Write a PLP Assembly program that receives a string of characters via the UART, checks if this string is a palindrome, and then uses a print function to print either Yes or No.

A palindrome sequence of characters (typically a word or phrase) that is the same both forwards and backwards. For this, strings will be terminated using a period (.). Assume a string will contain at least one character in addition to a period. You will not need to handle empty strings or strings with only a period. The program should be able to handle multiple strings sent one after another or concatenated together. For example, the string: abba. data. should print Yes followed by No on the next line. Spaces should be ignored when checking for a palindrome and the palindrome should not be case sensitive. For example, A nut for a jar of Tuna. would be considered a palindrome.

When called, depending on the value in register $a0, the following string will be displayed on the simulated UART devices output : call project3_print If $a0 contains a zero then No will be displayed and if $a0 contains a non-zero value (e.g. one) then Yes will be displayed.

To use the print function, the PLP program needs to initialize the stack pointer ($sp) before performing the function call (or any other operations involving the stack pointer). For this reason, the skeleton project file includes an initialization that sets the stack pointer to 0x10fffffc (the last address of RAM).

A skeleton PLP project code is available below. ________________________________________________________________

2 Source Files provided:

.org 0x10000000

# Initializations

li $sp, 0x10fffffc

# Initialize any registers you will be using here.

main:

# TODO: write your primary program within this loop

j main

nop

________________________________________________________________

li $a0, control_message_p3

jal libplp_uart_write_string_p3

nop

control_flow_trap_p3:

j control_flow_trap_p3

nop

bcd_storage_p3:

.space 10 #creates 10 words here

invalid_char_p3:

.asciiz "Error: Invalid character "

control_message_p3:

.asciiz "Error: Program entered project3_print.asm due to missing control flow at the end of main.asm "

project3_print:

push $ra

beq $a1, $0, UART_no_error_p3 # Check for error

nop

li $a0, invalid_char_p3

jal libplp_uart_write_string_p3

nop

pop $ra

return

UART_no_error_p3:

#INITIALIZATIONS

# Saved Values

lui $s0, 0xF000 #UART

li $s1, 0x1 #mask for bit 0, used by put_char

li $s2, 0x2 #mask for bit 1, used by get_char

li $s3, 10 #used by decimal_to_binary

li $s4, 48 #subtract from ascii for decimal, used by decimal_to_binary

# Temporary Values

li $t0, 0 #counter in subroutines

li $t1, 0 #x: used for UART character reads and writes

# check if 0

bne $a0, $0, non-zero_input_p3

nop

addiu $t1, $0, '0' # set UART output value to '0'

jal put_char_p3

nop

addiu $t1, $0, 10 # set UART output value to ' '

jal put_char_p3

nop

pop $ra

return

non-zero_input_p3:

# Get sign bit

move $t2, $a0

srl $t2, $t2, 31

beq $t2, $0, non_negative_output_p3

nop

jal handle_negative_p3

nop

non_negative_output_p3:

jal to_bcd_p3

nop

jal display_bcd_p3

nop

pop $ra

return

#=======================================FUNCTIONS=======================================

#Description: places number result ($s7) into the space at the label bcd_storage

#Resources: #uses $t0, t2, $t3, $t4

to_bcd_p3:

push $ra

li $s5, bcd_storage_p3

#set 10's place followed call subtract function to store bcd

li $s6, 1000000000 #10

jal base10_subtract

nop

li $s6, 100000000 #9

jal base10_subtract

nop

li $s6, 10000000 #8

jal base10_subtract

nop

li $s6, 1000000 #7

jal base10_subtract

nop

li $s6, 100000 #6

jal base10_subtract

nop

li $s6, 10000 #5

jal base10_subtract

nop

li $s6, 1000 #4

jal base10_subtract

nop

li $s6, 100 #3

jal base10_subtract

nop

li $s6, 10 #2

jal base10_subtract

nop

li $s6, 1 #1

jal base10_subtract

nop

pop $ra

jr $ra

nop

#Description: repeats $s7 - $s6 as many times as possilbe, where s6 is a multiple of 10

#Resources: #uses $t0, t2, $t3, $t4

base10_subtract:

li $t5, 0 # bcd place value

sltu $t6, $a0, $s6 # determine if number less than decimal place

subtract_loop_p3:

bne $t6, $0, exit_sub_loop_p3

nop

subu $a0, $a0, $s6

addiu $t5, $t5, 1 #incriment bcd

sltu $t6, $a0, $s6 # determine if number less than decimal place

j subtract_loop_p3

nop

exit_sub_loop_p3:

sw $t5, 0($s5) # store bcd value

addiu $s5, $s5, 4 # increment BCD pointer to next word

jr $ra

nop

#Description: places number result ($s7) into the space at the label bcd_storage

#Resources: #uses $t0, t2, $t3, $t4

display_bcd_p3:

push $ra

li $t3, bcd_storage_p3

li $t2, 10 #count down for prints

# for 10 starting at bcd_storage, add 48 and put char

lw $t1, 0($t3)

remove_preceeding_zeros_p3:

bne $t1, $0, display_bcd_loop_p3 # branch if non-zero

nop

addiu $t3, $t3, 4 # increment BCD pointer

subu $t2, $t2, $s1 # decrement $t2

lw $t1, 0($t3)

j remove_preceeding_zeros_p3

nop

display_bcd_loop_p3:

# convert to ascii and print

addu $t1, $t1, $s4

jal put_char_p3

nop

addiu $t3, $t3, 4 # increment BCD pointer

subu $t2, $t2, $s1 # decrement $t2

lw $t1, 0($t3)

bne $t2, $0, display_bcd_loop_p3

nop

addiu $t1, $0, 10 # set UART output value to ' '

jal put_char_p3

nop

pop $ra

jr $ra

nop

#Description: outputs negative sign and converts from 2's compliment

# Resources: $s0 = UART, $s1 = 1, $a0 = number to convert, $t1 = character to print

handle_negative_p3:

push $ra # save return address

addiu $t1, $0, '-' # set UART output value to '-'

jal put_char_p3

nop

pop $ra # restore return address

# 2's compliment conversion

nor $a0, $a0, $a0

addu $a0, $a0, $s1

jr $ra

nop

#Description: Writes $t1 to UART

#Resources: $s0 = UART, $s1 = 1, $t0 = temp

put_char_p3:

lw $t0, 4($s0) # load status register

and $t0, $t0, $s1 # mask for clear to send

bne $t0, $s1, put_char_p3

nop

sw $t1, 12($s0) # store in send buffer

sw $s1, 0($s0) # command register: send

jr $ra

nop

# From PLP UART Library

libplp_uart_write_p3:

lui $t0, 0xf000 #uart base address

libplp_uart_write_loop_p3:

lw $t1, 4($t0) #get the uart status

andi $t1, $t1, 0x01 #mask for the cts bit

beq $t1, $zero, libplp_uart_write_loop_p3

nop

sw $a0, 12($t0) #write the data to the output buffer

sw $t1, 0($t0) #send the data!

jr $31

nop

libplp_uart_write_string_p3: #we have a pointer to the string in a0, just loop and increment until we see a \0

move $t9, $31 #save the return address

move $t8, $a0 #save the argument

libplp_uart_write_string_multi_word_p3:

lw $a0, 0($t8) #first 1-4 characters

ori $t0, $zero, 0x00ff #reverse the word to make it big endian

and $t1, $t0, $a0 #least significant byte

sll $t1, $t1, 24

srl $a0, $a0, 8

and $t2, $t0, $a0 #second byte

sll $t2, $t2, 16

srl $a0, $a0, 8

and $t3, $t0, $a0 #third byte

sll $t3, $t3, 8

srl $a0, $a0, 8 #last byte in a0

or $a0, $t1, $a0

or $a0, $t2, $a0

or $a0, $t3, $a0

beq $a0, $zero, libplp_uart_write_string_done_p3

nop

ori $t7, $zero, 4

libplp_uart_write_string_loop_p3:

jal libplp_uart_write_p3 #write this byte

addiu $t7, $t7, -1

srl $a0, $a0, 8

bne $a0, $zero, libplp_uart_write_string_loop_p3

nop

beq $t7, $zero, libplp_uart_write_string_multi_word_p3

addiu $t8, $t8, 4 #increment for the next word

libplp_uart_write_string_done_p3:

jr $t9 #go home

nop