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Home > FPGA Technical Tutorials > Design Recipes for FPGAs Using Verilog and VHDL > Design Automation of FPGAs > Design Pitfalls

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Design Pitfalls

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The most common mistake that inexperienced designers make is simply making things too complex. The best approach to successful design is to keep the design elements simple, and the easiest way to manage that is efficient use of hierarchy. The second mistake that is closely

Flowchart of the simulated annealing methodpng

Figure 5.4

Flowchart of the simulated annealing method.

related to design complexity is not testing enough. It is vital to ensure that all aspects of the design are adequately tested. This means not only carrying out basic functional testing, but also systematic testing, and checking for redundant states and potential error states. Another common pitfall is to use multiple clocks unnecessarily. Multiple clocks can create timing-related bugs that are transient or hardware dependent. They can also occur in hardware and yet be missed by simulation. 

Initialization

Any default values of signals and variables are ignored. This means that you must ensure that synchronous (or asynchronous) sets and resets must be used on all flip-flops to ensure a stable starting condition. Remember that synthesis tools are basically stupid and follow a basic set of rules that may not always result in the hardware that you expect.

Floating Point Numbers and Operations

Data types using floating point are currently not supported by synthesis software tools. They generally require 32 bits and the requisite hardware is just too large for most FPGA and ASIC platforms.

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  • FPGA Virtex-4 SX Family 23040 Cells 90nm Technology 1.2V 668-Pin FCBGA
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  • Xilinx BGA-1148D
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