DS-FND-BSX-PC Xilinx Inc, DS-FND-BSX-PC Datasheet - Page 277

• Manufacturer Part Number: DS-FND-BSX-PC
• Description: FOUNDATION BASE SYS W/SYN EXPRES
• Manufacturer: Xilinx Inc
• Type: Foundation Systemr

Specifications of DS-FND-BSX-PC

• For Use With/related Products: Xilinx Programmable Logic Devices
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 122-1185

Foundation Series 2.1i User Guide
Physical Constraints File (PCF)
nism for establishing or modifying logical design constraints without
requiring you to re-enter a schematic or synthesis tool.
The process of building the complete logical design representation
(NGD files) is the job of NGDBuild. In developing this complete
design database, NGDBuild annotates design constraints with those
it finds in a UCF file. If a UCF file exists with the same name as the
top-level netlist then it will automatically be read. Otherwise, you
must indicate a specific file for User Constraints in the Options dialog
box. The syntax for the UCF constraints file is explained (on a per-
constraint basis) in the “Timing Constraints” section.
Note: Versions prior to M1.2 required the -uc switch to identify a
User Constraint File that needed to be annotated to the design.
Versions M1.2 and later allow UCF file annotation to be performed by
default—if the UCF file has the same base name as the input.
(FPGA only) The layout tools work on the physical design, so the
PCF file is written in terms that these tools can readily interpret.
Layout and timing constraints are written in terms of the physical
design’s components (COMPs), fractions of COMPs (BELs), and
collections of COMPs (macros).
Because of this different design viewpoint, the PCF syntax is not
necessarily the same as that used in the logical design constraint files
(UCF/NCF). Furthermore, because the PCF file is written for the
physical design implementation tools, its syntax may not be as
intuitive as the UCF file. Regardless of the syntactical challenges
associated with using a PCF file, many designers will choose to work
at the physical level of design abstraction for the following reasons.
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It is readily modified and immediately applicable to the present
task —implementing an FPGA (that is, there is no need to re-run
NGDBuild or MAP in order to run layout or analysis tools).
The implications of logical design structures on the physical
design’s implementation only become obvious once the design is
evaluated using the physical tools. Altering the PCF file for
“what-if” analysis can be desirable.
Certain constraints are only available within the PCF file.
Foundation Constraints
B-5