Once you’ve got an idea, how long does it take to turn that idea into a product? That depends on a large number of factors, including the developer’s expertise. Starting from scratch is always an option. Alternatively, building on a broader base can shorten delivery schedules, increase functionality, and possibly reduce end-product costs. Enter the reference design.
Vendors deliver reference designs to highlight their chips, modules, software, or services. But not all reference designs are created equal. At one end of the spectrum are complete, full-function designs with which designers typically extend or customize the solution. At the other end, the reference design becomes a platform. It highlights one or more features in a way that’s often easy to incorporate in another design.
Often, the completeness of a reference design is based on the target audience. Say you’re talking lap-tops. The changes to a reference design may only be the color and texture of the case. For example, VIA Technologies’ lightweight (1.87 lb) Nanobook UMD (ultra-mobile device) highlights the company’s VIA processor and chip set (Fig. 1). It was developed in conjunction with First International Computer.
Richard Brown, VP of corporate marketing for VIA Technologies, notes that this type of platform is often called “ready for market.” Developers can make minor changes to the case or more major enhancements, such as adding a Voice over Internet Protocol (VoIP) module. VIA will address the specific needs of its customers, or the customers may take the design and implement or enhance it.
With such an approach, customers can exploit the vendor’s expertise for components like the 1.2-GHz VIA C7-M ULV processor or high-speed interfaces. And, reference designs can be brought to the market rapidly at a minimal cost.
Sometimes, though, it’s not a matter of the difficulty of implementation. Instead, it’s a matter of taking advantage of a new idea. Many fully functional reference designs will need to be customized after they hit the market.
Developers interested in using Future Technology Devices International’s Vinculum VNC1L chip might want to start with DLP Design’s DLP-VLOG (Fig. 2). This sensor recording system works with a standard USB flash memory stick. The board contains a Microchip PIC16F88 plus a temperature and humidity sensor, a real-time clock, and two analog input channels for measuring voltages in the 0- to 30-V range.
The DLP-VLOG can be used in many applications as is, but it also is customizable since it’s a reference design. Developers can easily take the layout and change the kind of interfaces being polled with minimal alterations. And while reference designs presented by vendors may be as complete as these examples, they target customers who likely will make more significant changes to the design.
Advanced Micro Devices created its ETX Reference Design Kits (RDK) in conjunction with Logic Product Design (see “x86 System-On-Module Cuts Time-To-Market” at www.electronicdesign. com, ED Online 12443). The kits high-light AMD’s Geode processor chip, using a system-on-module containing the Geode. When using this approach, the module can be incorporated in a final design.
The complete schematics and support documentation are available, so a great deal of the system design work is already done. However, the reference design would still need significant enhancement for any product. Unlike the more complete reference designs examined earlier, these systems don’t target a specific application. These more general reference designs border on developments that are even further from a complete product.
I’ve been doing hands-on reviews of development kits for a number of years now (see “The Launch Of A New Web-Exclusive Department,” ED Online ID 8270). Over that time, I’ve seen significant improvements in both the sophistication of the platforms and the depth of support, especially on the software and tools sides.
In many cases, hardware designers augment the reference designs or development kits. But significant development often occurs before the custom platform is available. This is particularly relevant for module-based solutions like COM Express.
Most module-based solutions require a custom baseboard. Modules are often interchangeable with the baseboard. Typically, the modules are off-the-shelf components. This means they usually have a consistent architecture and differ in power consumption, processor performance, and other details that won’t significantly impact software development.
Kontron’s COM Express baseboard represents a good example of a base- board designed to expose all options for a COM Express module (Fig. 3). The schematics for the baseboard are available, as with most reference designs. In many instances, some or all of the design can be used in a product without any changes other than position on the baseboard.
This approach is especially useful when looking at newer technologies in the embedded space, such as Serial ATA (SATA), PCI Express, and ExpressCard. In fact, ExpressCard provides access to additional off-the-shelf products that plug into ExpressCard sockets. The same add-ons used with the reference design baseboard can be incorporated into a final product.
Some additions, such as a PCI adapter board, may or may not wind up in a final product. Hardware designers simply incorporate the PCI bridge chips and other hardware on the PCI adapter into a product design to reduce the footprint, power, or monetary costs, or for a host of other reasons. Still, software developers often can migrate their application from the reference design to the final design with minimal or no changes, reducing time-to-market.
Further down the line are quintessential development boards like the Evaluation Module from Spectrum Digital, which highlights Texas Instruments’ C5500 DSP (Fig. 4). This class of system isn’t designed to fit into a package or be incorporated into a system, though the chips and interfaces highlighted by the system would be. Portions of a product design may match that of the development board.
In many cases, the development board may be available in different configurations or with plug-in modules that let the system target specific application areas. Spectrum Digital has packages that target modem designs, while other packages do a better job of addressing multimedia applications. Development boards like Microchip’s Explorer 16, which has sockets for tiny PICtail 16 expansion boards, suit this type of add-on approach (see “One 16-Bit Architecture To Bind Them All,” ED Online 11142).
Rabbit Semiconductor’s SR9000 Smart Star System uses similar boards. But while the SR9000 is designed for incorporation into an embedded system, Microchip’s Explorer 16 is typically used to model an end product. The Explorer 16 often finds homes in lab environments, but it would rarely wind up inside a product like the SR9000.
Likewise, modular reference designs should not be confused with board-level systems like those based on standard bus architectures like PC/104. Products in the latter category are normally incorporated into a product rather than being used as the basis for a product design.
With modular systems, custom configurations can be easily assembled. But they still require hardware. Hardware availability may be limited in many cases, prompting developers to turn to virtual reference designs.
VIRTUAL REFERENCE DESIGNS
Simulated systems are often called virtual systems. In this context, the word “virtual” is distinctly different from, say, its context in “virtual machines.” Virtual systems simulate real reference designs. The level of simulation can vary greatly. For example, Virtutech Simics’ virtual system plat- form was used to simulate Freescale’s latest development kit, which highlights its multicore processor (Fig. 5).
Simics can provide cycle-accurate simulation or functional-level simulation. The simulation covers the processor in detail, but it gets less functional moving away from the processor to other interfaces found on the reference board. This isn’t uncommon, because the interfaces tend to be less standard and difficult to simulate easily, at least from a developer’s standpoint. Standard interfaces like Ethernet or serial ports usually are the easiest to address. In fact, the Simics simulation can route the processor’s Ethernet traffic to the host PC’s network.
Creating a simulation isn’t easy. A processor simulation can be rather complex, with the interface simulations nearly as complex. Yet another level of simulation, the user interface, is a graphical representation of the physical user interface versus the software user interface presented by an application. This more sophisticated level is employed in smart-phone simulations or similar platforms where the number of developers is high compared to the initial availability of hardware.
This brings up some of the additional advantages of virtual reference designs. Improved debugging is another edge simulations often hold over real hardware. They can expose information that’s even unavailable to a JTAG debug interface, such as pipeline state information. Likewise, virtual multi-core environments have the advantage of synchronized debugging and tracing that may not be possible, depending on the hardware.
There’s a major disconnect between the creation of virtual environments and system design. Typically, the system design is relatively complete before a virtual environment is developed and then finally delivered to developers.
The closest tools that start with models and target hardware include National Instruments’ Lab-VIEW Embedded and the Math- works’ Simulink. Both are model-based design tools. LabVIEW Embedded can generate application code and even FPGA code based on user-created models, but neither tool addresses board-level design details. The advantage of these tools is that the model simulation is inherent in the system design.
Simulations may be used for internal development or for third-party development. This may be due to availability or cost of the hardware. In the previous smart-phone example, the simulation often is available before the hardware. Likewise, the cost of distributing a software simulation is negligible, though licensing costs could be heavy.
WHAT TO LOOK FOR
Reference designs aren’t created equal. Designer requirements for reference designs aren’t equal either. What to look for and what is required will vary considerably. Likewise, the breadth of options will be quite different depending on the platform, application area, and cost.
Sources for reference designs are numerous, and they’re not restricted to chip vendors. Likewise, reference designs often run in second place in terms of implementation when it comes to development kits and vendor development cycles. Other places to look for reference designs include design houses, module and board vendors, and even distributors. Reference designs, especially virtual ones, are often available from companies further up the food chain, such as service providers.
The level of vendor support for a reference can vary considerably as well. At the low end, the only support might be what’s included in the box. At the other extreme, vendor representatives may provide hardware and software consultation, sometimes at considerable cost. However, that may be a bargain compared to developing and maintaining that level of competency in house.
Read the fine print in any licensing when examining reference designs and associated tools, support, and schematics. They may require additional fees or requirements to use the reference design within a product. Chip vendors rarely impose fees for board-level reference designs. Design houses, on the other hand, make a living from their services. Evaluation of a system using a reference design is typically a low or no-cost option, but final product delivery is another matter.
Also, take a look at any open-source software or hardware being used in conjunction with the reference design. Open-source licensing will bring up other considerations. For instance, will a company be willing to abide by open- source licensing like GPL, or would a different platform covered under a BSD license be more amenable to corporate goals?
Reference designs can save considerable work, but don’t assume anything. In most cases, they will be available, but the type and level of sophistication will vary. Fortunately, simply checking out a reference design is relatively low-cost.
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