In writing the project code, use only the following instructions and their variations for

conditional branching $($such as BEQ, BNE, etc$),$ conditional execution $($such as ADDEQ, etc$),$ size

designation $($such as LDRH$,$ etc$),$ and flagging $($such as SUBS etc$)$: ADD, AND, B$,$ BL$,$ BX$,$ CMP$,$

EOR, LDR$,$ LSL$,$ LSR$,$ MOV, ORR, PUSH, POP, ROR, RRX$,$ STR$,$ and SUB.

No other instructions are allowed. Use of not$-$allowed instructions results in $0$ point.

A$.$ Problem

For a DE$1-$SoC system, write an ARM assembly code which down counts from a decimal number

to $0$ by $1$ while displaying the numbers on the HEX$3-$HEX$07-$segments $($and$,$ optionally, at the

same time on the VGA screen to earn extra $20$ points. See Note $3$ below for details of this option$).$

The starting number is determined by the positions of SW$3-$SW$0,$ SW$3$ being the $1000$s position,

SW$2$ being $100$s position, SW$1$ for $10$s$,$ and SW$0$ for units. The following example clarifies a

decimal number obtained from SW positions:

Number SW$3$ SW$2$ SW$1$ SW$0$

$------------------$

$10001000$

$11011101$

$01000100$

Once the SW$3-$SW$0$ position determines the starting number, they are used no more. The counting

down process pauses when SW$8$ is pressed $($i$.$e$.,$ SW$8=1)$ and resumes when SW$8$ is released

$($SW$8=0).$ When testing your project code, after compilation, configure SW$3-$SW$0$ first, before

running the code.

Note $3$: On the screen with background colored by the pixel color determined by the last four$-$

digits of your Howard ID$,$ display the numbers horizontally at $(10,20)$ location of the monitor.

This option, if successfully implemented, earns extra $20$ points.

B$.$ Coding instruction