Compared to a standard USB peripheral, this entails adding analog capabilities (VBUS drive and control features, VBUS level-sensing logic), digital logic (host capability, support for SRP and HNP protocols), software (driver support for items on the Targeted Peripheral List), and system functions (a way to communicate messages to the user). So, designing an OTG peripheral-only device takes just a little more effort than a standard USB peripheral, while the design of a dual-role device is significantly more complex.
The degree to which this increase in complexity impacts the product design effort and schedule depends greatly on the type of product, the starting point of the effort (modifying an existing design versus beginning a new design from scratch), the available components, and the chosen design method.
As with a standard USB system, a designer can choose to implement the USB portion of the design in one of three ways: purchasing a full solution, using a USB microcontroller, or designing a custom IC. Obviously, the design effort involved in the USB interface itself decreases with the completeness of the chosen solution. Of course, the usual tradeoffs between flexibility, cost, suitability, and design time and effort apply.
The difficulty and risk of designing an OTG dual-role device will decrease significantly over the next few years as greater numbers of robust, complete building blocks come on the market. With any choice, there are overall system considerations that apply to any OTG device. An example is the need to communicate messages to users.
Additional testing is the final component. OTG devices need to be well tested for conformance to the specification and flawless operation to create a good user experience. A validation plan should include careful consideration and testing of all parameters specified by both the USB specification and OTG supplement. The OTG Compliance Plan is a good place to start validation.
Current Status: Developed by a committee of representatives from a cross-section of the industry, the OTG supplement already has broad support from connector makers, IP vendors, silicon providers, software houses, and equipment manufacturers. Based on this support and committed involvement, it's anticipated that OTG devices will appear on the market soon. Now that the specification has been released, a major focus of the committee is education and evangelization. Recently, the committee sponsored several industry training sessions in the U.S., Asia, and Europe. Such activities will continue in the future.
Moreover, several areas for future work and companion specifications are still in development. The OTG Committee is finalizing the OTG Compliance Plan, a specification that defines the compliance tests to ensure OTG devices meet the specification requirements. There also is considerable work under way to define OTG Types.
There's no better way to understand the new features and correctly implement them in your own products than by directly working with the specifications—and with the experts who designed them. To further explore USB, or to download the USB specification and ECN, visit www.usb.org/. To learn more about OTG, download the OTG supplement, read explanatory articles, learn about OTG events, and join the OTG Committee mailing list, see www.usb.org/developers/onthego/. Any company that wishes to access this information must be a registered member of the USB Implementers Forum (USB-IF).
Along with the proliferation of powerful portable devices come new problems in communications protocols. USB OTG addresses these problems. The specification is available now and ready to help enable the next generation of mobile computing.