HC210 datasheet(149/228 Pages) ALTERA

149 / 228 page

Altera Corporation

6–21

September 2008

Assigning Timing Constraints

The minimum set of timing constraints for a HardCopy II design are:

■

Clock settings (FMAX) for each and every clock domain

■

Minimum and maximum delays for all I/O paths, including

asynchronous reset and control I/O signals

In addition, it is good design practice to develop timing constraints to

cover:

■

Specific cross-clock domain timing requirements

■

False paths

■

Multicycle paths

In TimeQuest, timing constraints are written in TimeQuest SDC format

and are read from an SDC file. An example file is demo_design.sdc. See

“Using TimeQuest” on page 6–30.

In the Classic Timing Analyzer, timing constraints are applied using

dedicated Tcl commands and by assigning timing-specific attributes

using the

set_instance_assignment command.

This section provides an overview of timing constraint development

using Tcl commands.

For more information on timing constraints, refer to the Timing Analysis

section in volume 3 of the Quartus II Handbook.

Specifying System Clocks

The most basic constraints that should be applied describe the clock for

each clock domain. Parameters usually specified for each clock are:

■

Clock period

■

Latency (

LATE_CLOCK_LATENCY/EARLY_CLOCK_LATENCY

assignments)

■

Uncertainty (

set_clock_uncertainty command)

Clock uncertainty specified with the

set_clock_uncertainty

command models any uncertainty in the clock period, including jitter,

and is often used to introduce some margin into the target clock

frequency. The following example constraints illustrate clock definition

for a design with two clock domains,

clk_a and clk_b. In this case, both

clocks run at 100 MHz, but with different clock latency and skew.

## Example TimeQuest SDC Constraints Defining Clocks clk_a and clk_b

create_clock -period 10.0 -name clk_a [get_ports clk_a]

set_clock_latency -source -late 3.0 clk_a

set_clock_latency -source -early 2.0 clk_a

HC210 Datasheet(PDF) 149 Page - Altera Corporation

HC210 Datasheet(HTML) 149 Page - Altera Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL