CS270 Colorado State University

=========
PA3
=========








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LC3state

    Parts of the structure
        ControlState    cs;
            

        Word field for each of the registers.
            
            
        
        BIT enumerated type for N, Z, and P condition codes.
        
        memory array to hold simulated memory locations.
            
            

    Represents the full state of the LC3 machine.
        
        
        
        
        
            
            
            
            
    Passing around a pointer to LC3state instead of the whole structure.
        
        Recall the three possible things that can be stored in memory.
        
            
            
            
            
            
    
        Any variable in C declared with a star/asterix after the type is a
        pointer type and is meant to hold a memory address.
        
            

        Why passing around pointer to LC3state?
            
            
        Pointers to structures
            
            
    LC3state_equal
        Two LC3states are equal if all of their fields are equal.
            

            
                    
    alu
        ALU_ADD
        
        ALU_AND
        
        ALU_XOR
        
            
            
    decode
        
        
    
    LC3state_write_reg
        
    

    LC3state_read_mem
        [ m->MDR = m->memory

=========
LC3
=========

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Addressing Modes

    Addressing mode indicates where the operand is located.
        

    
    1. Register
    
        
    
        

    
    2. Immediate
    
        
    
        

    
    3. Memory
        The effective address is encoded in instruction 
        (direct or PC-relative).

            

                            
        
        Pointer to effective address is encoded in instruction
        (indirect)
        
            

            

        
        Pointer to the effective address is in a register.
        (relative, or base+offset)

            

            

            


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Datapaths

    
    
    

    


    ADD R2, R5, #-8
        
        
        
        
        
    
        
    
    
    ADD R1, R2, R3
        
        
        
        
        
    
    
        
    
    
    LDR R2, R3, x1D
    
            
        
        
        
        
        
    
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mstrout@cs.colostate.edu, 10/1/08