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ASSEMBLY LANGUAGE BOOK

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Assembly Language Book

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PDF Drive is your search engine for PDF files. As of today we have 78,, eBooks for you to download for free. No annoying ads, no download limits, enjoy . I taught Computer Science at the University of Central Oklahoma for 10 years. During this time I taught an introductory course in PC Assembly Language. Other PC assembly language books still teach how to program the processor that the original PC used in. ! The processor only.

Why Assembly Language?

The author had, however, chosen a small, well-defined assembly-language routine to refine, consisting of about 30 instructions that did nothing more than expand 8 bits to 16 bits by duplicating each bit. In short, he had used all the information at his disposal to improve his code, and had, as a result, saved cycles by the bushel.

There was, in fact, only one slight problem with the optimized version of the routine… It ran slower than the original version! As diligent as the author had been, he had nonetheless committed a cardinal sin of assembly-language programming: he had assumed that the information available to him was both correct and complete.

While the execution times provided by Intel for its processors are indeed correct, they are incomplete; the other — and often more important — part of code performance is instruction fetch time, a topic to which I will return in later chapters.

Assume nothing. I cannot emphasize this strongly enough — when you care about performance, do your best to improve the code and then measure the improvement. Ignorance about true performance can be costly. When I wrote video games for a living, I spent days at a time trying to wring more performance from my graphics drivers.

I rewrote whole sections of code just to save a few cycles, juggled registers, and relied heavily on blurry-fast register-to-register shifts and adds.

As I was writing my last game, I discovered that the program ran perceptibly faster if I used look-up tables instead of shifts and adds for my calculations. In truth, instruction fetching was rearing its head again, as it often does when programming the , and the fetching of the shifts and adds was taking as much as four times the nominal execution time of those instructions. Ignorance can also be responsible for considerable wasted effort.

The letter writers counted every cycle in their timing loops, just as the author in the story that started this chapter had. Like that author, the letter writers had failed to take the prefetch queue into account. In fact, they had neglected the effects of video wait states as well, so the code they discussed was actually much slower than their estimates. The proper test would, of course, have been to run the code to see if snow resulted, since the only true measure of code performance is observing it in action.

The Zen Timer One key to mastering the Zen of assembler is clearly a tool with which to measure code performance. The can be started at the beginning of a block of code of interest and stopped at the end of that code, with the resulting count indicating how long the code took to execute with an accuracy of about 1 microsecond.

A microsecond is one -millionth of a second, and is abbreviated us. To be precise, the counts once every A nanosecond is one-billionth of a second, and is abbreviated ns. On the other hand, it is by no means essential that you understand exactly how the Zen timer works. Interesting, yes; essential, no. Instead, focus on learning how to use the timer, since we will use it heavily throughout The Zen of Assembly Language.

ZTimerOn saves the context of the calling code, disables interrupts, sets timer 0 of the to mode 2 divide-by-N mode , sets the initial timer count to 0, restores the context of the calling code, and returns.

Two aspects of ZTimerOn are worth discussing further. One point of interest is that ZTimerOn disables interrupts. Were interrupts not disabled by ZTimerOn, keyboard, mouse, timer, and other interrupts could occur during the timing interval, and the time required to service those interrupts would incorrectly and erratically appear to be part of the execution time of the code being measured.

As a result, code timed with the Zen timer should not expect any hardware interrupts to occur during the interval between any call to ZTimerOn and the corresponding call to ZTimerOff, and should not enable interrupts during that time. Time and the PC A second interesting point about ZTimerOn is that it may introduce some small inaccuracy into the system clock time whenever it is called.

Assembly Language Books

The actually contains three timers, as shown in Figure 2. Each of the three timers counts down in a programmable way, generating a signal on its output pin when it counts down to 0. Timer 2 drives the speaker, although it can be used for other timing purposes when the speaker is not in use. As shown in Figure 2. On the other hand, the output of timer 2 is connected to nothing other than the speaker. Timer 1 is dedicated to providing dynamic RAM refresh, and should not be tampered with lest system crashes result.

Finally, timer 0 is used to drive the system clock. A millisecond is one-thousandth of a second, and is abbreviated ms. This line is connected to the hardware interrupt 0 IRQ0 line on the system board, so every Each timer channel of the can operate in any of 6 modes.

Timer 0 normally operates in mode 3, square wave mode. In square wave mode, the initial count is counted down two at a time; when the count reaches zero, the output state is changed.

The initial count is again counted down two at a time, and the output state is toggled back when the count reaches zero. The result is a square wave that changes state more slowly than the input clock by a factor of the initial count. In its normal mode of operation, timer 0 generates an output pulse that is low for about Square wave mode is not very useful for precision timing because it counts down by 2 twice per timer interrupt, thereby rendering exact timings impossible.

Fortunately, the offers another timer mode, mode 2 divide-by-N mode , which is both a good substitute for square wave mode and a perfect mode for precision timing. Divide-by-N mode counts down by 1 from the initial count.

When the count reaches zero, the timer turns over and starts counting down again without stopping, and a pulse is generated for a single clock period. As a result, timer 0 continues to generate timer interrupts in divide-by-N mode, and the system clock continues to maintain good time.

Why not use timer 2 instead of timer 0 for precision timing?

We need the interrupt generated by the output of timer 0 to tell us when the count has overflowed, and we will see shortly that the timer interrupt also makes it possible to time much longer periods than the Zen timer shown in Listing supports.

In fact, the Zen timer shown in Listing can only time intervals of up to about 54 ms in length, since that is the period of time that can be measured by timer 0 before its count turns over and repeats. If a measured period turns out to be longer than 54 ms that is, if timer 0 has counted down and turned over , the Zen timer will display a message to that effect.

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A long-period Zen timer for use in such cases will be presented later in this chapter. The Zen timer determines whether timer 0 has turned over by checking to see whether an IRQ0 interrupt is pending. Remember, interrupts are off while the Zen timer runs, so the timer interrupt cannot be recognized until the Zen timer stops and enables interrupts. If an IRQ0 interrupt is pending, then timer 0 has turned over and generated a timer interrupt.

Recall that ZTimerOn initially sets timer 0 to 0, in order to allow for the longest possible period — about 54 ms — before timer 0 reaches 0 and generates the timer interrupt. Since timer 0 is initially set to 0 by the Zen timer, and since the system clock ticks only when timer 0 counts off In addition, a timer interrupt is generated when timer 0 is switched from mode 3 to mode 2, advancing the system clock by up to Finally, up to Net result: the system clock will run up to ms about a ninth of a second slow each time the Zen timer is used.

Potentially far greater inaccuracy can be incurred by timing code that takes longer than about ms to execute. Recall that all interrupts, including the timer interrupt, are disabled while timing code with the Zen timer. Assembly language is infrequently used by programmers nowadays, but there are still good reasons to learn the language.

All Assembly Languages

It is the most powerful computer programming language available. While assembly language shares very little with high level languages such as Java, C , Python etc , and assembly languages for different CPU architectures often have little in common, it gives programmers the insight required to write effective code in high-level languages.

Assembly language is also used primarily for direct hardware manipulation, access to specialized processor instructions, or to address critical performance issues. Assembly is excellent for speed optimization. We have published a series covering the best open source programming books for other popular languages.

Read them here. The Art of Assembly Language Programming. Toggle navigation FreeTechBooks. Assembly A low-level language used in the writing of computer programs. All categories Follow Books under this sub-category 13 books. Assembly Language Programming Post date: Publication date: Assemblers And Loaders Post date: It is not concerned with any specific assembler language.

Ellis Horwood Ltd Publication date: How to Optimize for the Pentium Microprocessors Post date: It covers basic operators and instructions, subprogram calling, loading and storing memory, program control, and the conversion of the assembly language program into machine code. The Cupola Scholarship Publication date:This book has been designed as a complete self-contained text for learning programming, using the Z Exploring C, x86 Assembly, and Machine Code This book is intended to increase the reader's understanding of the relationship between x86 machine code, x86 Assembly Language, and the C Programming Language.

On the other hand, the output of timer 2 is connected to nothing other than the speaker.

Ellis Horwood Ltd Publication date: Randall Hyde. Programming the

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