LANGUAGE OF THE COMPUTERS

Machine Language vs Assembly Language

machine instruction statement	assembly language
0000 0001 0010 1011 1000 0000 0010 0000	add $t0,$t1,$t2

The instruction means: 

• add the integers in registers $t1 and $t2 and put the result in register $t0.
  
  
• Assembly language —(assembler)—> Machine language
                           translator

 Instruction Set

• Instructions are the language of the machine
  
  Instructions Set Architecture (ISA)
• Defines a "family" of microprocessors
• Examples: Intel x86 (IA32), Sun Sparc, DEC Alpha, IBM/360, IBM PowerPC, M68K, DEC VAX
•  ISA includes:
  ◦Instruction set
  ◦Rules for using instructions --> Mnemonics, functionality, addressing modes
  ◦Instruction encoding
  
  The Organization of A Computer
  
  

  • There are five basic components:
    1. Input - devices that writes data to memory
    2. Output - devices that read data from memory and convey result of the computation
    3. Datapath (ALU) - performs arithmetic operations
    4. Memory - the storage area (keeping data that are needed by the running programs)
    5. Control - the component of a processor that sends the signals which determine the operations of the datapath,memory,input and output
       by : Nor Izzati
       
       
       
       

  Microprocessor Operations
  The process of processor completing three basic steps to execute one machine instruction is called machine cycle
  
  
  

   
  A machine cycle
  
  Microprocessor without Interlocked Pipelines Stages (MIPS)
  
  
  MIPS is a reduced instruction set computer (RISC) instruction set architecture
  

  
  
  

  Register

  • 32 general-purpose registers
  • register preceded by $ in assembly language instruction two formats for addressing:
    --> using register number e.g $0 through $31
    --> using equivalent names e.g $t1,$sp
  • special registers Lo and Hi used to store result of multiplication and division
    -->  not directly addressable; contents accessed with special mfhi ("move from Hi") and mflo
           ("move from Lo")
  • stack grows from high memory to low memory

  • Register Number	Alternative Name	Description
    0	zero	the value 0
    1	$at	(assembler temporary) reserved by the assembler
    2-3	$v0 - $v1	(values) from expression evaluation and function results
    4-7	$a0 - $a3	(arguments) First four parameters for subroutine. Not preserved across procedure calls
    8-15	$t0 - $t7	(temporaries) Caller saved if needed. Subroutines can use w/out saving. Not preserved across procedure calls
    16-23	$s0 - $s7	(saved values) - Callee saved. A subroutine using one of these must save original and restore it before exiting. Preserved across procedure calls
    24-25	$t8 - $t9	(temporaries) Caller saved if needed. Subroutines can use w/out saving. These are in addition to $t0 - $t7 above. Not preserved across procedure calls.
    26-27	$k0 - $k1	reserved for use by the interrupt/trap handler
    28	$gp	global pointer. Points to the middle of the 64K block of memory in the static data segment.
    29	$sp	stack pointer Points to last location on the stack.
    30	$s8/$fp	saved value / frame pointer Preserved across procedure calls
    31	$ra	return address

                                This is from Figure 9.9 in the Goodman&Miller text
    
    
    System Calls
    

    • used to read or print values or strings from input/output window, and indicate program end 
    •  use syscall operating system routine call 
    •  first supply appropriate values in registers $v0 and $a0-$a1 
    •  result value (if any) returned in register $v0
                                          System call functions
    

    Service	Code in $v0	Arguments	Results
    print_int	1	$a0 = integer to be printed
    print_float	2	$f12 = float to be printed
    print_double	3	$f12 = double to be printed
    print_string	4	$a0 = address of string in memory
    read_int	5		integer returned in $v0
    read_float	6		float returned in $v0
    read_double	7		double returned in $v0
    read_string	8	$a0 = memory address of string input buffer $a1 = length of string buffer (n)
    sbrk	9	$a0 = amount	address in $v0
    exit	10

    
    

Program Structure

• just plain text file with data declarations, program code (name of file should end in suffix .s to be used with SPIM simulator) 
•  data declaration section followed by program code section 
• have a format that comprises of four columns: