Chapter 22: NetGen

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The Functional Simulation flow uses the following files as input:

•NGC —This file output by XST is used to create a UNISIM-based netlist suitable for using with IP Cores and performing post-synthesis functional simulation.

•NGD—This file output by NGDBuild contains a logical description of the design and is used to create a SIMPRIM-based netlist.

Notes on Functional Simulation for UNISIM-based Netlists

For XST users, the output NGC file can be entered on the command line. For third-party synthesis tool users, you must first use the ngcbuild command to convert all of the design netlists to a single NGC file, which NetGen takes as input.

The following command reads the top-level EDIF netlist and converts it to an NGC file:

ngcbuild[options] top_level_netlist_file output_ngc_file

Note: For information on NGCBuild, see Answer Record #21851 at http://www.xilinx.com/support.

Syntax for NetGen Functional Simulation

The following command runs the NetGen Functional Simulation flow:

netgen -ofmt{verilogvhdl} [options] input_file[.ngdngcngo]

verilog or vhdl is the output netlist format that you specify with the required –ofmt option.

options is one or more of the options listed in the “Options for NetGen Simulation Flow” section. In addition to common options, this section also contains Verilog and VHDL- specific options.

input_file is the input file name and extension.

Output files for NetGen Functional Simulation

•V file—This is a IEEE 1364-2001 compliant Verilog HDL file that contains the netlist information obtained from the input design files. This file is a functional simulation model and cannot be synthesized or used in any manner other than simulation.

•VHD file—This VHDL IEEE 1076.4 VITAL-2000 compliant VHDL file contains the netlist information obtained from the input design files. This file is a simulation model and cannot be synthesized or used in any other manner than simulation.

NetGen Timing Simulation Flow

This section describes the NetGen Timing Simulation flow, which is used for timing verification on FPGA and CPLD designs. For FPGA designs, timing simulation is done after PAR, but may also be done after MAP if only component delay and no route delay information is needed. When performing timing simulation, you must specify the type of netlist you want to create: Verilog or VHDL. In addition to the specified netlist, NetGen also creates an SDF file as output. The output Verilog and VHDL netlists contain the functionality of the design and the SDF file contains the timing information for the design.

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Xilinx 8.2i manual NetGen Timing Simulation Flow, Syntax for NetGen Functional Simulation
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8.2i specifications

Xilinx 8.2i is a significant version of the Xilinx ISE (Integrated Software Environment) that emerged in the early 2000s, marking an important milestone in the world of FPGA (Field-Programmable Gate Array) development. This version introduced a slew of advanced features, technologies, and characteristics that made it an indispensable tool for engineers and developers in designing, simulating, and implementing digital circuits.

One of the standout features of Xilinx 8.2i is its enhanced design entry capabilities. This version supports multiple design entry methods, including schematic entry, VHDL, and Verilog HDL, giving engineers the flexibility to choose their preferred approach. The integrated environment provides user-friendly graphical interfaces, making it accessible for both novice and experienced users.

Xilinx 8.2i's synthesis tools have been improved to enable more efficient design compilation and optimization. The new algorithms used in this version facilitate faster synthesis times while reducing power consumption and improving performance. Furthermore, it features support for advanced FPGA architectures, which allows for the implementation of more complex designs with greater efficiency.

The implementation tools in Xilinx 8.2i include advanced place and route capabilities, utilizing state-of-the-art algorithms for optimized resource usage. These tools enable designers to make better use of FPGA resources, ensuring that designs fit within the constraints of the target device while maximizing performance.

Another key characteristic of Xilinx 8.2i is its extensive support for various Xilinx devices such as the Spartan, Virtex, and CoolRunner series. This compatibility ensures that developers can leverage the powerful features of these FPGA families, including high-speed transceivers and DSP slices.

Xilinx 8.2i also places a strong emphasis on simulation and verification. The version integrates with various simulation tools, allowing for thorough testing of the designs before implementation. This reduces the risk of errors and ensures that the final product meets specifications.

In addition, this version includes support for design constraints, enabling engineers to specify timing, area, and other critical design parameters. By accommodating constraints, Xilinx 8.2i helps in achieving reliable and efficient designs tailored to project needs.

In summary, Xilinx 8.2i is a robust software development tool that enhances the design process for FPGAs. Its comprehensive features, including multiple design entry options, advanced synthesis and implementation tools, extensive device support, and strong simulation capabilities, make it a valuable resource for engineers and developers striving for innovation in digital design.
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