set_max_skew (::quartus::sdc

Tcl Package and Version

Syntax

set_max_skew [-h | -help] [-long_help] [-fall_from_clock <names> ] [-fall_to_clock <names> ] [-from <names> ] [-from_clock <names> ] [-get_skew_value_from_clock_period <src_clock_period|dst_clock_period|min_clock_period> ] [-rise_from_clock <names> ] [-rise_to_clock <names> ] [-skew_value_multiplier <multiplier> ] [-to <names> ] [-to_clock <names> ] [ <skew> ]

Arguments

-h | -help

Short help

-long_help

Long help with examples and possible return values

-fall_from_clock <names>

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

-fall_to_clock <names>

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

-from <names>

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

-from_clock <names>

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

-get_skew_value_from_clock_period <src_clock_period|dst_clock_period|min_clock_period>

Compute skew constraint as a multiple of the clock period

-rise_from_clock <names>

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

-rise_to_clock <names>

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

-skew_value_multiplier <multiplier>

Value by which the clock period should be multiplied to compute skew requirement

-to <names>

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

-to_clock <names>

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

<skew>

Required skew

Description

Use the set_max_skew constraint to perform maximum
allowable skew analysis between sets of registers or
ports. In order to constrain skew across multiple
paths, all such paths must be defined within a single
set_max_skew constraint. The set_max_skew timing
constraint is not affected by the set_max_delay,
set_min_delay, set_multicycle_path, and set_false_path constraints
but is affected by the set_clock_groups -exclusive
constraint. Paths between exclusive clocks are not
analyzed for skew, and no two paths are compared for
skew if their clocks are exclusive to each other.
However, paths whose clocks are asynchronous are
still analyzed for skew.

Legal values for the -from and -to options are
collections of clocks, registers, ports, pins,
cells or partitions in a design.

Applying maximum skew constraints between clocks
applies the constraint from all register or ports
driven by the clock specified with the -from option to
all registers or ports driven by the clock specified
with the -to option.

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 apply to all registers
contained in the cell or driven by the clock pin.
Similarly, -to and -from partition specifications
apply to all registers in the specified partition.

Max skew analysis includes data arrival times, clock arrival times, 
register micro parameters, clock uncertainty, on-die variation and 
ccpp removal. 

Use -get_skew_value_from_clock_period to set the skew 
requirement to be equal to the launching or latching clock 
period, or whichever of the two has a smaller period.
If -skew_value_multiplier is used, the requirement is multiplied
by that value.  If this option is used, then the positional 
skew option may not be set.  If the set of skew paths is 
clocked by more than one clock, the Timing Analyzer will use the 
one with smallest period to compute the skew constraint.

When this constraint is used, results of max skew
analysis are displayed in the Report Max Skew
(report_max_skew) report from the Timing Analyzer.
Since skew is defined between two or more paths, no
results are displayed if the -from/-from_clock and
-to/-to_clock filters satisfy less than two paths.

Example Usage

# Constrain the skew on an input port to all registers it feeds
set_max_skew -from [get_ports din] 0.200

# Constrain the skew on output bus dout[*]
set_max_skew -to [get_ports dout\[*\]] 0.200

# Constrain skew to be less than 90% of the period of any clock  in the source
# register set
set_max_skew -to [get_keepers inst1|*] -get_skew_value_from_clock_period src_clock_period -skew_value_multiplier 0.900

# Report the results of max skew assignments
report_max_skew -panel_name "Report Max Skew" -npaths 10 -detail path_only

Return Value

Code Name

Code

String Return

TCL_OK

0

INFO: Operation successful

TCL_ERROR

1

ERROR: Timing netlist does not exist. Use create_timing_netlist to create a timing netlist.

TCL_ERROR

1

ERROR: <string> is not a valid argument for option -exclude. Available argument is to_clock

Tcl Package and Version	Belongs to ::quartus::sdc_ext 2.0
Syntax	`set_max_skew [-h \| -help] [-long_help]` `[-fall_from_clock` <names> `]` `[-fall_to_clock` <names> `]` `[-from` <names> `]` `[-from_clock` <names> `]` `[-get_skew_value_from_clock_period` <src_clock_period\|dst_clock_period\|min_clock_period> `]` `[-rise_from_clock` <names> `]` `[-rise_to_clock` <names> `]` `[-skew_value_multiplier` <multiplier> `]` `[-to` <names> `]` `[-to_clock` <names> `]` `[` <skew> `]`
Arguments	`-h \| -help`		Short help
	`-long_help`		Long help with examples and possible return values
	`-fall_from_clock` <names>		Valid source clocks (string patterns are matched using Tcl string matching)
	`-fall_to_clock` <names>		Valid destination clocks (string patterns are matched using Tcl string matching)
	`-from` <names>		Valid sources (string patterns are matched using Tcl string matching)
	`-from_clock` <names>		Valid source clocks (string patterns are matched using Tcl string matching)
	`-get_skew_value_from_clock_period` <src_clock_period\|dst_clock_period\|min_clock_period>		Compute skew constraint as a multiple of the clock period
	`-rise_from_clock` <names>		Valid source clocks (string patterns are matched using Tcl string matching)
	`-rise_to_clock` <names>		Valid destination clocks (string patterns are matched using Tcl string matching)
	`-skew_value_multiplier` <multiplier>		Value by which the clock period should be multiplied to compute skew requirement
	`-to` <names>		Valid destinations (string patterns are matched using Tcl string matching)
	`-to_clock` <names>		Valid destination clocks (string patterns are matched using Tcl string matching)
	<skew>		Required skew
Description	Use the set_max_skew constraint to perform maximum allowable skew analysis between sets of registers or ports. In order to constrain skew across multiple paths, all such paths must be defined within a single set_max_skew constraint. The set_max_skew timing constraint is not affected by the set_max_delay, set_min_delay, set_multicycle_path, and set_false_path constraints but is affected by the set_clock_groups -exclusive constraint. Paths between exclusive clocks are not analyzed for skew, and no two paths are compared for skew if their clocks are exclusive to each other. However, paths whose clocks are asynchronous are still analyzed for skew. Legal values for the -from and -to options are collections of clocks, registers, ports, pins, cells or partitions in a design. Applying maximum skew constraints between clocks applies the constraint from all register or ports driven by the clock specified with the -from option to all registers or ports driven by the clock specified with the -to option. 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 apply to all registers contained in the cell or driven by the clock pin. Similarly, -to and -from partition specifications apply to all registers in the specified partition. Max skew analysis includes data arrival times, clock arrival times, register micro parameters, clock uncertainty, on-die variation and ccpp removal. Use -get_skew_value_from_clock_period to set the skew requirement to be equal to the launching or latching clock period, or whichever of the two has a smaller period. If -skew_value_multiplier is used, the requirement is multiplied by that value. If this option is used, then the positional skew option may not be set. If the set of skew paths is clocked by more than one clock, the Timing Analyzer will use the one with smallest period to compute the skew constraint. When this constraint is used, results of max skew analysis are displayed in the Report Max Skew (report_max_skew) report from the Timing Analyzer. Since skew is defined between two or more paths, no results are displayed if the -from/-from_clock and -to/-to_clock filters satisfy less than two paths.
Example Usage	# Constrain the skew on an input port to all registers it feeds set_max_skew -from [get_ports din] 0.200 # Constrain the skew on output bus dout[] set_max_skew -to [get_ports dout\[\]] 0.200 # Constrain skew to be less than 90% of the period of any clock in the source # register set set_max_skew -to [get_keepers inst1\|*] -get_skew_value_from_clock_period src_clock_period -skew_value_multiplier 0.900 # Report the results of max skew assignments report_max_skew -panel_name "Report Max Skew" -npaths 10 -detail path_only
Return Value	Code Name	Code	String Return
	TCL_OK	0	INFO: Operation successful
	TCL_ERROR	1	ERROR: Timing netlist does not exist. Use create_timing_netlist to create a timing netlist.
	TCL_ERROR	1	ERROR: <string> is not a valid argument for option -exclude. Available argument is to_clock

set_max_skew (::quartus::sdc_ext)