CSC $362$ Homework Assignment #$7$

Due Date: Wednesday, April $24$

Word Processor all answers, show work for partial credit.

$1)$ Architectures are considering one of two changes to their processor. The first is to increase

the L$1$ cache hit time from $\mathrm{.}5$ ns to $\mathrm{.}3$ ns per cycle. The processor operates while there are

no stalls in the pipeline. With this increase, they anticipate an average of $\mathrm{.}6$ stalls per

instruction. The second is to increase the TLB$$s size. Currently, the TLB has a miss rate of

$15\%$ but the increased size will change this to only $6\%.$ When the TLB misses, the page

table in DRAM must be accessed. DRAM access is $20$ ns $($recall from above, the L$1$ cache,

which includes the TLB$,$ can be accessed in $\mathrm{.}5$ ns$).$ Use Amdahl$$s Law to compute the

speedup of both options and state which should be implemented.

$2)$ Answer the following questions about the $4$ forms of I$/$O$.$

a$.$ Assume an input task requires moving $1024$ bytes from input to memory. Further,

assume that each transfer is $1$ byte at a time. Assume no errors occur.

i$.$ If this task was handled by programmed I$/$O$,$ how many interrupts would take

place?

ii$.$ If this task was handled by interrupt$-$driven I$/$O$,$ how many interrupts would

take place?

iii. If this task was handled by DMA I$/$O$,$ how many interrupts would take place?

iv$.$ If this task was handled by channel I$/$O$,$ how many interrupts would take place?

b$.$ What additional hardware will a DMA controller have over an I$/$O module that uses

interrupt$-$driven I$/$O$?$

$3)$ Use the figure on slide $11$ to answer the following questions.

a$.$ What are the D$1$D$0$ lines used for?

b$.$ In our computers, we do not use these two lines, what do we use in place of them

and why?

c$.$ Why should the keyboard have a higher priority over the disk drive to interrupt the

CPU?

$4)$ Assume we have six drives in a RAID configuration whereby a parity byte is stored using

five data bytes and stored on the sixth drive. We have the following values where the byte

on disk $4$ is inaccessible. What is this missing byte? $($restore it by using the other seven

bytes, assume even parity is used$)$

Disk $1$: $11101111$

Disk $2$: $10101110$

Disk $3$: $10101110$

Disk $4$: $------------$

Disk $5$: $00100100$

Parity: $01100010$

$5)$ Answer the following regarding RAID levels.

a$.$ How does RAID $5$ improve over RAID $4?$

b$.$ How does RAID $6$ improve over RAID $5?$

c$.$ RAID $0$ uses no redundancy so why would anyone select RAID $0$ at the added

expense of using RAID?

d$.$ Although RAID $3$ would provide a better performance over RAID $5,$ RAID $3$ is

seldom used, why?

$6)$ Answer the following questions regarding using a binary semaphore to implement

synchronization.

a$.$ Show how the wait and release functions are implemented.

b$.$ Why is the while loop in wait not an infinite loop?

c$.$ What would happen if we initialize the semaphore to $2$ instead of $1?$

d$.$ We implement wait and release using atomic instructions. What is an atomic

instruction and why should we use one to implement these functions?

$7)$ Given the C program below, provide the run$-$time stack as it would appear at point P$1.$ For

each variable$/$parameter on the stack, list it as well as its current value. You will have to

work through the logic of the code to determine the order that functions are called.

void main$()\{$

int x $=3$;

foo$($x$)$;

$\}$

void foo$($int a$)\{$

int b $=1$;

printf$(\%$d

$,$ bar$($a$)+$b$)$;

$\}$

int bar$($int z$)\{$

if$($z$>0)$ return bar$($z$-1)+1$;

else return dummy$()$;

$\}$

int dummy$()\{$

int c $=1$; $$ P$1$

return c;