Embedded Systems Design Europe - February 2008 - (Page 19)

feature the resulting HDL code. HDLs are a common and popular approach to FPGA design. You can create the source code with any text editor. Special HDL editors like CodeWright and Scriptum (a free HDL text editor by HDL Works) offers features such as HDL templates and highlighting reserved words not found in ordinary text editors. HDLs can be generic (supported by multiple simulation and synthesis tool sets) like Verilog or VHDL (Very High Speed IC HDL), or vendor-speciﬁc like Altera’s Hardware Description Language (AHDL), which is only recognizable by Altera’s design tool set. There are two writing styles for HDL designs, structural or behavioral. Structural ﬁrmware is the software equivalent of a schematic capture design. Like schematic capture, structural designs instantiates or uses vendorspeciﬁc components to construct the desired digital functions. This type of HLD ﬁrmware is vendor-dependent like its graphical counterpart and has the same disadvantages. Like schematic capture designs, repeating the design process is necessary for different vendors. Behavioral HDL ﬁrmware describes digital functions in generic or abstract terms that are generally vendor independent. This provides enough ﬂexibility for code reuse in different vendor’s FPGAs so little or no code modiﬁcation is required. Advantages of behavioral designs are its ﬂexibility and time and cost-savings, and it offers little to no vendor dependence. For designs that require vendor speciﬁc resources, such as RAM, only those components must change for different vendors. VHDL and Verilog are the most popular HDL languages. VHDL ﬁles consist of three main parts: library declaration, entity declaration, and architecture section. While not required by VHDL, an optional heading section should be included. This section should contain pertinent information, such as the designer’s name, ﬁlename, a brief summary of the code, and a revision history. Listing 1 shows an example of a VHDL ﬁle’s behavior. Because HDLs 19 each method has its advantages and disadvantages, HDLs generally offer the greatest design ﬂexibility. SCHEMATIC CAPTURE Schematic capture, the graphical depiction of a digital design, shows the actual interconnection between each logic gate that produces the desired output function(s). Many of these logic-gate symbols involve proprietary information making them available to the designer only through the speciﬁc vendor’s component library. Schematic capture designs that mainly consist of proprietary symbols make the design unrecognizable by competitors’ FPGA development tools. The proprietary na- ture of this type of design makes it vendor dependent, and the entire design process must be repeated if a different vendor is used. Examples of schematic capture tools are Viewlogic’s ViewDraw and HDL’s EASE. The main advantage of schematic capture is that the graphical representation is easy to understand. However, its major drawback is an increase in cost and time to reproduce a design for different vendors due to the design’s proprietary nature. HDL METHOD Hardware description languages (HDLs) use code to represent digital functions. “Firmware” often refers to www.embedded.com/europe | embedded systems design europe | JANUARY – FEBRUARY 2008 018-019-020-021-022-023-024-025-19 19 7/02/08 11:25:58 http://www.embedded.com/europe

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Embedded Systems Design Europe - February 2008 Contents ARTEMIS and ENIAC Get Parlimentary Approval Product Teardown Videos Come On Screen Esterel and Abslnt Integrate Products Microsoft Opens Windows to Networked Embedded Applications Trango Embeds Virtualization Tool in Cavium's Multicore CPUs MindTree - ADI Develop Security DVR Platform NXP Extends Deal with ARM to Cover MCUs Automotive and Embedded to Dominate DATE 08 ZigBee Spec Gets Smart On Energy Updated Card Spec Provides for Power-On Boot The Basics of Embedded Multitasking On a PIC Cover Feature: The Art of FPGA Construction Is Symmetric Multiprocessing For You? Accelerating MATLAB Using MEX-Files ARM Provides the Microcontroller Solution Embedded World Advertising Contracts

Embedded Systems Design Europe - February 2008

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