Why POSIX for embedded systems?

A common problem with realtime application development is that each realtime OS tends to come equipped with its own proprietary API. In the absence of industry standards, this isn't an unusual state for a competitive marketplace to evolve into, since surveys of the realtime marketplace regularly show heavy use of in-house proprietary operating systems. POSIX represents a chance to unify this marketplace.

Among the many POSIX standards, those of most interest to embedded systems developers are:

Note: For information about the many POSIX drafts and standards, see the IEEE website at http://www.ieee.org/.

Apart from any “bandwagon” motive for adopting industry standards, there are several specific advantages to applying the POSIX standard to the embedded realtime marketplace:

Multiple OS sources
Hardware manufacturers are loath to choose a single-sourced hardware component because of the risks implied if that source discontinues production. For the same reason, manufacturers shouldn't be tied to a single-sourced, proprietary OS simply because their application source code isn't portable to other OSs.

By building applications to the POSIX standards, developers can use OSs from multiple vendors. Application source code can be readily ported from platform to platform and from OS to OS, provided that developers avoid using OS-specific extensions.

Portability of development staff
Using a common API for embedded development, programmers experienced with one realtime OS can directly apply their skill sets to other projects involving other processors and operating systems. In addition, programmers with UNIX or POSIX experience can easily work on embedded realtime systems, since the nonrealtime portion of the realtime OS's API is already familiar territory.
Development environment
Even in a cross-hosted development environment, the API remains essentially the same as on the embedded system. Regardless of the particular host (Linux, Windows,...) or the target (x86, ARM), the programmer doesn't need to worry about platform-specific endian, alignment, or I/O issues.