Package mars.simulator

Class BackStepper

java.lang.Object
mars.simulator.BackStepper
public class BackStepper extends Object
Used to "step backward" through execution, undoing each instruction.
Version:
February 2006
Author:
Pete Sanderson

  • Constructor Summary

    Constructors
    Constructor
    Description
    BackStepper()
    Create a fresh BackStepper.

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    addConditionFlagClear​(int flag)
    Add a new "back step" (the undo action) to the stack.
    int
    addConditionFlagSet​(int flag)
    Add a new "back step" (the undo action) to the stack.
    int
    addCoprocessor0Restore​(int register, int value)
    Add a new "back step" (the undo action) to the stack.
    int
    addCoprocessor1Restore​(int register, int value)
    Add a new "back step" (the undo action) to the stack.
    int
    addDoNothing​(int pc)
    Add a new "back step" (the undo action) to the stack.
    int
    addMemoryRestoreByte​(int address, int value)
    Add a new "back step" (the undo action) to the stack.
    int
    addMemoryRestoreHalf​(int address, int value)
    Add a new "back step" (the undo action) to the stack.
    int
    addMemoryRestoreRawWord​(int address, int value)
    Add a new "back step" (the undo action) to the stack.
    int
    addMemoryRestoreWord​(int address, int value)
    Add a new "back step" (the undo action) to the stack.
    int
    addPCRestore​(int value)
    Add a new "back step" (the undo action) to the stack.
    int
    addRegisterFileRestore​(int register, int value)
    Add a new "back step" (the undo action) to the stack.
    void
    backStep()
    Carry out a "back step", which will undo the latest execution step.
    boolean
    empty()
    Check whether there are steps that can be undone.
    boolean
    enabled()
    Determine whether execution "undo" steps are currently being recorded.
    boolean
    inDelaySlot()
    Determine whether the next back-step action occurred as the result of an instruction that executed in the "delay slot" of a delayed branch.
    void
    setEnabled​(boolean state)
    Set enable status.

    Methods inherited from class java.lang.Object

    equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • BackStepper

      public BackStepper()
      Create a fresh BackStepper. It is enabled, which means all subsequent instruction executions will have their "undo" action recorded here.

  • Method Details

    • enabled

      public boolean enabled()
      Determine whether execution "undo" steps are currently being recorded.
      Returns:
      true if undo steps being recorded, false if not.

    • setEnabled

      public void setEnabled​(boolean state)
      Set enable status.
      Parameters:
      state - If true, will begin (or continue) recoding "undo" steps. If false, will stop.

    • empty

      public boolean empty()
      Check whether there are steps that can be undone.
      Returns:
      true if there are no steps to be undone, false otherwise.

    • inDelaySlot

      public boolean inDelaySlot()
      Determine whether the next back-step action occurred as the result of an instruction that executed in the "delay slot" of a delayed branch.
      Returns:
      true if next backstep is instruction that executed in delay slot, false otherwise.

    • backStep

      public void backStep()
      Carry out a "back step", which will undo the latest execution step. Does nothing if backstepping not enabled or if there are no steps to undo.

    • addMemoryRestoreRawWord

      public int addMemoryRestoreRawWord​(int address, int value)
      Add a new "back step" (the undo action) to the stack. The action here is to restore a raw memory word value (setRawWord).
      Parameters:
      address - The affected memory address.
      value - The "restore" value to be stored there.
      Returns:
      the argument value

    • addMemoryRestoreWord

      public int addMemoryRestoreWord​(int address, int value)
      Add a new "back step" (the undo action) to the stack. The action here is to restore a memory word value.
      Parameters:
      address - The affected memory address.
      value - The "restore" value to be stored there.
      Returns:
      the argument value

    • addMemoryRestoreHalf

      public int addMemoryRestoreHalf​(int address, int value)
      Add a new "back step" (the undo action) to the stack. The action here is to restore a memory half-word value.
      Parameters:
      address - The affected memory address.
      value - The "restore" value to be stored there, in low order half.
      Returns:
      the argument value

    • addMemoryRestoreByte

      public int addMemoryRestoreByte​(int address, int value)
      Add a new "back step" (the undo action) to the stack. The action here is to restore a memory byte value.
      Parameters:
      address - The affected memory address.
      value - The "restore" value to be stored there, in low order byte.
      Returns:
      the argument value

    • addRegisterFileRestore

      public int addRegisterFileRestore​(int register, int value)
      Add a new "back step" (the undo action) to the stack. The action here is to restore a register file register value.
      Parameters:
      register - The affected register number.
      value - The "restore" value to be stored there.
      Returns:
      the argument value

    • addPCRestore

      public int addPCRestore​(int value)
      Add a new "back step" (the undo action) to the stack. The action here is to restore the program counter.
      Parameters:
      value - The "restore" value to be stored there.
      Returns:
      the argument value

    • addCoprocessor0Restore

      public int addCoprocessor0Restore​(int register, int value)
      Add a new "back step" (the undo action) to the stack. The action here is to restore a coprocessor 0 register value.
      Parameters:
      register - The affected register number.
      value - The "restore" value to be stored there.
      Returns:
      the argument value

    • addCoprocessor1Restore

      public int addCoprocessor1Restore​(int register, int value)
      Add a new "back step" (the undo action) to the stack. The action here is to restore a coprocessor 1 register value.
      Parameters:
      register - The affected register number.
      value - The "restore" value to be stored there.
      Returns:
      the argument value

    • addConditionFlagSet

      public int addConditionFlagSet​(int flag)
      Add a new "back step" (the undo action) to the stack. The action here is to set the given coprocessor 1 condition flag (to 1).
      Parameters:
      flag - The condition flag number.
      Returns:
      the argument value

    • addConditionFlagClear

      public int addConditionFlagClear​(int flag)
      Add a new "back step" (the undo action) to the stack. The action here is to clear the given coprocessor 1 condition flag (to 0).
      Parameters:
      flag - The condition flag number.
      Returns:
      the argument value

    • addDoNothing

      public int addDoNothing​(int pc)
      Add a new "back step" (the undo action) to the stack. The action here is to do nothing! This is just a place holder so when user is backstepping through the program no instructions will be skipped. Cosmetic. If the top of the stack has the same PC counter, the do-nothing action will not be added.
      Returns:
      0