Scripting

set_false_path


The following table displays information for the set_false_path Tcl command:

Tcl Package and Version

Belongs to ::quartus::sdc 1.5

Syntax

set_false_path [-h | -help] [-long_help] [-fall_from <names>] [-fall_to <names>] [-from <names>] [-hold] [-rise_from <names>] [-rise_to <names>] [-setup] [-through <names>] [-to <names>]

Arguments

-h | -help

Short help

-long_help

Long help with examples and possible return values

-fall_from <names>

Valid source clocks (string patterns are matched using Tcl string matching)

-fall_to <names>

Valid destination clocks (string patterns are matched using Tcl string matching)

-from <names>

Valid sources (string patterns are matched using Tcl string matching)

-hold

Specifies the false_path value (applies only to clock hold or removal checks)

-rise_from <names>

Valid source clocks (string patterns are matched using Tcl string matching)

-rise_to <names>

Valid destination clocks (string patterns are matched using Tcl string matching)

-setup

Specifies the false_path value (applies only to clock setup or recovery checks)

-through <names>

Valid through nodes (string patterns are matched using Tcl string matching)

-to <names>

Valid destinations (string patterns are matched using Tcl string matching)

Description

Specifies a false-path exception, removing (or cutting) paths from
timing analysis.

The -from and -to values are collections of clocks, registers, ports,
pins, or cells in the design.  If the -from or -to values are not
specified, the collection is converted automatically into [get_keepers
*].  It is worth noting that if the counterpart of the unspecified
collection is a clock collection, it is more efficient to explicitly
specify this collection as a clock collection only if the clock
collection also generates the desired assignment.

Applying exceptions between clocks applies the exception from all
register or ports driven by the -from clock to all registers or ports
driven by the -to clock. Applying exceptions between a pair of clocks
is more efficient than for specific node to node or node to clock
paths.

If pin names or collections are used, the -from value must be a clock
pin and the -to value must be any non-clock input pin to a
register. Assignments from clock pins or to and from cells applies to
all registers in the cell or driven by the clock pin.

The -through values are collections of pins or nets in the design. An
exception applied through a node in the design applies only to paths
through the specified node.

The -rise_from and -fall_from options can be used in place of the
-from destination nodes. The rise or fall value of the option
indicates that the "from" nodes are driven by the rising or falling
edge of the clock that feeds this node, taking into consideration any
logical inversions along the clock path.  The -from option is the
combination of both rising and falling "from" nodes.  If the "from"
collection is a clock collection, the assignment applies to those
nodes that are driven by the respective rising or falling clock edge.

The -rise_to and -fall_to options behave similarly to the "from"
options described previously. These assignments restrict the given
assignment to only those nodes or clocks that correspond to the
specified rise or fall value, taking into consideration any logical
inversions that are along the clock path.

The -setup and -hold options allow the false path to only be applied
to the corresponding setup/recovery or hold/removal checks. The
default if neither value is specified is to apply the false path to
both -setup and -hold.

The values of the -from, -to, -through, and other similar options are
either collections or a Tcl list of wildcards used to create
collections of appropriate types. The values used must follow standard
Tcl or TimeQuest-extension substitution rules.  See help for the
use_timequest_style_escaping command for details.

See help for the set_clock_groups command for information.

Example Usage

# Set a false-path between two unrelated clocks
# See also set_clock_groups
set_false_path -from [get_clocks clkA] -to [get_clocks clkB]

# Set a false-path for a specific path
set_false_path -from [get_pins regA|clk] -to [get_pins regB|aclr]

# Set a false-path from a node to a falling clock
set_false_path -from [get_pins regA|clk] -fall_to [get_clocks clkB]

Return Value

Code Name

Code

String Return

TCL_OK 0 INFO: Operation successful