Implementation Tools: Glossary

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backannotation

The process of creating timing simulation netlists. ngdanno takes a mapped, placed, or routed NCD file and creates an NGD type file. ngdanno uses the NGM file to re-insert all of optimized logic and netnames into the NGD file so that the original functional testbench can be used for simulation. ngd2edif, ndg2xnf, ngd2vhdl, or ngd2ver can then convert the NGD type file to an EDIF or XNF netlist that can be accepted by a simulator.

Backannotation is executed by the Flow Engine GUI during the timing process. By default, backannotation is turned off in the Flow Engine. To enable backannotation in the Flow Engine, from the menu select Setup->Options, and in the options dialog

select Produce Timing Simulation Data. In the options dialog also click on the Edit Template button for Implementation and in the template dialog, select the Interface tab. On the Interface tab select the simulation netlist format: EDIF, XNF, VHDL, or Verilog, and select Correlate Simulation Data so all of the optimized netnames and logic are inserted into the simulation netlist.

BEL (Basic ELement)

An object in an NCD file that refers to either a LUT, flip flop, latch, or carry logic element.

BELs accumulate to form COMPs.

If a COMP is edited in EPIC, all of the internal BEL's are transformed into a SuperBEL.

BIT

A binary configuration file that represents a placed and routed FPGA design. A BIT file can be downloaded directly to an FPGA using the Hardware Debugger and XChecker cable. A BIT file can also be used as an input to the Prom File Formatter or promgen, which create configuration PROMs.

bitgen

A command line executable that translates a placed and routed NCD file to a BIT file.

carry logic

Logic inside of a CLB that quickly performs arithmetic carry functions.

CLB (Configurable Logic Block)

A physically co-located grouping of LUT's, flip flops, and carry logic.

clock skew

The maximum delay between arrival times of a clock edge at clock pins of multiple flip flops.

configuration

The process of programming an FPGA. Configuration occurs during power up and can optionally occur if a reprogram has been initiated.

COMP

An object in an NCD file that refers to either a CLB or IOB.

cost based cleanup passes

A feature in the place and route tools that tries to minimize routing delays on a completely routed design by choosing routing that has smaller cost values.

cost table

Each value (1 - 100) in the table initializes the placement algorithms to a different starting state. Because the algorithms start in a different state, the final results will be in a different state. By running multiple place and routes with different cost table entries, some of the runs will give improved results. On the command line, select a cost table entry by using the -t <number> option with par. Through the Design Manager, select a version and from the menu select Design->FPGA Multi-Pass Place and Route.

critical path

The slowest path through asynchronous logic between a set of source flip flops and a set of load flip flops that share a common clock signal. The delay through critical path (including clock to out and setup time) defines the minimum period the for the clock. A timing report on timing constraints will list all of the paths for a failed timing constraint from worst to best delay. The critical path for a timing constraint path is the first path listed.

daisy chain

A set of FPGA's wired together with for configuration. The configuration memory of the first device is loaded with its configuration data, then the next device is filled, and so on. When all of the FPGA's have filled their configuration memory, all of the FPGA's transition to the operation state in unison.

delay based cleanup passes

A feature in the place and route tools that tries to minimize routing delays on a completely routed design by choosing routing that has smaller delays.

Design Manager (dsgnmgr)

The main graphical implementation tool. The Design Manager, mantains versions of netlist files and revisions of implementation. files. It provides access to the Flow Engine, Timing Analyzer, Prom File Formatter, Hardware Debugger, and EPIC editor tools.

EDIF

Electronic Design Interchange Format. An industry-standard netlist format.

edif2ngd

Executable that translates an EDIF netlist file to an NGD netlist file.

EPIC (Editor for Programmable Integrated Circuits)

A graphical editor that provides a view of the physical implementation of your Xilinx design. EPIC features include:

• Ability to view CLB mapping, placement, and routing.
• Modification of CLB mapping, placement, and routing.
• Timing Anaylysis
• Ability to create custom physical macros to be incorporated in your design.

feedthrough

A CLB that is used to route to a signal. Feedthroughs allow a dense design to be more routable, although paths with feedthroughs have more delay. Feedthroughs can be identified using EPIC: CLB's show routing through them.

flexlm

Software that can distribute licenses to machines across a network.

Flow Engine

A graphical tool for executing the implementation flow on a design netlist. The Flow Engine performs the following processes: Netlist translation NGD, Map, Place and Route, and BIT file generation.

functional simulation

Simulation of a logical netlist using unit delays.

GUI (Graphical User Interface)

A graphical program used for accessing the implementation tools.

guide

When implementing a design, using the the map, place, and route results of unchanged logic from a previous implementation. Guiding an implementation can significantly reduce the implementation time, since the tools only need to spend time processing the parts of the design that have changed. There are two guide modes available with the FPGA implemenatation software: Exact and Leveraged. With exact mode, the unchanged logic can not be modified in the current implemenation. With leveraged mode, the unchanged logic is used as a starting point and can be modified by the current implementation.

Hardware Debugger

A graphical tool for configuring an FPGA or a daisy chain of FPGA's directly from a computer. The Hardware Debugger can take a BIT file or PROM file as an input.

IOB (Input Output Block)

A physically co-located group of buffers, latches, flip flops, and input/output pads used for sending signals off of the FPGA and receiving signals onto the FPGA.

IEEE (pronounced "I triple-E")

Institute of Electrical and Electronics Engineers.

LogiBLOX

A graphical tool for creating digital logic macros that are optimized for Xilinx FPGA's.

LUT (Look Up Table)

A block of logic in a CLB that uses SRAM technology to implement asychronous digital logic.

map

An executable that takes an NGD netlist and groups the logical elements into CLBs and IOB's. Map outputs the data into an NCD file.

multi-pass place and route

A place and route option that runs multiple place and route iterations on a design. Each iteration is executed with a different cost table values, so the results of each iteration are different. Each iteration is scored, and the best iterations are saved.

NGA (Native Generic Annotation)

An FPGA logic netlist file that is equivalent to an NGD file, but is produced by ngdanno during the backannotation process.

NCD (Native Circuit Database)

An FPGA file that holds mapping, placement, and routing data about a design implemenation. A valid NCD can hold mapping information, or mapping/routing information, or mapping/placement/routing information.

NGD (Native Generic Database)

An FPGA file that holds logical netlist information about a design.

NGM (Native Generic Mapping)

An FPGA file that holds information about optimized logic and netlists. An NGM file is used by the backannotation process to reconstruct the original netlist from the optimized NCD netlist for timing simulation. This enables you to use the functional simulation testbench in timing simulation.

ngdanno

ngd2edif

Command line executable that translates an NGD or NGA netlist to and EDIF netlist for simulation purposes.

ngd2ver

Command line executable that translates an NGD or NGA netlist to a verilog netlist for simulation purposes. If there is timing information in the NGD file then an SDF file will also be produced.

ngd2vhdl

Command line executable that translates an NGD or NGA netlist to a vhdl netlist for simulation purposes.

ngd2xnf

Command line executable that translates an NGD or NGA netlist to a xnf netlist for simulation purposes.

offset

A timing constraint keyword for specifying the off chip delay of a signal with respect to a clock.

par (Place And Route)

A command line executable for placing and routing a mapped NCD file.

PCF (Physical Constraints File)

A file generated by map that contains timing and location constraints of the logic in the physical domain. Map reads the constraints in the NGD file, which originally came from the netlist or the UCF file, and translates them into physical constraints.

place and route

The process of taking logic that has already been mapped to CLB's and IOB's, and determining which locations they occupy and what routing is used to connnect them. This process is performed by par.

post map simulation

Simulating a design after the mapping. The timing values for the logic are based on real block delays and estimates for the routing delays. Useful in performing a preliminary timing analysis before executing place and route.

post ngdbuild simulation

Functionally simulating a design after ngdbuild using unit delay timing. Useful for verifying synthesis results and verifying designs with components from varying front end tools.

post route simulation

Complete timing simulation after route that uses real block and real route delays. Useful for verifying that FPGA implementation meets all functional and timing requirements.

project

A data structure used by the Design Manager to hold information related to the implementation of your design: versions, revisions, implementation state, options used, etc.

PROM (Programmable Read Only Memory)

A chip used to store configuration data for an FPGA or a daisy chain of FPGA's.

PROM File Formatter

A graphical tool used for generating a PROM file from a configuration bit file.

promgen

readback

The process of reading data from an FPGA while it is executing a design. The data describes the FPGA configuration and the state of the flip flops in the design. Useful for performing verifying the correctness of the FPGA configuration and in performing an in circuit debug using the Hardware Debugger.

re-entrant route

The process of taking a partially routed design and continuing to route it using new options.

revision

A data structure in the Design Manager that refers to a complete or partial implemenation of a design. Multiple revisions can exist under a version, where each revision uses the same netlist but different implementation options.

RTL simulation

Pre-synthesis simulation of behavioral code.

SDF (Standard Delay Format)

A file that holds timing information for verilog simulation.

SuperBEL (Super Basic ELement)

A data structure in an NCD file that is created from a set of BEL's within a COMP that are editted using EPIC.

templates

A data structure used by the Design Manager and Flow Engine to hold option settings. There are two types of templates: Implementation and Configuration.

timing constraints

User directives to the map, and place and route tools indicating the desired speed for sections of the design. Specified in the input netlist or the UCF file.

timing simulation

Simulation after route that uses real block and real route delays. Useful for verifying that FPGA implementation meets all functional and timing requirements.

Timing Analyzer

A graphical tool for examing the speed of your FPGA implementation. You can examine delays on specific nets, performance of timespecs, and clock speeds.

trce

A command line tool for examing the speed of your FPGA implementation. You can examine delays on specific nets, performance of timespecs, and clock speeds.

Turns Engine

A feature that allow you to execute multi-pass place and route on simultaneously on UNIX machines.

UCF (User Constraints File)

A user created ASCII file for storing timing constraints and location contraints for a design implementation.

Verilog

An industry-standard hardware description language developed by Cadence Design Systems. Recognizable as a file with a .v extension.

version

A data structure in the Design Manager that refers to an input netlist. Multiple versions can exist under a project, where each version refers to the design netlist in various states of completion.

VHDL

VHSIC Hardware Description Language. An industry-standard (IEEE 1076.1) hardware description language. Recognizable as a file with a .vhd or .vhdl extension.

VHSIC

VITAL

VHDL Initiative Toward ASIC Libraries. A VHDL-library standard (IEEE 1076.4) that defines standard constructs for simulation modeling, accelerating and improving the performance of VHDL simulators.

X-BLOX

Blocks of Logic Optimized for Xilinx. A schematic-based synthesis tool where generic bus-width-independent symbols such as counters, adders, and data registers are used to implement architecture-optimized functions.

XNF

Xilinx Netlist Format.

xnf2ngd

Executable that translates an XNF netlist file to an NGD netlist file.