CS 224, F2015
Homework #5
S05: Stacks / Interrupts
Name
Questions:
Answers:
Section
Score
/ 38
1. (3 points) Define subroutine cohesion. What
properties of cohesion should be found in your
subroutines?
2. (3 points) Define subroutine coupling. What
properties of coupling should be found in your
subroutines?
3. (6 points) What is wrong (if anything) with the
following blinky program?
DELAY
mainloop:
xor.b
push.w
call
jmp
delay:
push.w
mov.w
delay02:
dec.w
jne
dec.w
jne
pop.w
ret
.equ
100
#0x01,&P1OUT ; toggle P1.0
#DELAY
; pass delay
#delay
; call delay
mainloop
r15
#0,r15
; callee-save
; init counter
r15
delay02
2(SP)
delay02
r15
;
;
;
;
;
;
delay over?
n
y, outer done?
n
y, restore r15
return
4. (6 points) What would be the difference in code size
and the cycles used to toggle the LED on and off then
(assume it is off), if the delay subroutine below was
placed in-line?
DELAY
mainloop:
xor.b
mov.w
call
jmp
delay:
dec.w
jne
ret
.equ
10
#0x01,&P1OUT ; toggle P1.0
#DELAY,r15
; pass delay
#delay
; call delay
mainloop
r15
delay
BYU, CS 224, F2015
; delay over?
; n
; y, return
Homework #5
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5. (4 points) What values may be found in a
subroutine activation record?
6. (6 points) When an Internet surfer opens Google
and types in a keyword, the command goes to one of
the company’s U.S. data centers, which are large-scale
facilities with hundreds of computer servers. In the
last seven years (2002-2008), the utility bills to power
and cool the servers and auxiliary equipment at U.S.
data centers increased from $15 billion to $30 billion
in 2008. List 3 ways we as computer software
developers, can reduce power consumption and realize
significant environmental and economic benefits?
7. (4 points) Power consumption is directly related to
the number of instruction cycles used by a system.
Show and explain the difference in power
consumption between
a. adding a Program A (that uses a billion cycles on
startup and then another billion cycles once per
subsequent year) to a system, and
b. adding a single extra instruction cycle to an
existing Program B (which executes 1024 times per
second).
Explain your answer in terms of cycles per year.
8. (6 points) A watch crystal has a strange looking
frequency of 32,768 Hz (cycles/second). This
frequency is convenient for real-time clocks because it
is the largest positive value that can be used with a
decrementing 16-bit counter. When the timer counts
down to zero, one second has expired.
a. John Harrison’s H4 chronometer (clock)
accumulated an error of 5.1 seconds over 81 days
when it was first taken to sea for testing in 1761. A
typical watch crystal has an error of 20 parts per
million (ppm). How many times more accurate was
Harrison’s clock than a watch crystal controlled
clock?
b. How accurate of a crystal is needed for a real-time
clock (in parts per million error) in order to be at least
as accurate as Harrison’s clock?
(Hint: Read “Clock accuracy in ppm” found in the
Readings section of References.)
BYU, CS 224, F2015
Homework #5
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