.. _set_resource_constraint:

set_resource_constraint
-----------------------

This Tcl command constrains the resource allocated by LegUp.
For instance, to only have a single divider in the entire circuit, user can specify: ``set_resource_constraint divide 1``.
This makes LegUp instantiate a maximum of 1 divider in the circuit, and if there are multiple division operations required, they will share the same divider. 
 
Note: A constraint on "divide" will apply to:
  - signed_divide_8
  - signed_divide_16
  - signed_divide_32
  - signed_divide_64
  - unsigned_divide_8
  - unsigned_divide_16
  - unsigned_divide_32
  - unsigned_divide_64

It can also be used to constrain the number of memory ports. To make all memories single-ported: ``set_resource_constraint memory_port 1``
For memory ports, only 1 and 2 are valid values, as FPGA RAMs have up to 2 ports. 

This Tcl command should only be used by advanced LegUp users. 

**Category**

HLS Constraints

**Value Type**

set_resource_constraint <operation> <constraint>
<operation> is a string 
<constraint> is an integer 

**Valid Values**

See Default and Examples
Note: operator name should match the device family operation database file:
boards/PolarFire/PolarFire.tcl

**Default Values**

::

    memory_port 2
    divide 1
    modulus 1
    multiply 2
    fp_add 1
    fp_subtract 1
    fp_multiply 1
    fp_divide 1
    fp 1

**Location Where Default is Specified**

``examples/legup.tcl``

**Dependencies**

None

**Applicable Flows**

All devices and flows

**Test Status**

Actively in-use

**Examples**

``set_resource_constraint signed_divide_16 3``

``set_resource_constraint signed_divide 2``

``set_resource_constraint divide 1``

.. NOTE::
  When implementing an integer multiply operation, LegUp's default behaviour is
  to optimize for timing (Fmax) by mapping a multiply operation to target DSPs.
  When a multiply operation is wider than the DSP can support, LegUp splits the
  multiply into multiple DSPs and automatically inserts registers to help RTL
  synthesis tool to utilize registers in DSPs better, and hence achieve better
  timing.

  However, this split-multiply feature cannot support sharing multipliers.
  When ``set_resource_constraint multiply X`` is specified by user, LegUp will
  turn off the split-multiply feature and use a generic multiplier that can be
  shared by more than one multiply operations.
  LegUp will also print a warnign as follows,
  *Warning: Detected set_resource_constraint setting for integer multiplier.  However, multiplier sharing is incompatible with the multiply splitting feature.  Disabling multiply splitting feature and the normal multiplier modules will be used.*

  Similarly, ``set_operation_latency multiply X`` will trigger the same
  behaviour because the split-multiply does not support user-configured
  multiply latency.

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