231 Fall 2007 -- Exam 1                     Name:________________________

Word Bank - questions 1-8.  Place the appropriate term by its description
below.  (2 pts. each)

  accumulator machine        direct addressing          immediate value
  load/store machine         indexed addressing         memory location
  stack machine              indirect addressing        register

  ALU      load      address      instruction      location counter (loc)
  CPU      store     label        pseudo-op        program counter (PC)


1. _____________________ an assembly language statement that doesn't
                         generate a machine instruction but instead acts
                         as a directive to the assembler

2. _____________________ an instruction that will make a copy of the
                         value in the accumulator (or other register)
                         and place it into a specified memory word

3. _____________________ unit within a computer that performs arithmetic
                         and logical computations (it has no registers)

4. _____________________ machine design in which an add instruction only
                         has an opcode (the source operands are fetched
                         from, and the result is stored in, a structure
                         within the CPU)

5. _____________________ a symbolic name in an assembly language program
                         used to access data or as a branch target

6. _____________________ addressing mode in which the instruction holds
                         the address of a memory word which contains the
                         address of the memory word which is accessed as
                         data

7. _____________________ register in the CPU that contains the address of
                         the memory word from which the next instruction
                         will be fetched

8. _____________________ a number used as the name of a memory location


9. Define "assembly language" and "machine language", clearly indicating
   both the difference between them and the relationship between them.
   (8 pts.)


Give the power of ten that corresponds to these prefixes.  (2 pts. each)

10. mega     _____________        12. milli    _____________

11. giga     _____________        13. micro    _____________


14. (a) Why do assemblers use two passes?  ______________________________
        (Hint: two words.)  (2 pts.)

    (b) What does the first pass do?   increment the ____________________
        (Hint: two words each.)          and
        (2 pts. each)                  build the ________________________

    (c) What does the second pass do?  __________________________________
        (Hint: one word.)  (2 pts.)


15. On the right hand side, give the symbol table produced by the first
    pass of the assembler for the following accumulator machine program.
    (12 pts.)

        word(data,five)
        word(five,5)
        word(ten,10)
      label(start)
        load(ten)
        sub(ten)
        store(data)
        halt
      end(start)


16. The opcodes for the load, sub, store, and halt instructions are 50,
    30, 60, and 0, respectively.  On the right hand side give the
    executable file produced by the second pass of the assembler for the
    following accumulator machine program.  (14 pts.)

        word(data,five)

        word(five,5)

        word(ten,10)

      label(start)

        load(ten)

        sub(ten)

        store(data)

        halt

      end(start)


accumulator machine instruction set

opcode address operation name                   machine action
------ ------- --------------                   --------------
 halt   ----   halt                             stop execution
 div    addr   divide                           acc = acc/memory[addr]
 mul    addr   multiply                         acc = acc*memory[addr]
 sub    addr   subtract                         acc = acc-memory[addr]
 add    addr   add                              acc = acc+memory[addr]
 load   addr   load                             acc = memory[addr]
 store  addr   store                            memory[addr] = acc
 ba     addr   branch always                    pc = addr
 blt0   addr   branch on less than              if acc<0  then pc = addr
 ble0   addr   branch on less than or equal     if acc<=0 then pc = addr
 beq0   addr   branch on equal                  if acc==0 then pc = addr
 bne0   addr   branch on not equal              if acc/=0 then pc = addr
 bge0   addr   branch on greater than or equal  if acc>=0 then pc = addr
 bgt0   addr   branch on greater than           if acc>0  then pc = addr

17. Analyze this program segment and provide a concise explanation of
    what it does.  Be accurate but also be as brief as possible in
    conveying the effect of the segment.  (E.g., a line-by-line
    narrative is nonresponsive.)  (8 pts.)

        word(a,__)
        word(b,__)
        word(c,__)
          ...
        load(a)
        sub(b)
        blt0(there)
        load(a)
        store(c)
        ba(done)
      label(there)
        load(b)
        store(c)
      label(done)


18. Give the output and explain what the following m4 macro does when
    called as "test(0)"  (8 pts.)

      define(`test',`ifelse(len($1),0,equal,not equal)')


Extra Credit 1.  Give the output and explain what the redefined m4 macro
does when called as "test(3)".  (Note the absence of quotes in the body
of the definition.) (4 pts.)

      define(`test',ifelse(len($1),0,equal,not equal))


19. Write code that implements the expression y = ((x-1)*(x-7))/(x-11)
    in the assembly language for the accumulator machine.  Do not
    overwrite source operands.  (18 pts.)

    Assume this data section:
      word(one_m,1)
      word(seven_m,7)
      word(eleven_m,11)
      word(x_m,1)
      word(y_m,0)
      word(temp1_m,0)
      word(temp2_m,0)
    comment(`add others if needed')


Extra credit 2.  (up to 6 pts.)

We discussed in class how an algorithm could be fully implemented
in hardware, fully in software, or in a hybrid manner.  Consider
implementing an assembler fully in hardware.  Identify and explain
the pros and cons of doing so.  (Knee-jerk responses will garner
some credit, but well-thought-out and well-expressed responses
will receive more credit.)