PrimeTime Commandsv1999.10

set_min_delay

Specifies minimum delay for timing paths.

SYNTAX

string set_min_delay [-rise] [-fall] [-reset_path] [-from from_list ] [-throughthrough_list ]* [-to to_list ] delay_valuelist from_listlist to_listfloat delay_value

ARGUMENTS

-riseSpecifies whether endpoint rising delays are constrained. If you do notspecify -rise or -fall , both rising and falling delays are constrained.

-fallSpecifies whether endpoint falling delays are constrained. If you do notspecify -rise or -fall , both rising and falling delays are constrained.

-reset_pathRemoves existing point-to-point exception information on the specified paths.If used with -to only, all paths leading to the specified endpoints are reset.If used with -from only, all paths leading from the specified startpoints arereset. If used with -from and -to , only paths between those points are reset.Only information of the same rise or fall setup or hold type is reset. Thisis equivalent to using the reset_path command with similar arguments beforethe set_min_delay command is issued.

-from from_listSpecifies a list of timing path startpoint objects. A valid timing startpointis a clock, a primary input or inout port, a sequential cell, a clock pin ofa sequential cell, a data pin of a level-sensitive latch, or a pin that hasinput delay specified. If a clock is specified, all registers and primaryinputs related to that clock are used as path startpoints. If you specify acell, one path startpoint on that cell is affected.

-through through_listLists the pins, ports, or nets through which the paths must pass for minimumdelay definition. One can specify -through more than once in one commandinvocation. Nets are interpreted to imply the leaf-level driver pins. If youomit -through , all timing paths specified using the -from and -to options areaffected.Many groups of through_list can be specified using multiple -through options.The objects specified within one -through option are assumed to be in OR mode.The group of objects specified with multiple -through options are assumed tobe in AND mode.If -through is specified once, PrimeTime applies minimum delay constraintonly for those paths that travel through one or more of the objects in thelist.If multiple -through are specified, PrimeTime applies minimum delay

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PrimeTime Commandsv1999.10

constraint only for those paths that travel through one or more of the objectsin each list.The value of environment variable timing_through_compatibility affects theway PrimeTime interprets -through options. The default setting of thisvariable is false , which implies that objects specified with one or more -through options are interpreted as described above (OR-AND or Product of Sumformat).When the variable timing_through_compatibility is set to true , PrimeTime doesnot allow specification of through objects using multiple -through switches.Moreover, objects specified within one -through option are assumed to be inAND mode.

-to to_listSpecifies a list of timing path endpoint objects. A valid timing endpoint isa clock, a primary output or inout port, a sequential cell, a data pin of asequential cell, or a pin that has output delay specified. If a clock isspecified, all registers and primary outputs related to that clock are usedas path endpoints. If you specify a cell, one path endpoint on that cell isaffected.

delay_valueShows the value of the desired minimum delay for paths between start and endpoints. Express delay_value in the same units that the technology libraryused during analysis. If a path startpoint is on a sequential device, clockskew is included in the computed delay. If a path startpoint has an inputexternal delay specified, that delay value is added to the path delay. If apath endpoint is on a sequential device, clock skew and library setup timeare included in the computed delay. If the endpoint has an output externaldelay specified, that delay is added into the path delay.

DESCRIPTION

The set_min_delay command specifies a minimum delay for timing paths. It is used intwo cases:

1. To set a target minimum delay for output ports in a combinational design.

2. To override the default single cycle timing for paths, where set_multicycle_pathis not sufficient.

The value of a min_rise_delay attribute cannot be greater than that of amax_rise_delay attribute for the same path (and similarly for fall attributes). Ifthis occurs, the old attribute is removed.

Individual minimum delay targets are automatically derived from clock waveforms andport input or output delays. For more information, refer to the create_clock ,set_input_delay , and set_output_delay command man pages.

The set_min_delay command is a point-to-point timing exception command; it overridesthe default single-cycle timing relationship for one or more timing paths. Otherpoint-to-point timing exception commands include set_multicycle_path , set_max_delay ,and set_false_path . A specific set_max_delay or set_min_delay command overrides ageneral set_multicycle_path or set_false_path command.

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PrimeTime Commandsv1999.10

The more general commands apply to more than one path; either -from or -to is used(but not both), or clocks are used in the specification. Within a given point-to-point exception command, the more specific command overrides the more general. Thefollowing lists commands from highest to lowest precedence (more specific to moregeneral):

1. set_min_delay -from pin -to pin 2. set_min_delay -from clock -to pin 3. set_min_delay -from pin -to clock 4. set_min_delay -from pin 5. set_min_delay -to pin 6. set_min_delay -from clock -to clock 7. set_min_delay -from clock 8. set_min_delay -to clock

To remove information set by set_min_delay , use the reset_path or reset_designcommand.

EXAMPLES

In the following example, the set_min_delay command requires that any delay path topin Y is greater than 12.5 time units.

pt_shell> set_min_delay 12.5 -to Y

The following command specifies that all paths from A1 and A2 to Z5 must be greaterthan 4.0 units.

pt_shell> set_min_delay 4.0 -from {A1 A2} -to Z5

The following example specifies that all timing paths from ff1/CP to ff2/D, whichpasses through one or more of {U1/Z U2/Z} and one or more of {U3/Z U4/C} must begreater than 3.0 units.

pt_shell> set_min_delay 3.0 -from ff1/CP -through {U1/Z U2/Z} -through {U3/Z U4/C} -to ff2/D

SEE ALSO

current_design (2), report_constraint (2), reset_design (2), set_input_delay (2),set_output_delay (2), reset_path (2), set_false_path (2), set_multicycle_path (2),set_max_delay (2), timing_through_compatibility (3).

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