Assignment 2
Computer Organization and Software
COEN 311
Some of the solutions are here. The rest are similar.
Problem 1)
a) Write an assembly program, for a GPR machine having 8 general purpose registers
(R1,...,R7), to evaluate the following expression. Ignore the remainder part of the
division process.
( (a + b) / (a + d) ) * (a * e)
where a,b,d,e are variables with addresses A,B,D,E respectively, and each operation is
defined as follows:
+ --------> ADD Ri, Rj ( Rj <- Ri + Rj)
* --------> MULT Ri, Rj ( Rj <- Ri * Rj)
/ --------> DIV
Ri, Rj ( Rj <- Rj / Ri)
a = M[A] ------> content of memory location at address A.
same for B, D, E.
move A, D0
move B, D4
add D0, D4
move D, D1
add D0, D1
div D1,D4
move E, D2
mult D0, D2
mult D4, D2
; D0 = a
; D4 = b
; D4 = a + b
; D1 = d
; D1 = a + d
; D4 = (a + b) / (a + d)
; D2 = e
; D2 = (a * e)
; D2 = ( (a + b) / (a + d) ) * (a * e)
b) Evaluate the same expression on an Accumulator architecture. Conclude.
1/5
Problem 2)
a) Provide micro-instructions in the form of detailed flowchart for the execution of the
following instructions.
b) Show the flow of the micro-instructions within the GPR architecture by highlighting
the system buses and the registers used.
i)
ii)
iii)
iv)
move X, D0 ; move contents of memory location X to register D0
move D0, X ; move contents of register D0 to memory location X
movea 22(a3),25(a1) ; move contents from memory to memory
bgt.w label ; branch if greater than to location “label”
Answer 2)
For each of the above, for part b), draw the CPU consisting of all the registers (for
example MAR, MBR, PC, IR, Address and Data Registers, ALU) and Memory, and
show each of the micro-instruction as in part a).
i) move X, D0
Machine Instruction:
0011 0000 0011 1000
Address of X
a)
Micro-steps are:
MAR <-- PC
MBR <-- M[MAR]
IR <-- MBR
|
decode
|
PC <-- PC + 2
MAR <-- PC
MBR <-- M[MAR]
MAR  MBR
MBR  M[MAR]
D0  MBR
PC <-- PC + 2
; fetch
; PC points to source address
; address of X in MBR
; move X to MAR
; read contents of location X
;
; PC points to next instruction
ii) move D0, X
Machine Instruction:
0011 1110 0000 0000
Address of X
2/5
a)
Micro-steps are:
MAR <-- PC
MBR <-- M[MAR]
IR <-- MBR
|
decode
|
PC <-- PC + 2
MAR <-- PC
MBR  M[MAR]
MAR  MBR
MBR  D0
M[MAR]  MBR
PC <-- PC + 2
; fetch
; PC points to destination address
; read destination address X
; MAR has X now
; source data in MBR
; data in Effective address X (which is in MAR)
; PC points to next instruction
iii) movea 22(a3),25(a1)
Machine Instruction:
0011 0011 0110 1011
0000 0000 0001 0110
0000 0000 0001 1001
a)
Source Effective address = contents of a3 + $16
temp <--- M[a3 + $16]
Destination Effective address = contents of a1 + $19
M[a1 + $19] <- temp
Micro-steps are:
MAR <-- PC
MBR <-- M[MAR] ; fetch
IR <-- MBR
|
decode
|
PC <-- PC + 2
; PC points to source displacement
MAR <-- PC
MBR <-- M[MAR] ; source displacement loaded
MAR <-- [A3 + MBR]
; source effective address calculated
MBR <- M[MAR]
; source data in MBR
WR <- MBR
; saved temporarily since MBR is to be reused
PC <-- PC + 2
; PC points to destination displacement
MAR <-- PC
MBR <-- M[MAR] ; destination displacement loaded
3/5
MAR <-- [A1 + MBR]
; destination effective address calculated
MBR <- WR
; source data back to MBR
M[MAR] <-- MBR ; source data moved to destination
PC <-- PC + 2
; PC points to next instruction
iv) bgt.w label
Machine Instruction:
0110 1110 0000 0000
---- displacement ----
a)
MAR <-- PC
MBR <-- M[MAR]
IR <-- MBR
|
interpret
|
fetch
decode
TRUE
|
PC <-- PC + 2
MAR <-- PC
MBR <-- M[MAR] ; get displacement
PC <-- PC + MBR ; execute
FALSE
|
PC <- PC + 4
Problem 3)
Given the following assembly program P for GPR Processor:
1. Move X, R1
2. Move Y, R2
3. Add R1, R2
4. Move Z, R3
5. Mul R2, R3
6. Move X, R1
7. Add R1, R3
8. Move R3, L
a) What is this program doing?
b) Draw flowcharts showing the micro-step execution for each of the instructions 1,
3, 5 and 8.
c) Calculate the execution times of instructions 1, 3, 5 and 8 assuming:
Micro-step
Register Transfer
Number of clock cycles (cc)
1
4/5
Decoding
Add Execution
Multiply Execution
Memory Access
2
2
5
10
Instruction 1 micro-instructions are same as in Problem 2 i).
MAR <-- PC
; 1 cc
MBR <-- M[MAR] ; 10 cc
IR <-- MBR
; 1 cc
|
Decode
; 2 cc
|
PC <-- PC + 2
; 2 cc
MAR <-- PC
; 1 cc
MBR <-- M[MAR] ; 10 cc
D0  MBR
; 1 cc
PC <-- PC + 2
; 2 cc
_______
Total Clock cycles: 30 cc
d) Calculate the total execution time for the whole program P.
e) Rewrite program P using Accumulator architecture.
f) Calculate the total time needed for the new program P′ on the Accumulator
architecture.
g) Compare both P and P′, assuming they have the same clock speed.
5/5