Embedded C is a set of language extensions for the C Programming
language by the C Standards committee to address commonality issues that exist
between C extensions for different embedded systems. Historically, embedded
C programming requires nonstandard extensions to the C language in order to
support exotic features such as fixed-point arithmetic, multiple
distinct memory banks, and basic I/O operations.
In 2008, the C Standards Committee extended the C language to address these
issues by providing a common standard for all implementations to adhere to. It
includes a number of features not available in normal C, such as,
fixed-point arithmetic, named address spaces, and basic I/O hardware
addressing. Embedded C uses most of the syntax and
semantics of standard C, e.g., main() function, variable definition, datatype
declaration, conditional statements, loops, functions, arrays and strings,
structures and union, bit operations, macros, etc.
A Technical Report was published in 2004 and a second revision in 2006.
Necessity During infancy years of microprocessor
based systems, programs were developed using assemblers and fused into the
EPROMs. There used to be no mechanism to find what the program was doing. LEDs,
switches, etc. were used to check for correct execution of the program. Some
‘very fortunate’ developers had In-circuit Simulators, but they were too
costly and were not quite reliable as well. As time progressed, use of
microprocessor-specific assembly-only as the programming language reduced and
embedded systems moved onto C as the embedded programming language of choice.
C is the most widely used programming language for embedded
processors/controllers. Assembly is also used but mainly to implement those
portions of the code where very high timing accuracy, code size efficiency,
etc. are prime requirements. As assembly language programs are
specific to a processor, assembly language didn’t offer portability across
systems. To overcome this disadvantage, several high level languages, including
C, came up. Some other languages like PLM, Modula-2, Pascal, etc. also came
but couldn’t find wide acceptance. Amongst those, C got wide acceptance for
not only embedded systems, but also for desktop applications. Even though C
might have lost its sheen as mainstream language for general purpose
applications, it still is having a strong-hold in embedded programming. Due
to the wide acceptance of C in the embedded systems, various kinds of
support tools like compilers & cross-compilers, ICE, etc. came up and
all this facilitated development of embedded systems using C. Assembly
language seems to be an obvious choice for programming embedded devices.
However, use of assembly language is restricted to developing efficient codes
in terms of size and speed. Also, assembly codes lead to higher software
development costs and code portability is not there. Developing small codes are
not much of a problem, but large programs/projects become increasingly
difficult to manage in assembly language. Finding good assembly
programmers has also become difficult now a days. Hence high level languages
are preferred for embedded systems programming.
Advantages It is small and simpler to learn,
understand, program and debug. Compared to assembly language, C code
written is more reliable and scalable, more portable between different
platforms. C compilers are available for almost all
embedded devices in use today, and there is a large pool of experienced C
programmers. Unlike assembly, C has advantage of
processor-independence and is not specific to any particular
microprocessor/microcontroller or any system. This makes it convenient for a
user to develop programs that can run on most of the systems.
As C combines functionality of assembly language and features of high level
languages, C is treated as a ‘middle-level computer language’ or
‘high level assembly language’. It is fairly efficient.
It supports access to I/O and provides ease of management of large embedded
projects. Java is also used in many embedded
systems but Java programs require the Java Virtual Machine, which consumes a
lot of resources. Hence it is not used for smaller embedded devices.
Other High-level programming language like Pascal, FORTRAN also provide some
of the advantages. References