Assembly required: using reference-design resources

The amount of free or low-cost design support, including application-specific reference designs, available to designers evaluating processors continues to increase. Only a few years ago, when a designer wanted to evaluate a processor, silicon vendors provided not much more than a sample chip and a data sheet or an application note with instructions for how to hook up to the processor and start working. They provided little to no integration support, leaving the designer on his own.

This minimalist approach to selling chips eventually gave way to silicon vendor's providing more information, software-development tools, and hardware kits, which make it easier for designers to more quickly evaluate and incorporate chips into designs. The impact of this change in marketing strategy is so pronounced that, years after the industry's widespread adoption of it, silicon vendors are still quick to point out how they provide much more than just a chip and data sheets—implying that their competitors are still doing it the old, minimalist way.

Processor vendors continue to improve and increase the amount of design support they offer. Development tools for processors continue to evolve beyond the early assemblers and now include ever more sophisticated analysis and debugging tools and access to online engineering-knowledge databases. Code libraries for target processors now include increasingly complex functions, often at no charge to designers. Most silicon providers offer an array of hardware kits that enable designers to quickly evaluate, prototype, and develop applications with target processor architectures. In many cases, designers can also obtain the schematics and Gerber files for these hardware kits.

In addition to offering increasingly more sophisticated software-development tools, reference designs represent a growing trend in chip marketing. A fully realized reference design is a predesigned system that specifies the processor, memories, buses, and peripherals, using whatever chips the silicon vendor is trying to sell. The vendor designs a pc board of the reference design and publishes the reference-design schematic, bill of materials, software, and Gerber files for fabricating it. These reference designs provide designers an opportunity to shrink their design schedules by enabling them to reuse a silicon provider's effort to implement the hardware and software for common functions.

Despite the growing importance of reference designs to silicon vendors to win design-ins, the industry faces a lack of common terminology for reference designs. Therefore, this article proposes a nomenclature and taxonomy to describe the various forms of a reference design (Figure 1). It organizes reference designs into tangible and paper resources.

A narrow definition for a reference design implies that the term applies only to complete, turnkey designs that are production-ready and close to or exactly what an ODM (original-design manufacturer) might use. These types of reference designs represent a significant investment for a silicon vendor and target perhaps only a few dozen customers that deal in high-volume applications. Rather than create another term for incomplete designs that are not turnkey, the proposed taxonomy loosely applies the term "reference design" to predesigned resources from silicon vendors that customers may use as final products or starting points for a design.

The form of a reference design varies by an application's complexity. The more complex the target application, such as a wireless application, the greater the need for the silicon vendor to develop a more complete reference design. For simple applications, such as one using 8 bits, full-blown reference designs can be overkill, and a detailed application may suffice. "Our application notes provide the pieces rather than the whole design," says Rodger Richey, an applications manager at Microchip.

The demand for and acceptance of reference designs also varies geographically. ODMs in Asia, most notably China and Taiwan, are more likely to use a turnkey reference design as is. Many companies in Japan strongly rely on in-house engineering and have little demand for reference designs. In the United States and Europe, designers often use reference designs as starting points for the commodity portions of their designs, so they can focus more of their engineering resources on value-adding features.

A step down from a turnkey reference design defines as much as 80% of a system and supports rapid prototyping using a set of target chips for a specific application. These kits may include hardware- and software-development tools, boards, software and firmware, standard interconnects, and third-party modules and libraries. They enable designers to quickly explore how to implement appropriate commodity functions and standard interconnect interfaces. The boards may be too large or not validated to be appropriate for use in production. The undefined portions of the reference design, from a hardware perspective, may include defining the interconnect interfaces to implement. From a software perspective, the kit may leave the user interface and value-added functions up to the designer for differentiation. These kits may also leave out components that a design team would replace with local equivalent components.

The remaining forms of reference designs—platforms, hardware kits, and paper resources—are usually referred to in more general, less application-specific terms; however, this article lists them as reference designs, because they also can serve as starting points for a design team. Stefan Wierzoch, senior marketing manager at Infineon, points out, "Our customers tell us they use portions of our starter-kit designs as starting points for their own designs."

Platforms usually target a broader market or a class of applications, such as handheld devices, rather than specific applications. They allow vendors to better amortize the design effort in the platform across a larger number of customers. They can often serve as development platforms with flexible sets of features, peripherals, and interconnect interfaces. Platforms can consist of devices and IP (intellectual property) from several companies, and they represent an integration and verification effort of all of the components. It is significant for a silicon vendor to include its parts in a multivendor platform design because, as Rich Kapusta, marketing director at Cypress, reveals, "Many customers use the same chips and memories as in the platform design, and that enables them to avoid the time and resources to integrate and verify equivalent but different components in the system."

The hardware-kit category covers board-level kits from silicon vendors. They are most commonly called evaluation, demonstration, or development kits, but may be referred to as starter kits, development platforms, or evaluation modules. In many cases, similar to strict reference designs, the silicon vendor makes available to designers some set of the schematics, Gerber files, drivers, object or source code, and bill of materials.

Development kits or platforms support broader use; they usually reside on larger boards with access points and interface resources to better support software development, testing, and debugging. To maintain the maximum flexibility, they tend to provide access and control circuitry to more peripherals and interconnect options than one application design might normally need.

An evaluation kit is similar to a demonstration kit but may include or allow for the addition of application-specific components to the board design. It should include test points and sample code so that designers can quickly determine whether the target chips meet their design requirements.

Demonstration kits contain application-specific components and provide a tangible example of how designers can use the target chips to implement an application design. These kits may not provide the same testing support as evaluation or development kits, and they offer little support for the designer to make extensions or modifications.

Development, testing, and manufacturing costs for a silicon vendor to create a tangible reference-design resource are significant, so for simple systems, it can be more economical for a silicon vendor to provide paper reference-design resources and software tools. The earliest application notes distributed with sample chips were a form of paper reference-design resource. Those devices and the applications they supported were simple enough and the production volumes were low enough that silicon vendors could not justify more than paper design resources. As the complexity of applications and devices continued to increase, providing more than paper design resources began to make business sense.

The design guides, tutorials, and application notes accompanying today's chips are usually more comprehensive than earlier application notes, and they complement the tangible hardware resources a silicon vendor offers to designers. The application notes may include the source code for software libraries and modules. For simple system designs with small technical and cost margins, using a sample schematic and source code as is may be too costly; designers may need to modify the design and code to meet the requirements at the minimum resource cost.

A reference-design resource itself is not a product. Although using a reference design can save a development team time and engineering effort, strictly speaking, a reference design is not a development-productivity tool; it is a tool for marketing chips and IP licenses. Silicon vendors fund and develop reference designs. They may contract third-party companies to assist them in designing and completing a reference design, but, unless the third party has some IP to license in the design, little opportunity exists for it to realize the same continuing revenue stream from the effort as the silicon vendor.

Strict reference designs that provide at least 80% of a design are application-specific because they have to balance and meet the technical and business requirements for an application. A general-purpose reference design could not offer the same level of optimization and balance as an application-specific design. A silicon vendor's decision to fund a reference design is a push-and-pull process. A silicon vendor offering an ASSP (application specific standard product) needs to prove that the device can perform. In other cases, many customers or one large customer may ask the silicon vendor to help solve a problem.

For simpler systems, many silicon vendors make their reference designs available at little to no cost to designers. For complex systems, a silicon vendor may make the reference design available only to high-volume customers, in part because creating a reference design incurs significant development costs. On the other hand, without the reference design, the silicon vendor might be unable to sell chips for complex systems. In this way, reference designs can help drive and accelerate the industry's adoption and deployment rate of complex features, such as supporting wireless interfaces, by commoditizing the basic engineering effort for those features. Because reference designs are predesigned systems, silicon vendors can complete them to such an extent that designers can use them to simplify the process for a development team to verify and obtain certification for its system. Saving a development team time and effort allows it to focus more on value-adding differentiation.

A concern with new reference designs arises when a silicon vendor commoditizes and makes available to a customer's competitors that customer's value-added or differentiating IP. The line between value-added differentiation and commodity is constantly shifting. Not long ago, TCP/IP (Transfer Control Protocol/Internet Protocol) stacks could command substantial licensing and royalty fees, but some silicon vendors are now offering such stacks for no charge as application-note components in their reference designs.

If reference-design resources are sales tools, it should be easy for designers to find out what's available on the Web. However, the process is not as straightforward as it might at first seem. For one, the inconsistent use of reference-design-resource terminology complicates what should be a simple keyword search, such as "reference design for <my application>." Using the words identified in Figure 1's proposed taxonomy can improve a designer's search results.

Also complicating a designer's search for reference-design resources is the fact that many silicon vendors fail to actively market reference designs on the Web, relying instead on their direct-sales and distribution channels. The reasons for this situation are that the silicon vendors can neither justify the cost and effort to productize and properly support a general-availability reference design nor want to make it easy for their competitors to find out what they are doing and how they are doing it. Another part of the reason is that companies market to a few dozen customers differently from how they would sell to thousands of customers. Because reference designs are application-specific, they tend to have a small target-customer base; the exception to this rule is reference designs for standard interfaces, such as USB.

Each silicon vendor lists only its reference designs on its own Web page, so a designer needs to visit each vendor's site to identify and compare similar reference designs. Search the vendor's Web site under reference designs, design centers, or design resources; in general, silicon vendors sort their reference-design resources by target processor or type of application.

Until recently, no public, industrywide repository for reference designs had existed; Electronic Products (www.electronicproducts.com/refdesign.asp) now offers one online. EDN is integrating reference-design-resource information into its annual DSP and microprocessor directories. This new information should enable designers to more quickly find new reference designs from silicon and IP vendors and the type of applications and processors they target.