The SCA specification defines the CF as the essential core set of open application layer interfaces and services. It provides an abstraction of the underlying software and hardware layers for software application designers.
The CF includes the base application interfaces that can be used by all the software applications and the framework control interfaces that provide system control. These include:
- The Domain Manager
- The Device Managers
- The Framework Service that supports core and non-core applications
- The Domain Profile that describes the properties of the hardware devices and the software components of the system and domain profiles
These are written in eXtensible Markup Language (XML), which is a protocol used for web design and a number of software development applications.
CORBA ORB Middleware
As a message-passing technique, CORBA is used for distributive processing throughout the software environment. Distributive processing is a fundamental aspect of the SCA specification, and CORBA is a widely used middleware for cross-platform frameworks. These cross platforms can be used to standardize client and server operations when using distributive processing.
All CF interfaces are defined in Interface Definition Language (IDL) that is independent of programming language and can be compiled into programs created in C++, ADA, or Java. The SCA IDL defines operations and attributes that serve as a contract between the components.
Operating System The OS layer is defined by SCA to include real-time embedded OS functions that provide multithreaded support for applications including the CF applications.
The architecture requires a standard OS interface for OS services to facilitate portability of applications. The OS must comply with the Portable Operating System Interface (POSIX), an established industry standard. The SCA uses a small subset of the POSIX definition, specifically the real-time controller system profile.
Network Services
The SCA specification calls for Network Services that allow commercial components to support multiple unique serial and network interfaces. As a result, possible serial and network physical interfaces include RS-232, RS-422, RS-423, RS-458, Ethernet, and 802.11 wireless protocols. To support these interfaces, low-level network protocols may be used including point-to-point (PPP), serial line Internet protocol (SLIP), and others.
Elements of waveform networking functionality also may exist at the OS level. An example of this would be a commercial IP stack that performs routing between waveforms.
Board Support Package
The BSP, the last layer, is the closest to the hardware functionality of the actual hardware platform. The SCA specification allows for operation on commercial bus architectures, so the operating environment can support reliable transport mechanisms. These may include error checking and correction at the bus support level. Possible standards are VME, PCI, CompactPCI, Firewire, and Ethernet.
Again, the SCA operating environment recognizes the use of red and black components of the system. In Figure 3, you can see that there are two different sets of BSPs, one for each side of the application.
