.. _CLOCK_PERIOD:

CLOCK_PERIOD
-------------

This is a widely used constraint that allows the user to set the
target clock period for a design.  The clock period is specified in
nanoseconds.

It has a significant impact on scheduling: the scheduler will schedule
operators into clock cycles using delay estimates for each operator,
such that the specified clock period is honored.  In other words,
operators will be chained together combinationally to the extent
allowed by the value of the CLOCK_PERIOD parameter.

LegUp has a default CLOCK_PERIOD value for each device family that is
supported. 

.. That default value was chosen to minimize the wall-clock
    time for a basket of benchmark programs (mainly the CHStone benchmark
    circuits).

    If the parameter SDC_NO_CHAINING is 1, then the CLOCK_PERIOD parameter
    has no effect.

**Category**

HLS Constraints

**Value Type**

Integer represent a value in nanoseconds

**Valid Values**

Integer

**Default Value**

Depends on the target device

.. **Location Where Default is Specified**
    For example:
    ``boards/PolarFire/PolarFire.tcl``

**Dependencies**

.. SDC_NO_CHAINING: If this parameter is set to 1, then CLOCK_PERIOD does
    nothing.

**Applicable Flows**

All devices and flows

**Test Status**

Actively in-use

**Examples**

    ``set_parameter CLOCK_PERIOD 15``

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