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Home , Assembly language

COSC2200: Hardware Systems Introduction to and MIPS ISA

Instructor: Rong Ge

Extracted from various online sources

1 Outline

• Why do we learn programing? • Format of assembly programs • MIPS Instruction Set Architecture

2 Programming on Early

• Wire the circuits to solve the desired problem – No program instructions, no memory • Load instructions manually, one at a time, to stored-program computer – Machine instructions

• Programming needed to be easier

• The first programming support programs were assembers

3 Assemblers

• Assemblers allow the to use simple names for instructions in writing a program – “Add”, for example – The program is constructed using instruction acronyms. – The assembler converted the English test names to the combinations of 1’s and 0’s that represented instructions. – Automatic program loading was developed with tapes and disks • Today, most time we program in high level language because – arrived

4 A Translation Hierarchy , , and some other HLL

• High Level Language (HLL) programs first compiled (possibly into assembly), Assembly language program then linked and finally loaded into main memory.

Assembler

Object: Machine language module Object: routine (machine language)

Linker

Executable: Machine language program

Loader

Memory

5 Why Learn Assembly Language

• Compilers reduce the “feel” of the -hardware interaction. – HLL code uses keywords, libraries, – Remove the lower-level visibility of computer and program operation • Assembly language programming gives the “feel” of computer operation – Assembly language is machine specific and “low level” – The program and syntax is much closer to the computer’s processor, memory, and I/O system • Learning assembly language also helps in understanding much of the of computer design • Some programs still need assembly language for – Direct hardware manipulation – Access to specialized processor instruction, or performance

6 Assembly Program Template

# Title: Filename: # Author: Date: # Description: # Input: # Output: ################# segment ##################### .data . . . ################# Code segment ##################### .text .globl main main: # main program entry . . . li v0, 10 # load an immediate # program Assembly Language Statements

• One statement should appear on a line • Three types of statement: Instructions – Generate for the processor to execute at runtime – Instructions tell the processor what to do Pseudo-Instructions and Macros – Translated by the assembler into real instructions – Simplify the task Assembler Directives – Provide information to the assembler while translating a program – Used to define segments, allocate memory variables, etc. – Non-executable: directives are not part of the instruction set .DATA, .TEXT, & .GLOBL Directives • .DATA – Defines the data segment of a program containing data – The program's variables should be defined under this directive – Assembler will allocate and initialize the storage of variables • .TEXT directive – Defines the code segment of a program containing instructions • .GLOBL directive – Declares a symbol as global – Global symbols can be referenced from other files – We use this directive to declare main procedure of a program Instructions

• Assembly language instructions have the format: [:] mnemonic [] [#comment] • Label: (optional) – Marks the address of a memory location, must have a colon – Typically appear in data and text segments • Mnemonic – Identifies the operation (e.g. add, sub, etc.) • Operands – Specify the data required by the operation – Operands can be registers, memory variables, or constants – Most instructions have three operands L1: addiu t0, t0, 1 #increment the value in t0 Comments

• Comments are very important!

– Explain the program's purpose

– When it was written, revised, and by whom

– Explain data used in the program, input, and output

– Explain instruction sequences and used

– Comments are also required at the beginning of every procedure

• Indicate input parameters and results of a procedure

• Describe what the procedure does

• Single-line comment – Begins with a pound sign # and terminates at end of line Structure of Conventional Processor

• ALU: Arithmetic and Logic Unit • Local storage • Controller • Internal DataPath • External interface Parts of A Conventional Processor

• Arithmetic Logic Unit (ALU) Can perform operations – Integer arithmetic: addition, subtraction, multiplication, divide – binary AND, OR, NOT, XOR, etc. – Shift (left, right, circular) • Local Storage – Registers – Typical modern processors have 8 to 32 regs, 32 to 64 Parts of A Conventional Processor

• Controller – tells ALU which operation to perform next, and local storage which (s) to provide and where to store result – Executes program • Could be hardwired for simple procs • Could be fetching next line of program from main memory • Internal data path – Has to be "wide" enough to move entire registers quickly. – Multiple of register size • External interface – external to processor, not computer – Connects to external, main memory (RAM) Instruction Set Architecture (ISA)

• ISA: the part of the processor that is visible to the programmer or compiler writer – Serves the boundary between software and hardware • The ISA of a processor can be described using 5 categories – Operand storage in the CPU • Where are the operands kept other than in memory? – Number of explicit named operands • How many operands are named in a typical instruction? – Operand location • Can any ALU instruction operand be located in memory? – Operations • What operations are provided in the ISA – Type and size of operands • What is the type and size of each operand and how is it specified?

15 MIPS Instruction Set Architecture

° Instruction Categories . Load/Store . Computational . Jump and Branch . Floating Point (coprocessor) 3 Instruction Formats: all 32 bits wide ALU () instructions have 3 operands which are only registers The only memory access is through explicit load/store instructions

R OP Rs Rt Rd sa funct I OP Rs Rt Immediate J OP jump target 32 registers Number: $0 $1 $2-$3 $4-$7 Name: zero at v0-v1 a0-a3

$8-$15 $16-$23 $23-$31

t0-t7 s0-s7 8 other registers not discussed here 16