A Technical History of the SEI

Introduction to Real-Time Embedded and Cyber-Physical
Systems
Most mission-critical defense systems use embedded processors with hard real-time components
in which the software must process inputs from sensors and execute instructions to control devices.
Sensor data can arrive synchronously or asynchronously. Each data point is available only
for a short period (nano to micro seconds), and the output must be produced fast enough to provide
timely control. A terrain-following avionics system is an example: it must process the altimeter,
airspeed, and radar inputs in sufficient time to issue altitude controls to follow the terrain. The
processor may be performing other lower priority tasks, such as monitoring fuel.
Real-time constraints affect almost all Department of Defense (DoD) systems applications, such
as avionics, fire control, vehicle management, missile guidance, radar tracking, and unmanned air
vehicle (UAV) control. Indeed, the requirement to manage real-time constraints is one of the factors
that distinguishes DoD software from many civilian applications. While civilian applications
also exhibit real-time components, the DoD requirements are generally coupled with other factors,
including sheer size of the software, security, weapon system safety, and life dependence, that
make the real-time component critical [NRC 2010]. As the integration of the processor with the
physical system of sensors and controls has become ever tighter, the term cyber-physical has been
adopted to describe these systems.
The SEI Contributed to Early DoD Ada Adoption Effort for Real-Time
Embedded Systems
Prior to establishing the SEI, the DoD developed a new programming language called Ada. One
of the factors driving development of Ada was the desire to develop real-time software in a higher
level language supported by tools to manage the complexity. When the SEI began operating, the
DoD had mandated the use of Ada for all mission-critical systems, and DoD program managers
had serious concerns regarding early use of the language. Since this was clearly of strategic importance
to the DoD and future software-intensive systems, the SEI launched several efforts
aimed at addressing the technical and managerial questions about Ada adoption.
A number of commercial Ada compilers were coming to market. While each was required to pass
validation by the Ada compiler test suite, the supporting tools making up the software development
environment were largely disparate. This was the source of considerable confusion among
DoD program managers. The SEI set out to assess the maturity of various compilers and supporting
tools to determine their suitability to support DoD programs. For a variety of reasons, DoD
programs chose different embedded processors with different instruction set architectures for their
systems. Each of those instruction set architectures required different code generators, so that
while each could use the same validated compiler and each validated code generator would produce
code that correctly executed the Ada instructions, different code generators would have different
runtime characteristics.
The SEI established the Ada/Real-Time Embedded Systems Testbed to build the necessary infrastructure
to test the runtime performance of code generators. In addition to having the necessary
hardware to support testing the suitability of these processors for a given application, the SEI
testbed team had the expertise to conduct the testing so that DoD programs did not need to undergo
the expense of duplicating that capability. DoD programs that did not choose Ada as their
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