Imagine a scenario in which your design team has received the marketing department's requirements for a next-generation SoC design. But as often happens, before you can finish the lengthy design cycle, the marketers wave a red flag. The market for the end product on which the SoC is based has shifted and the device's functionality must be adapted.
Now you don't know how to respin the chip in time. Should you (a) jump off a bridge, (b) scream at marketing, or (c) consider a shift to a design methodology that not only accommodates SoC design needs from one project to the next, but also allows you to quickly modify a project late in the game, without a total redesign?
The correct answer, of course, is (c). That answer is embodied in a design methodology known as platform-based system-on-a-chip (SoC) design.
Platform-based SoC design is a way to remove a great deal of the risk associated with traditional SoC design methods. It offers numerous advantages, such as the ability to easily build-in differentiating features and to reuse proven design elements in derivatives of earlier designs. It's scalable enough to allow designers to plug multiple iterations of intellectual property (IP) into a design. Such methodologies also save time by virtue of the fact that designs start out by leveraging a pre-existing initial design using predefined and preverified IP cores, buses, and software.
Typically, designers will select a core platform—a processor subsystem with some integrated specialized IP and standard buses—onto which memory, complex peripherals, processor boot code, the operating system (OS), and applications will be automatically connected. Support tools will generate the design along with the development-tool environment required to create and verify the design.
Definitions of the methodology vary to some degree. Most practitioners, though, would agree that a platform-based SoC design is one in which architectures, IP, connectivity, and verification suites for an SoC are reused within a structured, repeatable design environment, with the goal of minimizing design-cycle time. The basic premise behind the need for a platform solution is that time-to-market outweighs maximum optimization.
"A platform-based methodology enables SoC designers to focus on the part of the design that differentiates their design from any other," explains John Wilson, business development manager for the Platforms Group of Mentor Graphics' SoC Verification Business Unit. The goal is the ability to generate derivatives of a basic design with quick feature upgrades without modifying the basic topology.
One of the main time-to-market advantages of platform-based SoC design is the ability to create virtual prototypes, which are also known as virtual platforms (Fig. 1). These let designers start embedded software development and integrate hardware and software before they gain access to the physical prototype. Typically, embedded software development and debugging starts after hardware development. With a virtual platform, hardware-software integration can occur earlier. Therefore, not only are those bugs found and resolved, but the designer can also discover and resolve issues related to communications between the hardware and software, the timing of this communication, and the servicing of interrupts.
As a result, design respins are at the front end of the design process, and not after the physical prototype is returned, notes Pete Hardee, director of product marketing at CoWare Inc. "The hardware teams have the ability to add hardware to the core platform, verify the hardware using the 'real' application, update the hardware based on the results of running the real application, and continue this cycle with high confidence in the product's completeness."
The time-to-market emphasis at the expense of design optimization means that some application classes for SoCs lend themselves more readily to a platform approach than do others. Most applications using platforms are in the telecom, wireless, and consumer multimedia domains. One reason is that these domains have the most pressing time-to-market requirements, with design cycles of less than six months. These domains also benefit from the critical mass of existing standards, such as Bluetooth and W-CDMA, that can be implemented as platform libraries and then reused throughout a large variety of designs.
Other mainstream applications are systems with a raft of potential features or applications for disparate markets. "For example, a 3G cell phone is ideal," Hardee says. "Different 3G phones with varying features might appeal to different markets—teens versus business executives, for example. Other potential uses include communications and Internet appliances."
After you have analyzed your needs and determined that a platform-based approach to SoC design is right for you and your team, you must confront certain issues and answer some questions before comfortably taking the plunge.
Right up front is the added cost of switching to a new methodology. If you decide the cost is too high, you could be forced to stop right there and stick with the traditional ASIC SoC approaches. The added cost comes not only from creating, acquiring, or licensing IP, but also from the expertise required to support and upgrade such technology.
The hardest thing about platform methodologies, remarks Jeff Jussel, director of global programs for Mentor's Consulting Division, is the overhead required for initial platform setup. "To do it properly, much has to be known about the target SoC applications, verification of those SoC designs within their system environments, the preferred design environment, and even the company organization and culture," Jussel explains.
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