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CSE 379
Lab #4

Objective
In this part of the lab, you will learn to use general purpose I/O to interface hardware with the ARM
processor and begin to create a library for your subroutines. You will utilize four LEDs, four momentary
push buttons, the RGB LED, and the keypad on the EduBase Board.
Description
Write and test four ARM assembly language subroutines, called read_from_push_btns, illuminateLEDs,
illuminate_RGB_LED, and read_from_keypad. Once written, write a subroutine, called lab4, which has a
menu that allows you to repeatedly do the following until the user decides to exit the program. Note that
instructions on how to use the program (such as what the menu choices are and what user input is
expected) is required.
• Display a binary value between 0000 and 1111 on the LEDs. LED3 is the MSB while the LED0
is the LSB. A 1 should turn on the LED and a 0 should turn it off.
• Read a value from the momentary push buttons. The binary value read should be displayed in
hexadecimal in PuTTy.
• Display, in PuTTy, the key that is pressed on the keypad Only keys 0 through 9 will be tested.
• Illuminate or turn off the RGB LED. When illuminating the RGB LED, the user should be
allowed to select the color (red, green, blue, purple, yellow, or white) via PuTTy.
The Library
Incorporate the following subroutines into a separate library file called library_lab_4.s.
• uart_init initializes the user UART for use.
• output_character transmits a character passed into the routine in r0 to PuTTy via the UART.
• read_character reads a character from PuTTy via the UART, and returns the character in r0.
• read_string reads a string entered in PuTTy and stores it as a null-terminated string in memory.
The user terminates the string by hitting Enter. The base address of the string should be passed
into the routine in r4. The carriage return should NOT be stored in the string.
• output_string displays a null-terminated string in PuTTy. The base address of the string should be
passed into the routine in r4.
• read_from_push_btns reads the momentary push buttons, and returns the value read in r0. Push
button 2 should correspond to the MSB and 5 to the LSB.
• Illuminate_LEDs illuminates the four LEDs. The pattern indicating which LEDs to illuminate is
passed into the routine in r0. Bit 3 corresponds to LED 3, bit 2 to LED 2, bit 1 to LED 1, and bit
0 to LED0.
• illuminate_RGB_LED illuminates the RBG LED. The color to be displayed is passed into the
routine in r0. How the individual colors are encoded when passed into the routine in r0 is up to
you. You should provide for the RGB LED to be illuminated red, blue, green, purple, yellow.,
and white.
• read_from_keypad reads a keypress on the keypad, and returns the value corresponding to the key
that was pressed in r0. Only keys 0 through 9 will be tested.
Skeleton Code
The following skeleton code shown below can be used to get you started with your library file.
.text
.global uart_init
.global output_character
.global read_character
.global read_string
.global output_string
.global read_from_push_btns
.global illuminate_LEDs
.global illuminate_RGB_LED
.global read_keypad
uart_init:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
output_character:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
read_character:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
read_string:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
output_string:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
read_from_push_btns:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
illuminate_LEDs:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
illuminate_RGB_LED:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
read_keypad:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
.end
To access these routines from lab_4.s, be sure to declare the labels as global, as shown below.
.text
.global uart_init
.global output_character
.global read_character
.global read_string
.global output_string
.global read_from_push_btns
.global illuminate_LEDs
.global illuminate_RGB_LED
.global read_keypad
.global lab4
lab4:
STMFD SP!,{lr} ; Store register lr on stack

; Your code is placed here

LDMFD sp!, {lr}
MOV pc, lr
.end
Partners
You will work with a partner in this lab. Your partner MUST be the same partner you worked with on lab
#3.
Documentation
Your program must be clearly commented, and documentation must also be provided. The
documentation must follow the guidelines covered in lecture (found on the Lectures webpage of the
course website). Your comments should describe what each section of your program does. To receive
full credit on your documentation, you must submit a draft of your flowchart before you start working on
the lab in your regularly scheduled lab time on Monday, February 24 or Tuesday, February 25.
Submissions
Your source code (C and assembly) must be submitted online using the submit command (submit_cse379
Your source code (C and assembly) and your documentation (as a PDF) must be submitted online using
the submit command (submit_cse379 lab_4_wrapper.c lab_4.s lab_4_library.s lab_4_documentation.pdf)
on timberlake.cse.buffalo.edu before 11:59 PM on Tuesday, March 3, 2020. A hardcopy of your
documentation is due at the beginning of class on Wednesday, March 4, 2020. Your documentation will
be used along with the code you submitted when you perform the debug exercise for Lab #4.