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Xilinx Synthesis Technology User Guide

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XST <strong>User</strong> <strong>Guide</strong><br />

Verilog .................................................................................2-172<br />

State Machines .............................................................................2-172<br />

Related Constraints .................................................................2-174<br />

FSM with 1 Process .................................................................2-175<br />

VHDL ..................................................................................2-175<br />

Verilog .................................................................................2-176<br />

FSM with 2 Processes .............................................................2-177<br />

VHDL ..................................................................................2-178<br />

Verilog .................................................................................2-179<br />

FSM with 3 Processes .............................................................2-180<br />

VHDL ..................................................................................2-180<br />

Verilog .................................................................................2-182<br />

State Registers ........................................................................2-183<br />

Next State Equations ...............................................................2-183<br />

FSM Outputs ............................................................................2-183<br />

FSM Inputs ...............................................................................2-184<br />

State Encoding Techniques .....................................................2-184<br />

Auto ....................................................................................2-184<br />

One-Hot ..............................................................................2-184<br />

Gray ....................................................................................2-184<br />

Compact .............................................................................2-185<br />

Johnson ..............................................................................2-185<br />

Sequential ...........................................................................2-185<br />

<strong>User</strong> ....................................................................................2-185<br />

Log File ....................................................................................2-186<br />

Black Box Support .........................................................................2-187<br />

Log File ....................................................................................2-187<br />

Related Constraints .................................................................2-187<br />

VHDL .......................................................................................2-188<br />

Verilog ......................................................................................2-189<br />

Chapter 3 FPGA Optimization<br />

Introduction ...................................................................................3-1<br />

Virtex Specific <strong>Synthesis</strong> Options .................................................3-2<br />

Macro Generation .........................................................................3-3<br />

Arithmetic Functions ................................................................3-4<br />

Loadable Functions ..................................................................3-4<br />

Multiplexers ..............................................................................3-5<br />

Priority Encoder .......................................................................3-5<br />

Decoder ...................................................................................3-6<br />

Shift Register ...........................................................................3-6<br />

RAMs .......................................................................................3-7<br />

ROMs .......................................................................................3-8<br />

Flip-Flop Retiming .........................................................................3-9<br />

Incremental <strong>Synthesis</strong> Flow. .........................................................3-10<br />

INCREMENTAL_SYNTHESIS: ................................................3-10<br />

Example ..............................................................................3-11<br />

RESYNTHESIZE .....................................................................3-12<br />

VHDL Flow .........................................................................3-12<br />

xiv <strong>Xilinx</strong> Development System

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