Question $1(20$ points$)$

The following program implements a stack that grows down toward high memory addresses as items are pushed, and the stack pointer points to the top item on the stack.

$```$

ENTRY

LDR SP$,=$STACK

MOV r$0,$ #$0$x$11$

MOV r$1,$ #$0$x$22$

PUSH$\_$R$0$ instruction$\_1$

PUSH$\_$R$1$ instruction$\_2$

POP$\_$R$0$ instruction$\_3$

POP$\_$R$1$ instruction$\_4$

Loop B Loop

space $32$

STACK DCD $0$x$0$

space $32$

END

$```$

AREA prog, CODE, READWRITE

Using ONLY LDR$/$STR instructions:

$-$ Write one instruction $($instruction$\_1)$ to push the value of RO onto the stack.

$-$ Write one instruction $($instruction$\_2)$ to push the value of R$1$ onto the stack.

$-$ Write one instruction $($instruction$\_3)$ to pop from the stack a value and to save it in RO$.$

$-$ Write one instruction $($instruction$\_4)$ to pop from the stack a value and to save it in R$1.$ Make sure that the values of R$0$ and R$1$ are swapped after these operations.

What are the $4$ instructions you used?

Write your answer $($i$.$e$.,$ the $4$ instructions$)$ in TWO parts, the mnemonic in a box and ALL operands in another box.

To facilitate automatic marking,

$-$ Use CAPITAL letters ONLY$--$except $0$x$,$ make it a small letter.

$-$ Do NOT leave ANY spaces between operands.

The mnemonic of the $1$st instruction is:

The operands of the $1$st instruction are:

The mnemonic of the $2$nd instruction is:

The operands of the $2$nd instruction are: $.$

The mnemonic of the $3$rd instruction is:

The operands of the $3$rd instruction are:

The mnemonic of the $4$th instruction is:

The operands of the $4$th instruction are: How many elements can be pushed onto this stack?

Encode the $1$st instruction to ARM machine language code. Write your answer as eight hexadecimal digits, each digit in a box. $0$x

A A A A A A A A A A A A A A