RTL 5
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

6. VLSI Síntese RTL 6
RTL synthesis

7. VLSI Síntese RTL 7
Simplified model of design flow process

8. VLSI Síntese RTL 9
Logic optimizations

9. VLSI Síntese RTL 10
Technology mapping (1)

10. VLSI Síntese RTL 11
Technology mapping (2)

11. VLSI Síntese RTL 12
Electrical environment (1)

12. VLSI Síntese RTL 13
Electrical environment (2)

13. VLSI Síntese RTL 14
Conteúdo
Includes figures from :
Douglas J. Smith, HDL Chip Design
Synopsys, Design Compiler User Guide
 General overview of the synthesis process
 Cadence RTL Compiler

14. VLSI Síntese RTL 15
Work flow

15. VLSI Síntese RTL 16
Elaboration
This step includes:
 Setup of internal data structures
 Register inferencing
 High level optimizations
 dead code removal
 Semantic verifications

16. VLSI Síntese RTL 17
Naming

17. VLSI Síntese RTL 18
Information hierarchy

18. VLSI Síntese RTL 19
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)

19. VLSI Síntese RTL 20
Signal delays

20. VLSI Síntese RTL 21
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 delays
external_delay -output 0 -clock clk [find / -port ports_out/*]
set_attribute slew_rise 400 [find / -clock clk] # assumed by cell library
set_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)

21. VLSI Síntese RTL 23
Interaction with physical synthesis
One of the possible work flows