Military Embedded Systems

For an RTOS, often less is more


April 02, 2008

John A. Carbone

Express Logic

The choices include that complex RTOS you've used before, Linux, or a lightweight RTOS that can speed deployment to the field and provide a smaller footprint, making long-life support much simpler.

The choices include that complex RTOS you've used before, Linux, or a lightweight RTOS that can speed deployment to the field and provide a smaller footprint, making long-life support much simpler.

For many military systems, RTOS selection took a sharp turn
with the advent of Linux. Developers, enamored with Linux as a free, open
source desktop OS, felt that it could be used as a target OS for their
applications. These developers saw the cost-free licensing, absence of
royalties, and availability of full source code of Linux as compelling reasons
to use it in their next project.

Before Linux, such applications had traditionally been the
purview of large proprietary RTOSs offering robust arrays of services. These
complex RTOSs provide the needed capabilities that often include virtual
memory, Multiple Independent Levels of Security (MILS), and volumes of
middleware for security, communications protocols, and support for a vast array
of development systems. While Linux and complex RTOS products offer attractive
capabilities, they may not be the best fit for ALL military applications.
Often, a less complex RTOS may be a better choice in the long run.

The familiar has a price

Consider the fact that Linux distros and "heavy" RTOSs can be
relatively difficult to learn and use due to their complexity. Linux includes
hundreds of system services, a process-model virtual memory architecture, and
tens of millions of lines of open source code. High-end large commercial RTOS
products also include many features and lots of code, making them a challenge
to master. Both also are challenged to be responsive to real-time events, since
their complexity necessarily slows down their performance. Finally, while Linux
is perceived to be "free," the developer must assume the burden of
configuration, training, and support, or pay someone else to provide those
services. Likewise, complex proprietary RTOSs tend to be expensive, and many
include royalties per unit manufactured.

In contrast, some
military systems demand low-cost development and rapid deployment, and for
those systems, Linux or a complex RTOS may not be the best choice. For those
systems - those that do not demand hundreds of RTOS services, virtual
memory, and the like - a less complex RTOS is often a better fit. There
are many COTS RTOS products available that offer fewer services to learn, with
less overhead in their less-complex architecture. These options deliver smaller
code size, an easier-to-learn API, and better performance. Plus, many less
complex or lightweight RTOS offerings include the full source code and
royalty-free licensing of Linux, without the size, performance, or security
concerns that come along with open source software.

Now, after several years of experimenting with Linux, and
struggling with sluggish, complex, royalty-bearing proprietary RTOSs,
developers of these less-demanding military applications - like their
colleagues in commercial markets such as consumer devices, medical equipment,
and industrial controls - are finding that their projects are more likely
to be completed on time and on budget through the use of a streamlined, fast,
inexpensive RTOS thatís just right for their application.

Choose less, to get much, much more

We encourage developers to think twice before selecting that
old, familiar RTOS for a project that doesnít demand its complexity. Such
developers are often better served by using a simpler RTOS for those applications
that donít need all the capabilities of a complex RTOS. Many military embedded
real-time systems need just a few basic RTOS capabilities such as
priority-based preemptive scheduling, dynamic memory allocation and recovery,
inter-task message passing, interrupt management, resource-locking semaphores,
timers, and the like.

Addressing these basic needs, a lightweight RTOS can satisfy
a number of applications in military electronics, including portable,
battery-powered devices, cameras, remote sensors, and even avionics.
Certification efforts (for those military systems that elect to follow DO-178B,
EAL, or similar standards) are simplified through access to the full source
code of the RTOS and by the very small amount of code thatís included in the
deployed system. Developers of these devices can minimize development time by
choosing a lightweight RTOS that addresses their needs without excess
complexity. Shortening development time pays dividends in lower development
costs, faster deployment, and greater value. They also can benefit from a
smaller memory footprint and faster real-time performance. For these
applications, "less" actually is better, and delivers "more" for the developer.

The "less is more" adage is supported by findings in a recent
survey of embedded developers by Embedded Market Forecasters (EMF) (
This survey reveals that developers who recently used certain RTOSs tended to
complete their projects on time or ahead of schedule more frequently than those
who used other operating systems. This observation indicates that the RTOS
used plays a role in the timely completion of embedded development projects.

The lesson: "Avoid overkill"

This "less is
more" approach is attractive to some military system developers that
otherwise might opt to use Linux or a complex RTOS. Linux and large RTOSs are
good technology and might be ideal for many military applications, but they are
not the best choice for all applications. Developers are well advised to
consider this distinction. Projects with modest requirements are common, and
those projects might be better suited to one of the many lightweight RTOSs on
the market. For fast time to market, often "less is more."

John A. Carbone,
vice president of marketing for Express Logic, has 35 years of experience in
real-time computer systems and software, ranging from embedded system developer
and FAE to vice president of sales and marketing. Prior to joining Express
Logic, he was vice president of marketing for Green Hills Software. John has a
BS in Mathematics from Boston College. He can be contacted at [email protected].

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