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Guillaume DERAMCHI edited this page Feb 22, 2024 · 3 revisions

mov instruction variants

The mov instruction is crucial for transferring data between registers, variables, and immediate values.

Register to immediate value

  • Syntax: mov rg2, 7
  • Binary Code: 0000 0010 0000 0111 (Op code: 0 0000)
  • Usage: Loads a number directly into a register.

Register to register

  • Syntax: mov rg2, rg7
  • Binary Code: 0001 1111 0000 1110, 0000 0010 0000 0000 (Op code: 0 0000)
  • Usage: Copies the value from one register to another.

Register to variable

  • Syntax: mov rg2, var2
  • Binary Code: 1011 1000 1101 0110 (var2 id), 0000 0010 0000 0000 (Op code: 0 0000)
  • Usage: Moves a variable's value into a register.

Variable to register

  • Syntax: mov var2, rg2
  • Binary Code: 0001 1010 0000 1110, 1100 0000 1101 0110 (var2 id) (Op code: 0 0000)
  • Usage: Stores a register's value into a variable.

Variable to variable

  • Syntax: mov var2, var1
  • Binary Code: 1011 1000 1101 0110 (var1 id), 1100 0000 1101 0110 (var2 id) (Op code: 0 0000)
  • Usage: Copies a value from one variable to another.

Variable to immediate value

  • Syntax: mov var2, 7
  • Binary Code: 1100 0000 1101 0110 (var2 id), 0000 0000 0000 0111 (Op code: 0 0000)
  • Usage: Assigns an immediate value to a variable.

mov instruction usage:

  • Loading an Immediate Value: 
    mov rg1, 5   ; Load 5 into register 1
  • Copying between registers: 
    mov rg2, rg1 ; Copy the value of rg1 to rg2
  • Variable manipulation: 
    mov rg3, varName  ; Move the value of varName into rg3
mov varName, rg3  ; Store the value of rg3 in varName

Stack operations in the Virtual Processor's assembly language are crucial for managing data in a Last-In-First-Out (LIFO) manner, particularly for subroutine calls and local variable storage. Additionally, the mov instruction is essential for various data transfer operations.

push and pop instructions

push

  • Syntax: push rgX
  • Function: Pushes the value in register rgX onto the stack.
  • Binary Code: Dependent on the specific register, e.g., 0010 0010 0000 0000 for push rg2.
  • Usage: Used for saving the current state of a register before modifying it or for preparing arguments for subroutine calls.

pop

  • Syntax: pop rgX
  • Function: Pops the top value from the stack into register rgX.
  • Binary Code: Based on the specific register, e.g., 0011 0010 0000 0000 for pop rg2.
  • Usage: Typically used to restore the value of a register or to retrieve subroutine call results.

pusha and popa instructions

pusha

  • Syntax: pusha
  • Function: Pushes the contents of all registers onto the stack.
  • Binary Code: 0001 1000 0000 1100 for the pusha instruction.
  • Usage: Used for saving the current state of all registers, typically at the beginning of a subroutine.

popa

  • Syntax: popa
  • Function: Pops values from the stack into all registers, except for register 3 which is read-only.
  • Binary Code: 0001 1000 0000 1101 for the popa instruction.
  • Usage: Used to restore the state of all registers, typically at the end of a subroutine.

Using pusha & popa:

  • Subroutine example: 
    subroutine:
    pusha               ; Push all register values onto the stack
    ; Perform various operations
    popa                ; Pop all register values back from the stack
    ret                 ; Return from the subroutine
main:
    call subroutine     ; Call the subroutine
    ; Execution continues here after the subroutine returns

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