In our design, the HRL utilizes OpenGL to render to take advantage of hardware acceleration, and supplies an API to allow HMI embedded logic or external applications to manipulate elements of the HSL database at run time. The user application primarily interacts with the variables that define the interface to the HMI via any means, including passing variables and events over an avionics data bus if required. A key feature of the HRL is that, as the underlying graphics API implementation changes, the HRL can be modified to address different underlying graphics APIs with no change to the database format or capabilities of the system. This provides a significant advantage in managing obsolescence.

The HRL also contains the control state management system, otherwise known as the “window” manager. This component has the capability to accept user input and reflect user events from a cursor control device or keyboard back to the variable system. The variable system maintains a table of events that are user interactions with the system. Events can be accessed at different levels of the HMI logic to accomplish both low-level control and higher-level system actions. Figure 4 shows how the tools and run-time components of the dynamic display system fit together.

The data-driven avionics HMI solution provides extensive benefits:

• Early Testing Advantages — While modeling the HMI components, the ability to fully exercise the HMI using the tool environment is valuable. System designers are able to create complete HMI models without being concerned with underlying system details or code.
• Code Elimination — The system eliminates much coding in the development and integration of applications. Up-front modeling replaces coding, and integration based on HSL proves very flexible in reusing HMIs across application form factors.
• Increased Performance — The rendering library has been deployed on embedded systems ranging from PDAs and automotive processors to embedded avionics computers. The optimization approach supported by the HSL solution has resulted in very good performance on a wide range of avionics target computers.

Overall, a data-based HMI approach has demonstrated substantial benefits that are key to an open-architecture avionics solution. The elimination of code, while retaining the optimized nature of a code solution, is the key benefit of the technology. The benefits include reduced system complexity, simpler system architecture, and easier system development and maintenance. An example of a set of avionics displays is shown in Figure 5. Each display is a HSL separate database output from the modeling tool and composited together.

This article was written by Mark Snyder, director of Embedded SW Engineering for Quantum3D, Glendale, AZ. For more information, click here.