Homework 4
Due Monday, February 26


1.  Add a VADD instruction (non-pipelined) to Mac-1.  It will have
    op code 11111111wwwwwwww, and will perform the operation

       X <-- X + Y

    where X and Y are integer vectors of length N.  Beginning at
    word sp+wwwwwwww in memory, three consecutive words will contain
    the addresses of X and Y, and the value of N, respectively.

    Write a Mac-1 program to test VADD, and determine the number
    of cycles saved by using VADD instead of a loop of Mac-1
    instructions.  (One cycle corresponds to one microinstruction.)

2.  Consider a feedback pipe consisting of four stages, in which
    a task goes through the sequence S1, S2, S3, S4, S1, S2 (i.e.
    taking 6 time slots per task).  This corresponds to the
    reservation table

        1  2  3  4  5  6
    S1  x           x
    S2     x           x
    S3        x
    S4           x

    Determine the finite-state machine, and all loops of minimal 
    average latency.

    The following information will help you partially verify 
    that your answer is correct.  There are 8 states, and the 
    MAL value is 2.  The state (0,0,1,1) has an arc labeled "2"
    leading to the state (1,1,0,1), which in turn has an arc
    labeled "3" to the state (1,0,0,1).