Xilinx Constraints Guide

BLKNM (Block Name)
Architecture Support
Applicable Elements
The BLKNM (Block Name) constraint:
• Is an advanced mapping constraint
• Assigns block names to qualifying primitives and logic elements.
Chapter 4: Xilinx Constraints
If the same BLKNM constraint is assigned to more than one instance, the software
attempts to map them into the same block. Conversely, two symbols with different
BLKNM names are not mapped into the same block. Placing similar BLKNM constraints
on instances that do not fit within one block causes an error.
Specifying identical BLKNM constraints on FMAP tells the software to group the
associated function generators into a single SLICE. Using BLKNM, you can partition a
complete SLICE without constraining the SLICE to a physical location on the device.
BLKNM constraints, like LOC constraints, are specified from the design. Since
hierarchical paths are not prefixed to BLKNM constraints, BLKNM constraints for
different SLICEs must be unique throughout the entire design. For information on
attaching hierarchy to block names, see Hierarchical Block Name (HBLKNM).
BLKNM allows any elements except those with a different BLKNM to be mapped
into the same physical component. Elements without a BLKNM can be packed with
those that have a BLKNM. For information on allowing only elements with the same
XBLKNM to be mapped into the same physical component, see XBLKNM.
Applies to FPGA devices. Does not apply to CPLD devices.
This constraint may be used with an FPGA device in one or more of the following design
elements, or categories of design elements. Not all devices support all elements. To see
which design elements can be used with which devices, see the Libraries Guides. For
more information, see the device data sheet.
• Flip-flop and latch primitives
• Any I/O element or pad
• FMAP
• ROM primitives
• RAMS and RAMD primitives
• Carry logic primitives
• Block RAM
Propagation Rules
You can also attach BLKNM to the net connected to the pad component in a User
Constraints File (UCF) file. NGDBuild transfers the constraint from the net to the pad
instance in the NGD file so that it can be processed by the mapper. Use the following
syntax:
NET “net_name” BLKNM=property_value;
When attached to a design element, this constraint is propagated to all applicable
elements in the hierarchy within the design element.
Constraints Guide
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