Xilinx Constraints Guide

XBLKNM (XBLKNM)
Architecture Support
Applicable Elements
Propagation Rules
The XBLKNM (XBLKNM) constraint:
• Is an advanced mapping constraint.
• Assigns block names to qualifying primitives and logic elements.
Chapter 4: Xilinx Constraints
If the same XBLKNM attribute is assigned to more than one instance, the software
attempts to pack logic with the same block name into one or more slices. Conversely, two
symbols with different XBLKNM names are not mapped into the same block. Placing the
same XBLKNM constraints on instances that do not fit within one block creates an error.
Specifying identical XBLKNM attributes on FMAP symbols tells the software to group
the associated function generators into a single slice. Using XBLKNM, you can partition
a complete slice without constraining the slice to a physical location on the device.
Hierarchical paths are not prefixed to XBLKNM attributes, so XBLKNM attributes for
different slices must be unique throughout the entire design.
The BLKNM attribute allows any elements except those with a different BLKNM to be
mapped into the same physical component. XBLKNM, however, allows only elements
with the same XBLKNM to be mapped into the same physical component. Elements
without an XBLKNM cannot be not mapped into the same physical component as those
with an XBLKNM.
XBLKNM can also be used with block RAMs.
Applies to FPGA devices. Does not apply to CPLD devices.
For information about which design elements can be used with which device families,
see the Libraries Guides. For more information, see the device data sheet.
Applies to the design element to which it is attached.
Syntax Examples
The following examples show how to use this constraint with particular tools or
methods. If a tool or method is not listed, you cannot use this constraint with it.
Values
block_name is a valid block name for that type of symbol
Schematic Syntax
• Attach to a valid instance
• Attribute Name
XBLKNM
• Attribute Values
See Values section above.
VHDL Syntax
Declare the VHDL constraint as follows:
Constraints Guide
UG625 (v. 13.2) July 6, 2011 www.xilinx.com 323