Applications Of Assembly Language

Title: Advantages and Disadvantages of Using Assembly Language in Embedded Systems Introduction Assembly language is a low level programming language for programmable devices and mainly computers. Today, assembly language is used primarily for direct hardware manipulation and to access to specialized processor instructions, or even to address critical performance issues. In a book specialising in assembly language, the author (Blum, R. 2005) explains the general use of assembly language, where it is stated “assembly language enables programmers to directly create instruction code programs without having to worry about the many different instruction code set combinations on the processor” [1]. Typical uses are device drivers, low-level embedded systems, and real-time systems. The assembly language is converted into executable machine code by an “assembler” which basically is a utility program. The process of conversion is called “assembling the code” or even “assembly”. Assembly language is machine specific and considered a "low level" language. This means that the code and syntax is much closer to the computer's processor, memory, and I/O system. A high level language is designed with keywords, libraries, and a syntax that introduces a high level of abstraction between the language and the hardware. Since a computer’s behaviour is defined by its instruction set, the logical way to learn such concepts is to study assembly language.

Until today, there are still programmers who uses assembly language in application development. Why is this so? Because there are advantages of using it and these advantages are very significant hence assembly language is currently still popular and in demand. However, everything has its advantages and disadvantages, so in this report we are going to discuss the advantages and disadvantages of using Assembly Language in applications such as embedded systems. An embedded system is a microprocessor based system that is incorporated into devices to control and monitor the functions of the components of the device. Where are embedded system used? From the range of a microwave oven to a nuclear reactor. Embedded systems are usually designed for performing specific tasks. It is programmed by the designers of the system and generally cannot be programmed by the end user.

Embedded systems should be very reliable since they perform only critical functions. For example, consider the embedded system is used for flight control, if the system should failed, disastrous consequences will occur. Hence embedded system programmers should take into consideration of all possibilities and write programs that do not fail. “Programming embedded system software typically involves more than one programming language. Normally, a high-level language such as C/C++ is used for application oriented tasks and a low-level assembly language for direct interaction with the underlying hardware. In most cases

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those languages are closely interwoven and the assembly is embedded in the C/C++ code” *2] is stated by (Fehnker, A., Huuck, R., Raunch, F., Seefried, S., 2008). Embedded systems should respond to events as soon as possible. For instance, a patient monitoring system should process the patient’s heart signals quickly and immediately notify if any abnormal signals is detected. Since embedded systems are used for performing specific functions, specialized hardware is used. For example, embedded systems that monitor and analyse audio signals use signal processors. As embedded systems are extensively used in consumer electronic systems, they are cost sensitive and thus their cost must be low. (Ebrahim, A., 2010) points out that “the transition to embedded systems development is difficult without a reasonable understanding of assembly language and computer architecture“, he further states that “as embedded computing enters almost every aspect of the modern technology landscape, from intelligent gadgets of all kinds to remote and autonomous systems, not having this knowledge becomes a fundamental impediment to seeing and being able to seize the many opportunities for participating in this interesting and rapidly expanding area” [3]. “Unlike personal computers that run a variety of applications, embedded systems are designed for performing specific tasks. An embedded system used in a device (for instance the embedded system in washing machine that is used to cycle through the various states of the washing machine) is programmed by the designers of the system and generally cannot be programmed by the end user“ [4 ] is a brief description of embedded systems provided by (Reddy, P. M., 2002) . So, embedded systems have requirements that differ significantly from general purpose computers. (Reddy, P. M., 2002) states the fact that “The main goal of an embedded system developer is to design a lowest cost system that performs the desired tasks without failing “and later affirms that “recent developments in hardware-software co-design permit trade-offs between hardware and software for cost-effective embedded systems” *5]. This can be supported by the fact that algorithms can be implemented in hardware or software. While the hardware approach improves performance the software approach provides flexibility. And through this aspect of efficiency being achieved, this may not only comply to the wants and needs of the company or a client but allows the business to operate efficiently.

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Advantages of Using Assembly Language in Embedded Systems First of all, assembly language uses mnemonic codes. Mnemonic codes are an abbreviated term that is used to define a specific command. These codes are shorter and yet provide the same function as the original term but are more efficient to enter. Mnemonics allows us to access a wide variety of commands at a much quicker pace without the need to type out extended phrases. (Shibu, K. V., 2009) states that “in Assembly language based design, it (embedded system) is developed using the Assembly language specific to the target processor. The Assembly code is converted to machine specific code by an assembler” *6]. We often require precise accurate timing and fast speed. Coincidently, assembly language is well known for these two specific features. Assembly language can be optimized for speed ensuring that applications are able to run as fast as possible. Assembly language offer the best choice for applications that requires very precise timing since there is no need for the code to be interpreted unlike high level languages that sometime may have delay during processing. “Assembly language lets programmers squeeze out the maximum performance from their application in terms of speed and memory” a statement provided by (Moyer, B., 2013) [7]. While assembly language is more primitive in the instructions that are available compared to a highlevel language, it is a huge improvement upon programming in the binary code of machine language. For example, “JMP” is a jump instruction that will transfer program flow to a new location. Basically this point of benefits is actually pointing out that using of assembly language actually saves time because of the prevention of using long codes. (Moyer, B., 2013) states that “programmers frequently use the assembly output of the C compiler to debug, hand-edit or hand-optimize the assembly code to maximize in performance in ways the compiler cannot. This lets them to go down to architectural details of their code and count instructions in order to obtain accurate timing characteristics of their application and look at the execution of their code at the machine instruction level” *8].

Assembly language is transferable across machines. Compared to machine code programs an assembly language program enjoys some portability and can be executed on computers of different types so long as there is an assembler there that is able to interpret the code into binary code for a particular machine. Portability is one of the strongest advantages of using assembly language. It has more portability compared to machines codes and yet shares the same flexibility of a high level programming language. (Aguiar, A. & Hessel, F., 2010) states that “Their functionality was also mostly determined by hardware, with software mainly consisting of largely device drivers, a task scheduler and some control logic, resulting in a low complexity of the software. Besides, these systems used to be closed, which means that during its lifetime, no change in the software is required” *9]. So, assembly language is used because it can be executed on firmware or processors which do not have any operating system (OS) or high level language compilers. To make it clearer, devices such as mobiles phones, dish washers , washing machines , water heaters , table fans and such are often

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require computer instructions that are written in assembly language because the code is a standalone item that can be executed without the overheads of a full computer system. This may actually decrease the cost of a business in order to operate an embedded system that does not need a yearly change or update in the software. (Moyer, B., 2013) states that “In some low-cost embedded systems with no support for other language (like C) compilers, such as small microcontrollers. Assembly is the only programming interface available. Situations where a highlevel language compiler does not provide support for all hardware features, you will ned to write the functionality (of the embedded system) in assembly, either in-line or as a separate function” [10]. Interaction with hardware is also one of the strong points of assembly language. Why is this so? Because assembly language can interact directly with the hardware hence it remains one of the best ways of interacting with hardware with many low level functions to read sensors or control components being done at a machine level. (Linggesmeyer, P. & Trapp, M., 2009) states that “embedded software must be tailored to heterogeneous hardware platforms and operating system to meet high performance demands despite limited resources such as (memory and searching power). This yields tailored, specific software platforms that are either created through the application and adaptation of the platform frameworks or developed specifically for an embedded system” *11]. Assembly language is able to access hardware drivers and system code hence having the privileges to access hardware, system control registers and etc. This benefit however may be difficult or impossible with the use of high level code. The code is so lightweight that it is optimized for size. Although storage space now a days are cheap but cache size is still such a critical resource that it may be useful in some cases to optimize a critical piece of code for size in order to make it fit into the code cache. Not to mention that assembly language has the same efficiency of execution as the machine level language. Because this is one-to-one translator between assembly language program and its corresponding machine language program.

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Disadvantages of Using Assembly Language in Embedded Systems However, in the case of language preferences, there are some programmers who prefer the use of C language over assembly language. In other cases, C language would be used as the main language while the assembly language would just be used for some routines. Same as can be said about a client’s (in the case of a company offering to develop an embedded system for a client), may also have some preferences about the language they may choose which may entirely affect the programming language choice of the programmer. This in turn complicates the language choice in the development of embedded systems. This can be seen in an article written by Michael Barr, an embedded systems developer himself, when a scenario was being put out in an Embedded Systems Conference in San Jose. The scenario was that an imaginary company has hired the attendees of the conference to operate as a consultant for their embedded software system that has been causing some issues with their new product development. Long story short, the company needed a complete redesign and implementation of a new firmware. The options of the languages used were narrowed down the two, Assembly language and C language. In the article, Barr analyses the difference between the two languages and how much it may suit to fit the conditions of the required specifications of the scenario. With a collaboration with an another embedded systems developer that specialises in assembly langue (Barr specialises in the development of embedded systems in the C language), two different firmwares were created and put through tests in order to determine how suitable they would be as a solution to the given scenario. At the end of it, Barr has come up with a surprising discovery; that the C language was more efficient than assembly language in terms of program efficiency. In the analysis Barr writes that “this race condition was exposed when my C code was unable to communicate with a remote system with which the assembly code had no trouble exchanging information. After two days in the lab, we finally determined that the true source of the problem was that the C code was twice as fast to respond to a sync command than the assembly language has ever been. With a shorter latency in the communication channel, a race condition in the remote software was exposed. Surprise, surprise, surprise...C had beaten assembly in terms of program efficiency” *12]. This may bring out the assumption that in theory assembly language may actually seem better which and in terms of application of the development of an embedded system, C language may be a better choice but it is not as it seems. The lesson here is the choice of the language and the intended use of the embedded system (whether it is heavy on the arithmetic functions or is it operable in the company’s terms). Based on the analysis done by Barr, the C language was only more efficient than the assembly language when a sync command was used. This proves that the efficiency of the language is only determined by the optimization of certain conditions in order to determine which of the languages are more efficient than the other. That and also the preferences of the programmer would determine which of the language that is used in the application of the embedded system itself. But Barr does advise that “choosing a language more

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tuned to the problem at hand made this system design easier, the implementations faster (by a factor of 10), and the whole project ran smoothly. The end result was a program that could be easily maintained and/or ported to new hardware” *13]. “This is not to say that the disadvantages of assembly language programming are any the less — assembly language is not portable and almost always has higher overhead when coding, debugging, and maintaining. But in these few areas of embedded systems development, the benefits occasionally outweigh the trade-offs. ” *14], a statement made by (Ebrahim, A., 2010) The statement above may shed some light towards why assembly language would still be chosen in the programming an embedded system even if it is sometimes used in conjunction with other languages such as C or C++ language. There are many factors why some programmers disagree with the use of assembly language in embedded system. One of the biggest factors is actually development time. Writing code in assembly language can sometime take much more and longer time than writing codes in a higher level language. Secondly, we talk about the maintainability of the use of assembly language , it is more difficult to modify and maintain because the language allows unstructured spaghetti code and all kinds of dirty tricks that are hard for others to actually fully understand the code. Moving on to portability, assembly code is very platform specific hence the porting to a different platform is very difficult. It is also known that assembly language has low reliability and security. It is easy to make errors, and the assembler is not checking if the calling conventions and register save conventions are obeyed. There are so many possibilities for hidden errors in assembly code that is affect the reliability and security of the system unless testing and verifying with a very systematic approach is done.

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Conclusion In conclusion, it can be easily said that assembly language clearly has more advantages than disadvantages when compared to most high-level programming languages. Firstly, because of its shortened mnemonic codes, it is more efficient as it is faster for a programmer to input codes which can save time, and offers the same flexibility as other programming languages. Assembly language can be used across almost all machines, if they have an interpreter to translate it into binary, and for machines that lack Operating systems. Another advantage is the ability to communicate easily and directly with hardware. Finally, assembly language can be enhanced for speed and accurate timing, and is interpreted quickly during processing. So, when compared with its disadvantages, it is clear that assembly language is the better and more favourable choice. To write great code requires one to write efficient code. Writing efficient code requires good algorithm choices and a good implementation of those algorithms. The best implementations are going to be written by those who've mastered assembly language or fully understand the low-level implementation of the high-level language statements they're choosing. This doesn't mean that we'll return to the days when major commercial applications were written entirely in assembly language. However, to reverse the trend of software running slower and slower even though CPUs are running faster and faster is going to require programmers to begin considering the low-level implications of the code that they write. So, even if you never intend to write a single line of assembly language code again, learning assembly language, and learning to think in assembly language, is one of the best things you can do to learn how to write better assembly code.

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References [9]. Aguiar, A. & Hessel, F. (2010). Embedded Systems Virtualization: The Next Challenge, IEEE International Symposium on Rapid System Prototyping, Source: http://www.inctsec.org/actrep/sites/default/files/highlights/GSE%20-%20Highlight%201%20and%20paper.pdf [12],[13]. Barr, M. (2007). Assembly vs. C, Source: http://www.barrgroup.com/EmbeddedSystems/How-To/Assembly-vs-C-Comparison [1]. Blum, R. (2005). Professional Assembly Language, Wiley Publishing Inc., ISBN: 0-7645-7901-0. [3],[14]. Ebrahim, A. (2010). Assembly Language and Embedded Systems Development, Source: http://mathscitech.orgarticlesassembly-value [2]. Fehnker, A. & Huuck, R. & Raunch, F., Seefried, S. (2008). Some Assembly Required – Program Analysis of Embedded System Code, Eighth IEEE International Working Conference on Source Code Analysis and Manipulation, IEEE Computer Society Australia. [11]. Linggesmeyer, P. & Trapp, M. (2009). Embedded Software: Trends in Embedded Software Engineering, IEEE Software Issue May/June 2009, Source: http://disciplinas.stoa.usp.br/pluginfile.php/28857/mod_resource/content/1/trends_in_embedded _software_engineering.pdf [7],[8],[10]. Moyer, B. (2013). Real World Multicore Embedded Systems, Newnes, Source: http://books.google.com.my/books?id=GSV6ho2zZUC&pg=PA290&lpg=PA290&dq=advantages+of+assembly+language+in+Embedded+systems&sou rce=bl&ots=HpecqjAjA1&sig=B_QpflOAau1AeKk657DF7vwdZI&hl=en&sa=X&ei=hdZqVMzaKcaQmwXNh4DIBg&ved=0CCcQ6AEwAjgU#v=onepage&q=advanta ges%20of%20assembly%20language%20in%20Embedded%20systems&f=false [4],[5]. Reddy, P. M. (2002). Embedded Systems, Resonance December 2002 Issue. [6]. Shibu, K. V. (2009). Introduction to Embedded Systems, Tata McGraw-Hill Education, Source: http://books.google.com.my/books?id=8hfn4gwR90MC&pg=PA378&lpg=PA378&dq=advantages+of +assembly+language+in+Embedded+systems&source=bl&ots=kItJac8ysq&sig=43AwesZHLaGq6kuA2S67cVf28s&hl=en&sa=X&ei=3dRqVNSwDivmAX91IK4Cw&ved=0CEIQ6AEwBTgK#v=onepage&q=advantages%20of%20assembly%20language% 20in%20Embedded%20systems&f=false

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