CS/ECE 252 Introduction to Computer Engineering

Primary contact for this homework: Rebecca Lam [rjlam@cs.wisc.edu]

You must do this homework in groups of two. Please write the full name and the student id of each member on every pages and staple multiple pages together. Only turn in ONE copy of homework per group.

Important Notes:

Problem 5 requires you to submit your code to the Learn@UW dropbox.

Submission guidelines:

1. For your your code submit only one archive file (*.zip or *.tar.gz) per group to the folder homework8.
2. Name the file with the following convention: lastname1lastname2.zip or lastname1lastname2.tar.gz
3. Your archive file should contain the following (The files MUST be named exactly like this):
   1. hw8_p5.asm - Assembly code for problem 5
   2. README.txt - Readme file that contains the names and student IDs for all members of your group
4. You can submit your code for problem 5 as many times as you want until 11:00 AM on Friday Dec. 9. After that time we will consider your latest submissions for grading.

Problem 1 (2 points)

After reading the article RFID Inside, answer the following questions with 1 sentence each:

1. What are the benefits of RFID tags?
   They hold information on identity, physiological characteristics, health, nationality, security clearances for purposes of healthcare, services, etc.
2. What are potential problems / issues with RFID tags?
   There are concerns regarding privacy, confidentiality, ethics of universal tagging, and body integrity.

Problem 2 (8 points)

Suppose we want to write a program in LC-3 that will be able to take a 16-bit value stored in memory and find the ASCII characters for its hex representation. For instance, we have a value stored at num = 0x12AB. The result should be stored in the memory pointed to by res such as follows: valueAt[res] = 'B' = 0x0042, valueAt[res+1] = 'A' = 0x0041, valueAt[res+2] = '2' = 0x0032, valueAt[res+3] = '1' = 0x0031.

The following program does this task by converting each 4-bit chunk of the 16-bit value into ASCII and storing it into the result array. It has one subroutine rshift, which right shifts the value in R1 by 4 bits and stores it into low4. Fill in the missing parts of the code indicated by ____.

 
; 
; Translate a 16-bit number into hex, ASCII style
;
	.ORIG	x3000
	ld	R3, four	; R3 is the counter
	ld	R1, num
	lea	R4, res		; R4 = pointer to result
loop	and	R0, R1, x0F	; Mask the lowest 4 bits
	add	R2, R0, #-10	; Check if > 9
	brzp	alpha
	ld	R5, numeric	; gets it to the 0-9 range
	brnzp	next
alpha	ld	R5, alphabt	; gets it to the A-F range
next	add	R0, R0, R5
	str	R0, R4, #0
	add	R4, R4, #1	; increment pointer
	add	R3, R3, #-1	; decrement counter
	brnz	end		; stop the loop
	jsr	rshift		; Right shift R1
	ld	R1, low4
	brnzp	loop
end	halt

rshift	ld	R0, twelve	; left shifts R1 by 12 and stores result in low4
	and	R2, R2, #0
rloop	add	R2, R2, R2	; Shift left R2
	add	R1, R1, #0
	brzp	skip
	add	R2, R2, #1
skip	add	R1, R1, R1	;Shift left
	add	R0, R0, #-1	
	brp	rloop
	st	R2, low4
	ret	

four	.FILL	#4
twelve	.FILL	#12
numeric	.FILL	#48	; offset used to get to numeric ASCII range
alphabt	.FILL	#55	; offset used to get to alphabetic ASCII range
low4	.BLKW	1
num	.BLKW	1
res	.BLKW	4	; where mem[Res] = lowest char to highest

Problem 3 (4 points)

The following program outputs ABCFGH out to the monitor. Fill in the missing parts of code.

 
	.ORIG x3000
	LEA	R1, TESTOUT
BACK_1	LDR	R0, R1, #0
	BRz	NEXT_1
	TRAP	x21
	ADD	R1, R1, #1
	BRnzp	BACK_1
		
NEXT_1	LEA	R1, TESTOUT
BACK_2	LDR	R0, R1, #0
	BRz	NEXT_2
	JSR	SUB_1
	ADD	R1, R1, #1
	BRnzp	BACK_2
NEXT_2	HALT
SUB_1	ADD	R0, R0, #5
K	LDI	R2, DSR
	BRzp	K	
	STI	R0, DDR
	RET
DSR	.FILL xFE04
DDR	.FILL xFE06
TESTOUT	.STRINGZ "ABC"
	.END

Problem 4 (6 points)

What does the following program do, in 4 or less sentences?

 
		.ORIG x3000
		LEA	R1, HELLO
AGAIN		LDR	R2, R1, #0
		BRz	NEXT
		ADD	R1, R1, #1
		BR	AGAIN
NEXT		LEA	R0, PROMPT
		TRAP	x22
		LD	R3, NEGENTER
AGAIN2		TRAP	x20
		TRAP	x21
		ADD	R2, R0, R3
		BRz	CONT
		STR	R0, R1, #0
		ADD	R1, R1, #1
		BR	AGAIN2
CONT		AND	R2, R2, #0
		STR	R2, R1, #0
		LEA	R0, HELLO
		TRAP	x22
		TRAP	x25
NEGENTER	.FILL	xFFF6		; -x0A
PROMPT		.STRINGZ "Please enter your name: "
HELLO		.STRINGZ "HELLO, "
		.BLKW #25
		.END

Problem 5 (10 points)

Now let's modify the program we wrote in homework 7 problem 5, the countdown timer. You may use your own code from before, or use the provided solution assembly file (Problem 5 Solution). Change the program in the following ways:

1. (8 points) Change the timer to handle inputs of two digit hex values (e.g. 1B->1A->19). When representing values less than 0x10, it will display it as 0#. For instance, 9 will be represented as 09.
2. (2 points) In addition to the above, modify your code so that the color of the timer output changes to green when the number is less than or equal to 05. For example, if we start our counter with 29, it should be RED when displaying 29 to 06 and GREEN when displaying 05 to 00.

Implement this task with minimal changes to the existing subroutines (it can be done without modifying any subroutines except DISPLAY).

Solution file: (hw8_p5.asm)

Color encoding: Each location holds a 16-bit value which determines the color of that pixel. The high-order bit is ignored, and the remaining 15 bits specify the color, using a 5-bit values for each of red [14:10], green [9:5], and blue [4:0]. The codes of the colors you would need for your program (BLACK and RED) is given to you in the code provided, however if you are curious to know the value for some other common colors, here are a few of them: