Xilinx Synthesis Technology User Guide

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XST User Guide FSM Inputs Registered inputs are described using internal signals, which are assigned in the sequential process. State Encoding Techniques XST supports the following state encoding techniques. • Auto • One-Hot • Gray • Compact • Johnson • Sequential • User Auto In this mode XST tries to select the best suited encoding algorithm for each FSM. One-Hot One-hot encoding is the default encoding scheme. Its principle is to associate one code bit and also one flip-flop to each state. At a given clock cycle during operation, one and only one state variable is asserted. Only two state variables toggle during a transition between two states. One-hot encoding is very appropriate with most FPGA targets where a large number of flip-flops are available. It is also a good alternative when trying to optimize speed or to reduce power dissipation. Gray Gray encoding guarantees that only one state variable switches between two consecutive states. It is appropriate for controllers exhibiting long paths without branching. In addition, this coding technique minimizes hazards and glitches. Very good results can be obtained when implementing the state register with T flip-flops. 2-184 Xilinx Development System
Compact HDL Coding Techniques Compact encoding consists of minimizing the number of state variables and flip-flops. This technique is based on hypercube immersion. Compact encoding is appropriate when trying to optimize area. Johnson Like Gray, Johnson encoding shows benefits with state machines containing long paths with no branching. Sequential Sequential encoding consists of identifying long paths and applying successive radix two codes to the states on these paths. Next state equations are minimized. User In this mode, XST uses original encoding, specified in the HDL file. For example, if you use enumerated types for a state register, then in addition you can use the enum_encoding constraint to assign a specific binary value to each state. Please refer to the “Design Constraints” chapter for more details. XST User Guide 2-185
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Xilinx Synthesis Technology (XST) U
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About This Manual Manual Contents T
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Resource Description/URL About This
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Conventions Typographical This manu
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Contents About This Manual Conventi
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Contents 8-bit Shift-Left Register
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Contents Dividers .................
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Contents Verilog Flow: ............
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Contents Sequential Process with a
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Introduction Architecture Support X
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Introduction 4. Set the desired Syn
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Figure 1-1 View Synthesis Report In
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HDL Coding Techniques This chapter
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HDL Coding Techniques The following
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Table 2-1 VHDL and Verilog Examples
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Signed/Unsigned Support Registers H
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Flip-flop with Positive-Edge Clock
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VHDL Code HDL Coding Techniques Fol
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IO Pins Description CE Clock Enable
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Log File HDL Coding Techniques The
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HDL Coding Techniques Verilog Code
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HDL Coding Techniques 4-bit Latch w
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Tristates Log File HDL Coding Techn
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Counters HDL Coding Techniques XST
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HDL Coding Techniques 4-bit Unsigne
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HDL Coding Techniques entity counte
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Verilog Code HDL Coding Techniques
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HDL Coding Techniques 4-bit Unsigne
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Accumulators HDL Coding Techniques
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HDL Coding Techniques • shift mod
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HDL Coding Techniques 8-bit Shift-L
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Dynamic Shift Register module shift
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library IEEE; use IEEE.std_logic_11
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neither Full nor Parallel module no
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Related Constraints Related constra
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HDL Coding Techniques entity mux is
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Decoders Log File HDL Coding Techni
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VHDL (One-Cold) Following is the VH
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VHDL Following is the VHDL code. li
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Priority Encoders Log File HDL Codi
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Verilog Logical Shifters HDL Coding
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Example 1 HDL Coding Techniques The
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Verilog Arithmetic Operations Follo
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Unsigned 8-bit Adder HDL Coding Tec
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HDL Coding Techniques Verilog Follo
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Simple Signed 8-bit Adder HDL Codin
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Unsigned 8-bit Adder/Subtractor HDL
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Comparators (=, /=,=) HDL Coding Te
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HDL Coding Techniques this, XST can
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Dividers HDL Coding Techniques VHDL
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B C A OPER +/- RES OPER X8984 HDL C
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HDL Coding Techniques • RAM descr
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HDL Coding Techniques entity raminf
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HDL Coding Techniques VHDL The foll
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HDL Coding Techniques Verilog The f
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HDL Coding Techniques VHDL The foll
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Page 157 and 158: VHDL Following is the VHDL code for
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Page 161 and 162: Verilog HDL Coding Techniques Follo
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Page 165 and 166: HDL Coding Techniques Single-Port R
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Page 169 and 170: VHDL HDL Coding Techniques Followin
Page 171 and 172: Dual-Port RAM with Asynchronous Rea
Page 177 and 178: HDL Coding Techniques Dual-Port RAM
Page 181 and 182: HDL Coding Techniques architecture
Page 183 and 184: HDL Coding Techniques Dual-Port RAM
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Page 197 and 198: Inputs Next State Function RESET CL
Page 199 and 200: FSM with 1 Process HDL Coding Techn
Page 201 and 202: Inputs FSM with 2 Processes HDL Cod
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Page 207: State Registers HDL Coding Techniqu
Page 211 and 212: Black Box Support Log File HDL Codi
Page 215 and 216: FPGA Optimization Introduction This
Page 217 and 218: Macro Generation • Number of Cloc
Page 219 and 220: Multiplexers FPGA Optimization For
Page 221 and 222: RAMs FPGA Optimization Two types of
Page 223 and 224: Flip-Flop Retiming FPGA Optimizatio
Page 225 and 226: FPGA Optimization INCREMENTAL_SYNTH
Page 227 and 228: FPGA Optimization Note In the curre
Page 229 and 230: FPGA Optimization generated NGC fil
Page 231 and 232: FPGA Optimization The problem most
Page 233 and 234: Log File Analysis FPGA Optimization
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Page 237 and 238: FPGA Optimization NOTE: THESE TIMIN
Page 239 and 240: FPGA Optimization The start point a
Page 241 and 242: FPGA Optimization If the box_type a
Page 243 and 244: Instantiation of MUXF5 FPGA Optimiz
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Page 251 and 252: PCI Flow FPGA Optimization To succe
Page 253 and 254: CPLD Optimization This chapter cont
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Page 257 and 258: CPLD Optimization • Final results
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CPLD Optimization The CPLD fitter m
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Design Constraints Chapter 5 This c
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Synthesis Options Design Constraint
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Design Constraints Figure 5-4 Synth
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• Mux Extraction • Mux Style
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Design Constraints For FPGA device
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XST Constraint File (XCF) Design Co
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Design Constraints Timing Constrain
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Design Constraints • Add IO Buffe
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Design Constraints the components c
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HDL Constraints Design Constraints
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FPGA Constraints (non-timing) Desig
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Design Constraints • Number of Cl
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Design Constraints This constraint
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Timing Constraints Design Constrain
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Design Constraints See the “CLOCK
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Design Constraints The following ti
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Design Constraints • TIMEGRP TIME
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Design Constraints See the “INPAD
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Constraint Name clock_buffer bufgdl
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Constraint Name move_last- _stage m
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Constraint Name xor_collapse yes, n
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Constraint Name synthesis/ synopsis
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Design Constraints The following ta
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*Also Supported in XCF format. Impl
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Design Constraints The binary equiv
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Table 5-5 Third Party Constraints N
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Table 5-5 Third Party Constraints N
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Constraints Precedence Design Const
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VHDL Language Support Chapter 6 Thi
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VHDL Language Support 'W' means wea
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VHDL Language Support compiled in t
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Record Types Objects in VHDL MATRIX
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Entity Declaration VHDL Language Su
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VHDL Language Support Example 6-2 g
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VHDL Language Support Example 6-3 4
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egin Y 13), port map (X,Y,C1); C2
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VHDL Language Support Example 6-5 M
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VHDL Language Support Example 6-8 N
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Example 6-10 Combinatorial Process
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VHDL Language Support Example 6-12
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For...Loop Statement VHDL Language
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Sequential Process without a Sensit
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egin if RST = '1' then DO
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Multiple Wait Statements Descriptio
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Functions and Procedures VHDL Langu
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VHDL Language Support Example 6-24
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STANDARD Package VHDL Language Supp
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VHDL Language Support Note Function
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Packages Enumeration Types Integer
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Table 6-4 Objects VHDL Language Sup
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Wait Statement Loop Statement Table
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VHDL Reserved Words The following t
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Verilog Language Support Chapter 7
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Behavioral Verilog Features Verilog
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Verilog Language Support Example 7-
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Table 7-1 Expressions Bitwise Negat
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Modules Verilog Language Support In
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Procedural Assignments Verilog Lang
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Verilog Language Support Casez trea
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While Loops Verilog Language Suppor
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Verilog Language Support Example 7-
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Verilog Language Support The main l
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Verilog Language Support • You ca
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Example 7-9 Function Declaration an
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Blocking Versus Non-Blocking Proced
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Include Files Verilog Language Supp
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Verilog Language Support Each insta
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Parameters Verilog Language Support
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Verilog Language Support • Design
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Verilog Meta Comments Verilog Langu
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Table 7-4 Data Types Registers Vect
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Table 7-8 Design Hierarchy Module d
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Verilog Reserved Keywords Verilog L
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Command Line Mode Introduction Chap
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Command Line Mode • Script File
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Command Line Mode • Second column
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Table 8-4 HDL Options (VHDL and Ver
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Command Line Mode Table 8-6 Target
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Command Line Mode • To get a list
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Elaborate Command Time Command Comm
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♦ smallcntr.vhd Command Line Mode
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Command Line Mode You can improve t
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Command Line Mode Sometimes, XST is
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XST Shell Command Line Mode To use
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Case 2 Command Line Mode Each desig
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Log File Analysis Introduction This
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Quiet Mode Timing Report Log File A
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RAM Style : Auto ROM Extraction : y
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Synthesizing Unit . Related source
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# Counters : 2 # 4-bit up counter :
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Log File Analysis Data Path: sixty_
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CPLD Log File Log File Analysis The
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Analyzing Entity (Architecture ).
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Log File Analysis =================
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XST Naming Conventions This appendi
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