Xilinx Constraints Guide

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Chapter 4: Xilinx Constraints COOL_CLK (CoolCLOCK) Architecture Support Applicable Elements Propagation Rules COOL_CLK (CoolCLOCK) reduces clocking power within a CPLD device by combining clock division circuitry with the DualEDGE circuitry. Because the clock net can be a significant power drain, the clock power can be reduced by driving the net at half frequency, then doubling the clock rate using DualEDGE triggered macrocells. Applies to CoolRunner-II devices only. Applies to any input pad or internal signal driving a register clock. Applying COOL_CLK to a clock net is equivalent to passing the clock through a divide-by-two clock divider (CLK_DIV2) and replacing all flip-flops controlled by that clock with DualEDGE flip-flops. Using COOL_CLK does not alter your overall design functionality. Some restrictions apply: • You cannot use COOL_CLK on a clock that triggers any flip-flop on the low-going edge. The CoolRunner-II clock divider can be triggered only on the high-rising edge of the clock signal. • If there are any DualEDGE flip-flops in your design source, the clock that controls any of them cannot be specified as a COOL_CLK. • If there is already a clock divider in your design source, you cannot also use COOL_CLK. CoolRunner-II devices contain only one clock divider. Syntax Examples The following examples show how to use this constraint with particular tools or methods. If a tool or method is not listed, you cannot use this constraint with it. Schematic Syntax • Attach to a input pad or internal signal driving a register clock • Attribute Name COOL_CLK • Attribute Values – TRUE – FALSE VHDL Syntax Declare the VHDL constraint as follows: attribute cool_clk: string; Specify the VHDL constraint as follows: attribute cool_clk of signal_name: signal is “{TRUE | FALSE}”; For more information about basic VHDL syntax, see VHDL Attributes. Constraints Guide 88 www.xilinx.com UG625 (v. 13.2) July 6, 2011
Verilog Syntax Chapter 4: Xilinx Constraints Place the Verilog constraint immediately before the module or instantiation. Specify the Verilog constraint as follows: (* COOL_CLK = “{TRUE | FALSE}” *) For more information about basic Verilog syntax, see Verilog Attributes. UCF and NCF Syntax NET “signal_name” COOL_CLK; Constraints Guide UG625 (v. 13.2) July 6, 2011 www.xilinx.com 89
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Constraints Guide UG625 (v. 13.2) J
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Table of Contents Revision History
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IBUF_DELAY_VALUE (Input Buffer Dela
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Constraint Types Attributes and Con
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Grouping Constraints for Timing Cha
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The name qualifier can include the
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Physical Constraints Mapping Note T
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Placement Constraints Chapter 1: Co
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Routing Directives Routing directiv
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Timing Constraints Chapter 1: Const
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UCF Timing Constraint Support From-
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Timing Model Constraint Priority Ch
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Chapter 2 Entry Strategies for Xili
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Constraint Schematic VHDL Verilog L
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An attribute can be declared in an
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User Constraints File (UCF) UCF Flo
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Syntax Chapter 2: Entry Strategies
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Entering Multiple Constraints File
Page 37 and 38: Chapter 2: Entry Strategies for Xil
Page 39 and 40: Running Constraints Editor As a Sta
Page 41 and 42: Defining I/O Pin Configurations Cha
Page 43 and 44: Placement LOC Constraint Assignment
Page 45 and 46: Verilog Example -------------module
Page 47 and 48: Chapter 2: Entry Strategies for Xil
Page 49 and 50: Timing Specification Priorities Cha
Page 51 and 52: Timing Constraint Strategies Chapte
Page 53 and 54: Chapter 3: Timing Constraint Strate
Page 55 and 56: The global OFFSET IN constraint for
Page 57 and 58: The PERIOD constraint syntax for th
Page 59 and 60: Example Chapter 3: Timing Constrain
Page 61 and 62: Chapter 3: Timing Constraint Strate
Page 63 and 64: The global OFFSET OUT constraints f
Page 65 and 66: Multi-Cycle Paths Chapter 3: Timing
Page 67 and 68: Xilinx Constraints Each Xilinx® co
Page 69 and 70: RANGE Chapter 4: Xilinx Constraints
Page 71 and 72: Chapter 4: Xilinx Constraints Range
Page 73 and 74: COMPRESSION GROUP PLACE Chapter 4:
Page 75 and 76: Defining From Timing Groups Chapter
Page 77 and 78: BEL (BEL) The BEL (BEL) constraint:
Page 79 and 80: BLKNM (Block Name) Architecture Sup
Page 81 and 82: BUFG (BUFG) The BUFG (BUFG) constra
Page 83 and 84: Clock Dedicated Route (CLOCK_DEDICA
Page 85 and 86: COMPGRP (Component Group) Architect
Page 87: • S_SELECTMAP16 Slave SelectMAP M
Page 91 and 92: Verilog Syntax Chapter 4: Xilinx Co
Page 93 and 94: PCF Syntax CONFIG DCI_CASCADE = ",
Page 95 and 96: Default (DEFAULT) Chapter 4: Xilinx
Page 97 and 98: Example (* KEEPER = “TRUE” *) D
Page 99 and 100: DIFF_TERM (Diff_Term) Architecture
Page 101 and 102: DIRECTED_ROUTING (Directed Routing)
Page 103 and 104: DISABLE (Disable) The DISABLE (Disa
Page 105 and 106: DRIVE (Drive) The DRIVE (Drive) con
Page 107 and 108: XCF Syntax MODEL “entity_name”
Page 109 and 110: ENABLE (Enable) The ENABLE (Enable)
Page 111 and 112: ENABLE_SUSPEND (Enable Suspend) Arc
Page 113 and 114: Verilog Syntax Chapter 4: Xilinx Co
Page 115 and 116: Constraints Editor Syntax Chapter 4
Page 117 and 118: VHDL Syntax Declare the VHDL constr
Page 119 and 120: UCF and NCF Syntax NET “signal_na
Page 121 and 122: Chapter 4: Xilinx Constraints You a
Page 123 and 124: Constraints Editor Syntax Chapter 4
Page 125 and 126: HBLKNM (Hierarchical Block Name) Ar
Page 127 and 128: HIODELAY_GROUP (HIODELAY Group) Arc
Page 129 and 130: VHDL Syntax Declare the VHDL constr
Page 131 and 132: HU_SET (HU Set) The HU_SET (HU Set)
Page 133 and 134: IBUF_DELAY_VALUE (Input Buffer Dela
Page 135 and 136: IFD_DELAY_VALUE (IFD Delay Value) T
Page 137 and 138: IN_TERM (In Term) Architecture Supp
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INREG (Input Registers) Architectur
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IOB (IOB) The IOB constraint: • I
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IOBDELAY (Input Output Block Delay)
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IODELAY_GROUP (IODELAY Group) Limit
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IOSTANDARD (Input Output Standard)
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Pinout and Area Constraints Editor
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Verilog Syntax Chapter 4: Xilinx Co
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Architecture Support Applicable Ele
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Keeper (KEEPER) Architecture Suppor
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LOC (Location) The LOC (Location) c
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Chapter 4: Xilinx Constraints The w
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LOC Range Constraint Examples Const
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PlanAhead Syntax Chapter 4: Xilinx
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Schematic LOC=P17 Chapter 4: Xilinx
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Example One Chapter 4: Xilinx Const
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Slices Prohibited Example Two Chapt
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LOCK_PINS (Lock Pins) Architecture
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where value is any chosen name unde
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MAP (Map) Architecture Support Appl
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Specify the Verilog constraint as f
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Architecture Support Applicable Ele
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MAXDELAY (Maximum Delay) Architectu
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PCF Syntax item MAXDELAY = maxvalue
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MAXSKEW (Maximum Skew) The MAXSKEW
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FPGA Editor Syntax Chapter 4: Xilin
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MIODELAY_GROUP (MIODELAY Group) Arc
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VHDL Syntax Declare the VHDL constr
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UCF and NCF Syntax Chapter 4: Xilin
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where Chapter 4: Xilinx Constraints
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Falling Edge Constraints Chapter 4:
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PlanAhead Syntax Chapter 4: Xilinx
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where Chapter 4: Xilinx Constraints
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UCF Syntax NET “clock” TNM_NET
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Attribute OUT_TERM: string; Specify
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TIMESPEC PERIOD Method Chapter 4: X
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Examples of a Primary Clock with De
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where • period is the required cl
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New PERIOD Specifications Output Pi
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Post CRC (POST_CRC) Architecture Su
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Post CRC Frequency (POST_CRC_FREQ)
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Post CRC Signal (POST_CRC_SIGNAL) A
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PRIORITY (Priority) Architecture Su
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The following are not supported: Ch
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PULLDOWN (Pulldown) Architecture Su
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PULLUP (Pullup) Architecture Suppor
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PWR_MODE (Power Mode) Architecture
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REG (Registers) The REG (Registers)
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RLOC (Relative Location) The Relati
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RLOC = X3Y4 Chapter 4: Xilinx Const
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Linking Sets Set Linkage Chapter 4:
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Chapter 4: Xilinx Constraints by th
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Linking Two HU_SET Sets Chapter 4:
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Specify the VHDL constraint as foll
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Chapter 4: Xilinx Constraints Diffe
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H_SET (H Set) Chapter 4: Xilinx Con
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Chapter 4: Xilinx Constraints The n
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Syntax Examples Chapter 4: Xilinx C
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RLOC_RANGE (Relative Location Range
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where the relative X values (m1 and
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UCF and NCF Syntax NET “mysignal
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VHDL Syntax Chapter 4: Xilinx Const
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SLOW (Slow) The SLOW (Slow) constra
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STEPPING (Stepping) Architecture Su
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VHDL Syntax Chapter 4: Xilinx Const
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Constraints Editor Syntax Chapter 4
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Chapter 4: Xilinx Constraints The f
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TIMEGRP (Timing Group) The TIMEGRP
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Defining Latch Subgroups by Gate Se
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Chapter 4: Xilinx Constraints When
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PCF Syntax TIMEGRP name; TIMEGRP na
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Separators FROM-TO Syntax TIMESPEC
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TNM (Timing Name) Chapter 4: Xilinx
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Chapter 4: Xilinx Constraints A qua
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TNM_NET (Timing Name Net) The TNM_N
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Schematic Syntax • Attach to a ne
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TPSYNC (Timing Point Synchronizatio
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UCF and NCF Syntax NET “net_name
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Using TPTHRU in a FROM TO Constrain
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TSidentifier (Timing Specification
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Ignoring Paths Note This form is no
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Chapter 4: Xilinx Constraints If yo
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Use Low Skew Lines (USELOWSKEWLINES
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VCCAUX (VCCAUX) Architecture Suppor
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VREF (VREF) The VREF (VREF) constra
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XBLKNM (XBLKNM) Architecture Suppor
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Additional Resources Appendix • X
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Xilinx Constraints Guide

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