Assembly Variables : Registers and Arithmetic Operations

Assembly Variables : Registers

Unlike high level language like C++ or Java,assembly cannot use variable because to keep hardware simple.

- Assembly Operands are Registers
                - Limited number of special locations built directly into the hardware.
                - Operation can only be performed on Registers.

- Benefit
                1) Since registers are directly in hardware,they are very fast(faster than 1 bilionth of a
                      second).

- Drawback
                1) Since registers are in hardware,there are a predetermined number of them.
                               - Solution : MIPS code must be very carefully put together to efficiently use                                                             registers.

- There are 32 registers in MIPS,because smaller is faster.Each MIPS registers is 32 bits wide.Groups          of 32 bits called a word in MIPS.

Arithmetic Operations

- Add and subtract, three operands.
                - Two sources and one destinations.

- All arithmetic operations have this form

- Design Principle 1 : Simplicity Favours regularity
                1) Regularity makes implementation simpler.
                2) Simplicity enables higher performance at lower cost.

- Registers are numbered from 0 to 31

- Each register can be referred to by number or name.

- $0,$1,$2….until $31

- By convention,each register also has a name to make it easier to code.

- In Assembly Language, The register have no type.Operation determines how register contents are treated.

- Comments in assembly,hash(#) is used for MIPS comments
                1) anything from hash mark to end of line is a comment an will be ignored.

- In assembly language,each statement, excutes exactly one of a short list of simple commands.

MIPS Addition and Subtraction

- Syntax of Instructions:

1  2,3,4

where :

1) Operation by name.
2)Operand getting result(destination).
3)1^st Operand for operation(source 1).
4) 2^nd Operand for operation(soruce 2).

- Syntax is rigid
                1) 1 operator , 3 operands.
                2) Because to keep hardware simple via regularity.

- Addition in Assembly
                1) example: add  $s0, $s1, $s2(in MIPS).
                2) Equivalent to: a = b + c(in C).
                3)Where MIPS registers $s0, $s1, $s2 are associated with C variables a,b,c.

- Subtraction in Assembly
                1) example: sub  $s3, $s4, $s5(in MIPS).
                2) Equivalent to: d = e - f(in C).
                3)Where MIPS registers $s3, $s4, $s5 are associated with C variables d,e,f.

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Language of the Computer

Introduction

- Assembly Language

The basic job of a CPU,its excute lots of instructions.The set of instructions a particular CPU implements is an Instruction Set Architecture (ISA),few examples:

1) Intel 80x86 (Pentium 4)
2)IBM/Motorola
3)PowerPc (old Macintosh)
4)MIPs
5)Intel IA64

Different CPU implement different sets of instructions.More primitive than higher level languages.No sophisticated control flow such as while for loops.their design goals is maximize performance and minimize cost and reduce design time.

- Instrunction Set Architectures

ISA includes:
                1) instructions set.
                2) Rules for using instructions:
                               - Mnemonics,functionality,addressing modes.
                3) Instruction encoding.

Early trend(instructions) was to add more and more instructions to new CPU to do elaborate operations.Early trend is like “Add more To work more”
                - VAX architecture had an instruction to multiply polynomials.

RISC Philosophy (Cocke IBM ,Patterson,Hennessy,1980s)
                - Keep the instruction set small and simple,makes it eiser to build fast hardware.
                - Let software do complicated operations b composing simpler ones.

New trend is like “Less instruction But more task”

- MIPS Architecture

MIPS – semiconductor company that built one of the first commercial RISC architecture.
People choose MIPS instead of intel 80x86 because:
                - MIPS is simple,elegant.Don’t want to get bogged down in gritty details.
                - MIPS widely used in embedded apps,x86 little used in embedded, and more                                          embedded computers than PCs.

- SPIM : the MIPS simulator

SPIM (MIPS spelt backwards!) is a MIPS simulator that :
                - reads MIPS assembly language files and translates to machine
                 Language
                - executes the machine language instruction
                - shows contents of registers and memory
                - works as a debugger (supports break-points and single-stepping)
                - provides basic OS-like services, like simple I/O

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MIPS SIMULATOR : The SPIM operating system

   The SPIM simulator comes with a rudimentary operating system, which allows the programmer usage of common used functions in a comfortable way. Such functions are invoked by the syscall-instruction. Then the OS acts depending on the values of specific registers

.

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MIPS SIMULATOR : Type of Simulator

TYPE OF MIPS SIMULATOR 

QTSPIM

The newest version of Spim is called QtSpim, and unlike all of the other version, it runs on Microsoft Windows, Mac OS X, and Linux the same source code and the same user interface on all three platforms! QtSpim is the version of Spim that currently being actively maintaned. The other versions are still available, but please stop using them and move to QtSpim. It has a modern user interface, extensive help, and is consistent across all three platforms. 

QtSpim makes my life far easier, and will likely improve yours and your students' experience as well. A compiled, immediately installable version of QtSpim is available for Microsoft Windows, Mac OS X, and Linux can be downloaded from:  https://sourceforge.net/projects/spimsimulator/files/.

GXemul (formerly known as mips64emul) is a computer architecture emulator being developed by Anders Gavare. It is available as free software under a revised BSD-style license. In 2005, Gavare changed the name of the software project from mips64emul to GXemul. This was to avoid giving the impression that the emulator was confined to the MIPS instruction set, which was the only architecture being emulated initially.

Although development of the emulator is still a work-in-progress, since 2004 it has been stable enough to let various unmodified guest operating systems run as if they were running on real hardware. Currently emulated processor architectures include ARM, MIPS, M88K, PowerPC, and SuperH. Guest operating systems that have been verified to work inside the emulator are NetBSD, OpenBSD, Linux, HelenOS, Ultrix, and Sprite.

Apart from running entire guest operating systems, the emulator can also be used for experiments on a smaller scale, such as hobby operating system development, or it can be used as a general debugger.

MARS (MIPS Assembler and Runtime      Simulator)

MARS is a lightweight interactive development environment (IDE) for programming in MIPS assembly language, intended for educational-level use with Patterson and Hennessy's Computer Organization and Design.It was developed by Pete Sanderson and Kenneth Vollmar at Missouri State University.

       QEMU (short for Quick Emulator)

It is a free and open-source hosted hypervisor that performs hardware virtualization (not to be confused with hardware-assisted virtualization).QEMU is a generic and open source machine emulator and virtualizer. When used as a machine emulator, QEMU can run OSes and programs made for one machine (e.g. an ARM board) on a different machine (e.g. your own PC). By using dynamic translation, it achieves very good performance.

QEMU is a hosted virtual machine monitor: It emulates CPUs through dynamic binary translation and provides a set of device models, enabling it to run a variety of unmodified guest operating systems. It also can be used together with KVM in order to run virtual machines at near-native speed (requiring hardware virtualization extensions on x86 machines). QEMU can also be used purely for CPU emulation for user-level processes, allowing applications compiled for one architecture to be run on another..

  

MIP SIMULATOR ONLINE

             MIPhpS: Online MIPS Simulator v0.10

Please enter MIPS binary below. It should include address-instruction pairs in hexadecimal, formatted with a colon between the address and the data (instruction)

link mip simulator online : https://alanhogan.com/asu/assembler.php

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MIPS Simulator (Introduction)

SPIM is a MIPS processor simulator, designed to run assembly language code for this architecture. The program simulates R2000 and R3000 processors, and was written by James R. Larus while a professor at the University of Wisconsin-Madison.[2] The MIPS machine language is often taught in college-level assembly courses, especially those using the textbook Computer Organization and Design: The Hardware/Software Interface by David A. Patterson and John L. Hennessy (ISBN 1-55860-428-6).

The name of the simulator is a reversal of the letters "MIPS".

SPIM simulators are available for Windows (PCSpim), Mac OS X and Unix/Linux-based (xspim) operating systems. As of release 8.0 in January 2010, the simulator is licensed under the standard BSD license.

In January, 2011, a major release version 9.0 features QtSpim that has a new user interface built on the cross-platform Qt UI framework and runs on Windows, GNU/Linux, and Mac OS X. From this version, the project has also been moved to SourceForge for better maintenance. Precompiled versions of QtSpim for Linux (32-bit), Windows, and Mac OS X, as well as PCSpim for Windows are provided.

 Figure 1

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Introduction To Computer

Introduction To Computer

A computer is a multipurpose electronic device that can receive, process and store data. They are used as tools in every part of society together with the Internet. Computers nowadays are complex; there are a lot of different components inside them, and they all serve different purposes. They all need to work together for the computer to work; knowing how a computer works makes it easier to use a computer by being able to understand how a computer will respond.

What Is Computer?

A computer is an electronic device that takes input such as numbers, text, sound, image, animations, video, etc., processes it, and converts it into meaningful information that could be understood, presenting the changed input (processed input) as output. All numbers, text, sound, images, animations, and video used as input are called data, and all numbers, text, sound, images, animations, and video returned as output are called information. Input is the raw data entered into the computer by using input devices.
The data consists of numbers, text, sound, images, animations, and video.
The process converts numbers, text, sound, images, animations, and video (data) into usable data, which is called information.
The information consists of numbers, text, sound, images, animations, and video that has been converted by the process.
The data is inserted using an input device.
The central processing unit (CPU) converts data to information.
The information is put on an output device.


A storage device is an apparatus for storing data and information. A basic computer consists of 4 components: an input device , a CPU, output devices, and memory.

MONITOR







KEYBOARD










CPU CASING















SPEAKER







MOUSE

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Digital Logic-Logic Gates

Logic Gates

If we think of two signals, A and B, as representing a truth value of two different propositions, then A could be either TRUE (a logical 1) or FALSE (a logical 0). B can take on the same values. Now consider a situation in which the output, C, is TRUE only when both A is TRUE and B is TRUE. We can construct a truth table for this situation. In that truth table, we insert all of the possible combinations of inputs, A and B, and for every combination of A and B we list the output, C.
 

A	B	C
False	False	False
False	True	False
True	False	False
True	True	True

An AND Example

Let's imagine a physician prescribing two drugs. For some conditions drug A is prescribed, and for other conditions drug B is prescribed. Taken separately each drug is safe. When used together dangerous side effects are produced.

Let
A = Truth of the statement "Drug 'A' is prescribed.".
B = Truth of the statement "Drug 'B' is prescribed.".
C = Truth of the statement "The patient is in danger.".

Then, the truth table below shows when the patient is in danger.

 

A	B	C
False	False	False
False	True	False
True	False	False
True	True	True

Notice that C is TRUE when both A AND B are true and only then!

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AND GATES

An AND function can be implemented electrically using a device known as an AND gate. You might imagine a system in which zero (0) is represented by zero (0) volts, and one (1) is represented by three (3) volts, for example. If we are going to use electrical devices we need some sort of symbolic representation. There is a standard symbol for an AND gate shown below.





Often in lab work it's helpful to use an LED to show when a signal is 0 or 1. Usually a 1 is indicated with an LED that is ON (i.e. glowing). You can use the buttons below to check out this AND gate (Note what an AND gate symbol looks like!) with a simulated LED. Note the following in the simulation (and you can use this in your lab experiments).


To get a logical zero, connect the input of the gate to ground to have zero (0) volts input.
To get a logical one, connect the input of the gate to a five (5) volts source to have five volts at the input.
Each button controls one switch (two buttons - two switches) so that you can control the individual inputs to the gate.
Each time you click a button, you toggle the switch to the opposite position.

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        Once we introduce Boolean variables, we can rethink the concept of a truth table. In the truth table below, if A, B and C are truth tables and we have an AND gate with A and B as inputs and C as the output, the truth table would look like this.

A	B	C
0	0	0
0	1	0
1	0	0
1	1	1

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OR Gates

Consider a case where a pressure can be high and a temperature can be high Let's assume we have two sensors that measure temperature and pressure.. The first sensor has an output, T, that is 1 when a temperature in a boiler is too high, and 0 otherwise. The second sensor produces an output, P, that is 1 when the pressure is too high, and 0otherwise. Now, for the boiler, we have a dangerous situation when either the temperature or the pressure is too high. It only takes one. Let's construct a truth table for this situation. The output, D, is 1 when danger exists.   
 

T	P	D
False	False	False
False	True	True
True	False	True
True	True	True

        

What we have done is defined an OR gate. An OR gate is a gate for which the output is 1 whenever one or more of the inputs is 1. The output of an OR gate is 0 only when all inputs are 0. Shown below is a schematic symbol for an OR gate, together with the simulated LEDs and input buttons so that you can explore OR gate behavior.



In terms of Boolean variables, the truth table for an OR gate looks like this.
  
 

A	B	C
0	0	0
0	1	1
1	0	1
1	1	1

NOT Gates (Inverters)

A third important logical element is the inverter. An inverter does pretty much what it says. If the input is 0, the output is 1. Conversely, if the input is 1, the output is 0. The symbol for an inverter is shown below. Again, you can putter with this inverter with the simulated LEDs. X is the input to the inverter. The output is NOT-X represented as ~1 or:

The truth table for an inverter is pretty simple since there is only one input. Call the input A, and the output C, and the truth table is:

A	C
0	1
1	0

NAND Gates

        

There is another important kind of gate, the NAND gate. Actually, the way to start thinking about a NAND gate is to think of it as an AND gate with an inverter on the output. That's shown below.





Actually, however, the symbol for a NAND gate compresses the inverter down to a dot at the output of the NAND gate as shown below.

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