Stacks

Question 1

How can stacks be imaged

Answer 1

As a stack of paper
You can on,y out new things on the top
You cannot put new things in the middle
You can only take things off the top
You can see the top without taking off the top

Question 2

What does it mean to push an item on a stack

Answer 2

To place an item on the top of the stack

Question 3

What does it mean to push an item off the stack

Answer 3

To remove an item from the top of the stack

Question 4

What does SP stand for

Answer 4

Stack pointer

Question 5

In what register is the system stack SP

Answer 5

R13

Question 6

What are the four types of stack growth conventions

Answer 6

Full ascending
Full descending
Empty ascending
Empty descending

Question 7

In a full ascending stack:

1. Where does the SP point
2. What direction does it grow in memory

Answer 7

1. SP points at last item pushed onto the stack

2. Grows from low to high address in memory

Question 8

In a full descending stack:

1. Where does the SP point
2. What direction does it grow in memory

Answer 8

1. SP points to last item pushed onto stack

2. Grows from high to low address in memory

Question 9

In a empty ascending stack:

1. Where does the SP point
2. What direction does it grow in memory

Answer 9

1. Sp posts to the next free space in the stack

2. Grows from low to high addresses in memory

Question 10

In a empty descending stack:

1. Where does the SP point
2. What direction does it grow in memory

Answer 10

1. Sp points to next free space on the stack

2. Grows from low to high addresses in memory

Question 11

What is it called when we reach stack size limit

Answer 11

Stack overflow

Question 12

Does popping off get done on its own

Answer 12

No it’s the programmers responsibility

Question 13

What does LDM do

Answer 13

Load multiple

Question 14

What does STM so

Answer 14

Store multiple

Question 15

Eg store contents of registers r1, r2, r3 to memory at the address in r12

Answer 15

STMDB R12, {r1-r3}

DB = decrement before

Question 16

Load r1, r2, r3 with contents of memory at the address in r12

Answer 16

LDMIA R12, {R1 - R3}

Question 17

What do the two letters after LDRM and STRM mean

Answer 17

Mode of operation
Ie IA = increment after
DB = decrement before

Question 18

Does LDM/STM support byte sized memory transfers

Answer 18

No only word sized

Question 19

Is the order that the registers are specified in the Curley brcakets important

Answer 19

No

Question 20

In what order will registers be pushed onto stack

Answer 20

The lowest register is always put at the lowest address and the highest register t the highest

Question 21

Why would you use ! With the sp

Answer 21

To make sure that it gets updated each time

Question 22

Eg push r3, updating sp

Answer 22

STMDB SP! {R3}

Question 23

Pop r3 and update SP

Answer 23

LDMIA SP! {r3}

Question 24

What mode of order is assumed if not specified otherwise

Answer 24

Full descending

Question 25

Instead of specifying increment after and decrement before, what could you use

Answer 25

FD for full descending eg
STMFD
LDMFD