- [30] How many clock periods does the following SPIM code segment take given a) no pipeline,
b) a 5 stage pipeline assuming one clock period per instruction, but no data forwarding,
c) a 5 stage pipeline with data forwarding as described in P&H, Chapter 6,
section 4.
or $t1,$0,$a2
or $t3,$0,$a0
or $t4,$0,$a1
lw $t5,0($t7)
lw $t6,0($t8)
mul $t2,$t5,$t6
addi $t1,-1
add $t3,$a3,$t3
add $t4,$a3,$t4
- [20] Find the data hazards in the following SPIM code segment, and show the
hazards on a pipeline diagram, as in P&H, Fig. 6.44:
lw $t1,i1
addi $t1,$t1,100
or $t2,$t3,$t1
add $a0,$a1,$t2
ori $a0,$a0,42
add $t5,$a0,$t2
- [10] Reorder the following code segment to remove the data hazards. Assume that
data forwarding takes place:
lw $t0,24($a0)
sub $t4,$t4,$t0
sub $t8,$t8,$t3
add $t6,$t6,$t5
mul $t7,$t7,$t1
- [10] What is the CPI for the reordered sequence of instructions in the preceding
problem?
- [20] Find the control hazards in the following SPIM code segment, and show the
hazards on a pipeline diagram::
la $t0, ar2
lw $t1, size
lw $t2, nrows
lw $t3, ncols
addi $t4, $t2, -1 # nrmax
addi $t5, $t3, -1 # ncmax
ori $t6, $0, 0 # initialize row index to 0
lwc1 $f0, val
mfc1 $s4, $0
rloop: mul $t9, $t6, $t3 # multiply rindex by ncols
mul $t9, $t9, $t1 # multiply by size of one array element to get roffset
ori $t7, $0, 0 # initialize column index to 0
cloop: mul $s0, $t7, $t1 # multiply cindex by size to get coffset
add $s1, $s0, $t9 # offset of ar2[rindex][cindex] = roffset + coffset
add $t8, $s1, $t0 # address of ar2[rindex][cindex] = offset + base
sw $s4, 0($t8) # store val in ar2[rindex][cindex]
addi $t7, $t7, 1 # increment the column index
sub $s2, $t5, $t7 # nc = ncmax - cindex
bgez $s2, cloop # branch back to cloop if nc >= 0
addi $t6, $t6, 1 # increment the row index
sub $s3, $t4, $t6 # nr = nrmax - rindex
bgez $s3, rloop # branch back to rloop if nr >= 0
ori $v0, $0, 10 # reach here if row loop is done
syscall # end of program!
- [10] Which instruction could do useful work in the branch delay slot,
without changing the computational results in any way?
or $t0,$0,$a0 # Reg. t0 points to the array element
or $t1,$0,$a2 # Reg. t1 is a counter
loop: sw $a3,0($t0) # Store the value into the array element
add $t0,$a1,$t0 # Increment the pointer by the value of size
addi $t1,-1 # Decrement the counter
bgtz $t1, loop # branch back to loop if counter >= 0
# (since we store at the head of the
# loop, we compute one more address
# than necessary just to reduce
# the number of compares & branches)
beamup: jr $ra # Beam me up....
Reading:
Review Exercises (DO NOT hand in):
