Assembly Language -- Overview CISP 310 Prof. Chapman

CRC CISP 310Chapman Assembly Language Is… Not A High-Level Language

CRC CISP 310Chapman High-Level Languages (HLL) void main() { do something } *.c file Compiler not text, binary *.obj file not text, binary *.exe file Linker C library files (existing *.obj files)

CRC CISP 310Chapman High-Level Languages (HLL) C language program *.c file Programmer’s focus is on getting the syntax and structured logic correct in the source code

CRC CISP 310Chapman High-Level Languages C++ language program Object-oriented (OO) *.cpp file Programmer’s focus is on getting the syntax and OO logic correct

CRC CISP 310Chapman HLL Development Techniques Compiler catches syntax mistakes Compiler translates from text into processor-specific binary codes (object file)

CRC CISP 310Chapman HLL Development Techniques Memory for data storage and program code itself is automatically allocated Linker creates *.exe file

CRC CISP 310Chapman Assembly is Not a HLL An assembly programmer has to deal directly with the processor memory (RAM) The instructions are much more cryptic like “move data to a different memory address”

CRC CISP 310Chapman Assembly is Not a HLL We must write code to enable I/O between keyboard, files, and monitor (generally using operating system procedures) We must use a different design philosophy besides OO

CRC CISP 310Chapman Assembly is Not a HLL Loop and if logic is implemented differently in assembly than with HLL

CRC CISP 310Chapman HLL OO Procedure Let’s look at the code that defines the effect of clicking this Button control (VB.NET language)

CRC CISP 310Chapman ' called when Call Peedy button is clicked Private Sub btnCall_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCall.Click m_objMSpeaker.Show(0) ' move Peedy to a specified location m_objMSpeaker.MoveTo(Convert.ToInt16(Cursor.Position.X - 100), Convert.ToInt16(Cursor.Position.Y + 130)) m_objMSpeaker.Play("Wave") ' tell Peedy what to say m_objMSpeaker.Speak("Hello, I'm Peedy. Please say or select the name of the person whose phone number you would like to find.", "") m_objMSpeaker.Speak("If you wish to say the name, press the Scroll Lock key then speak the name.", "") m_objMSpeaker.Play("RestPose") cboName.Enabled = True btnCall.Enabled = False End Sub ' btnCall_Click HLL comment subroutine with 7 HLL statements

CRC CISP 310Chapman HLL Translated Into Assembly Every high-level instruction is equivalent to a group of many assembly instructions Each assembly instruction is cryptic

CRC CISP 310Chapman m_objMSpeaker.Speak("Hello, I'm Peedy. Please say or select the name of the person whose phone number you would like to find.", "") This HLL statement Eight Assembly statements f5 mov esi,dword ptr [ebx ECh] fb push dword ptr ds:[ h] mov ecx,esi mov edx,dword ptr ds:[020529C4h] mov eax,dword ptr [ecx] b mov eax,dword ptr [eax+0Ch] e mov eax,dword ptr [eax ACh] call dword ptr [eax+5Ch] =

CRC CISP 310Chapman Assembly Sample Assembly Instruction f5 mov esi,dword ptr [ebx ECh] operation code operands register (memory) hexadecimal constant

CRC CISP 310Chapman Assembly Language Is… Not Self-Documenting

CRC CISP 310Chapman What Does This Accomplish? f5 mov esi,dword ptr [ebx ECh] fb push dword ptr ds:[ h] mov ecx,esi mov edx,dword ptr ds:[020529C4h] mov eax,dword ptr [ecx] b mov eax,dword ptr [eax+0Ch] e mov eax,dword ptr [eax ACh] call dword ptr [eax+5Ch] nop Huh?

CRC CISP 310Chapman What’s Difficult About Assembly? Cannot easily see purpose of code segment (see previous slide) Not portable (separate assembly instructions for Intel, Motorola, … processors)

CRC CISP 310Chapman What’s Right With Assembly? Every language is based on machine code, and assembly is closest to machine code Assembly is necessary to write high-level language translators Java/C++/C#/VB.NET/Fortran/…)

CRC CISP 310Chapman What’s Right With Assembly? We can write I/O code to communicate between our program and peripherals (cameras, iPods, etc.) We can write instructions that are optimized for our processor, creating very very small and very very fast programs

CRC CISP 310Chapman What You Will Learn At the end of this course, you will be able to create simple command-line programs that accept input from the keyboard and display text output to the monitor You will finally understand the structure of memory and the inner workings of the processor chip

CRC CISP 310Chapman Ending Metaphor HLL programmers: authors who develop the content of a book but leave the details of typesetting, printing, sales, and distribution to someone else Assembly programmers: authors who can both write and publish, sell, and distribute their own books. They understand programming at a deeper level than a HLL programmer.