What languages are used for real time systems programming?

Question

I didn't find any useful information about programming languages for real time systems. All I found was Real Time Systems and Programming Languages: Ada 95, Real-Time Java and Real-Time C/POSIX (some pdf here), which seems to talk about extensions of Java and C for real times systems (I don't have the book to read). Also, the book was published in 2001, and the information may be obsolete now.

So, I'm dubious whether these languages are used in real world applications, or if real time systems in the real world are made in other languages, like DSLs.

If the second option is true for you, what are the outstanding characteristics of the language you use?

Answer 1

Real time applications can be made in almost any language. The environment (operating system, runtime and runtime libraries) must however be compliant to real time constraints. In most cases real-time means that there's always a deterministic time in which something happens. Deterministic time being ussually a very low time value in the microseconds/milliseconds range.

Real time systems depend solely on this criteria, as the specificiations usually say something like 'Every x (period of time) (do something | check something)'. Usually this happens if the system interfaces with external sensors and controls life-saving or life-threatening systems.

I was working on an in-car navigation and infotainment system developed mostly in C/C++ with an operating system configured specifically to meet the real-time constraints to provide real-time navigation and media playback.

But this is not all to real-time systems: Usually the selection of algorithms in the entire system is made to have deterministic runtimes according to the Big-O notation, mostly using linear or constant time. Everything else is considered non-deterministic and thus not useable for real-time systems.

Answer 2

All of the real-time systems I have worked with were predominantly written in C with some bits of assembler, or written mostly in assembler with little bits of C. (Depending on whether we're talking the 90s and beyond, or the 80s, respectively.) However, some of the real-time systems I've worked with have used -- not exactly DSLs -- special homegrown code generators.

Answer 3

The book covers use of Ada 95, the Java Real-Time System and realtime POSIX extensions (programmed in C). None of these is directly a domain specific language.

Ada 95 is a programming language commonly used in the late 90s and (AFAIK) still widely used for realtime programming in defence and aerospace industries. There is at least one DSL built on top of Ada - SparkAda - which is a system of annotations which describe system characteristics to a program verification tool.

This interview indicates some of the classes and virtual machine changes which make up the Java Real-Time System. It doesn't mention any domain specific language extensions. I haven't come across use of Java in real-time systems, but I haven't been looking at the sorts of systems where I'd expect to find it (I work in aerospace simulation, where it's C++, Fortran and occasionally Ada for real-time in-the-loop systems).

Realtime POSIX is a set of extensions to the POSIX operating system facilities. As OS extensions, they don't require anything specific in the language. That said, I can thing of one C based DSL for describing embedded systems - SystemC - but I've no idea if it's also used to generate the embedded systems.

Not mentioned in the book is Matlab, which in the last few years has gone from a simulation tool to a model driven development system for realtime systems. Matlab/Simulink is, in effect, a DSL for linear programming, state machines and algorithms. Matlab can generate C or HDL for realtime and embedded systems. It's very rare to see an avionics, EW or other defence industry real-time job advertised which doesn't require some Matlab experience. (I don't work for Matlab ;) , but it's hard to over emphasis how ubiquitous it really is in the industry)

Answer 4

I am an avionics software engineer. I was able to participate in several development projects. The languages I used in those projects are: C, C++, and Real-time Java.

C is great. C++ is not so bad but C/C++ require strict coding standards for the safety considerations such as DO-178B.

I think Real-time Java is the way to go but I don't see many avionics applications, yet.

Korean jet trainer T-50 will have a mission computer running RT Java application serving HUD and MFD displays, and all of the mission critical functions.