MIPS Assembly input from keyboard fail

Question

I am trying to write a MIPS code that open a file, reads it and prints out a single line when user inputs enter (new line) from keyboard, until the end of text document. But somehow program skips user inputs and do not wait for input.

Code:

.data
buffer: .space 4
fin: .asciiz "input.txt" # filename for input
myName: .asciiz "\nTheUserName"

.text
openfile:
li   $v0, 13       # system call for open file
la   $a0, fin      # board file name
li   $a1, 0        # Flag for reading
li   $a2, 0
syscall
add $s7, $v0, $0 # save the file descriptor
read:
#read from file code goes here
li   $v0, 14       # system call for read from file
move $a0, $s7      # file descriptor 
la   $a1, buffer   # address of buffer to which to read
li   $a2, 1        # hardcoded buffer length
syscall
beq $v0,$0,exit #exit if EOF is seen
print:
#print file code goes here
la $a0, buffer       # address of string to be printed
li $v0, 4            # print string
syscall
beq $a0,0x0A, input #check whether the character read from the file is ‘\n’ (new line) or not
b read
input:
#get input code goes here
li $v0, 12
syscall
beq $v0, 0x0A, read #check whether the character read from the keyboard is ‘\n’ (new line) or not
b input
exit:
# Close the file code goes here
li   $v0, 16       # system call for close file
move $a0, $s7      # file descriptor to close
syscall # close file
name:
# Print your name and surname on the screen as a string as the last line
li $v0, 4
la $a0, myName
syscall

Input file:

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris tristique dui at ornare pretium.
Phasellus ac vehicula libero. Fusce scelerisque dolor ipsum, vitae suscipit sapien dictum quis.
Praesent sed libero tellus. In vitae laoreet massa.
Duis vehicula fringilla orci, et iaculis nulla malesuada in.
Nam at cursus nisi. Duis convallis magna quis dolor aliquam ullamcorper.
Nunc sollicitudin a leo in placerat. Cras id pretium ligula, sed facilisis massa.
Curabitur semper ultricies nulla non lacinia. Nunc a fermentum ex, nec egestas ligula.
Quisque varius libero sed rhoncus venenatis. Cras pulvinar ultrices dignissim.

Craig Estey Craig Estey · Accepted Answer · 2016-10-08T19:37:23

Okay, I fixed your program.

The main problem was the the test for newline from file input was incorrect. You were comparing $a0 [which was the buffer address] against newline and not the first character of the buffer.

There were two other bugs as well.

I've annotated the bugs along with the fixes [please pardon the gratuitous style cleanup]:

    .data
buffer:     .space      4
fin:        .asciiz     "input.txt"     # filename for input
myName:     .asciiz     "\nTheUserName"

    .text

openfile:
    li      $v0,13                  # system call for open file
    la      $a0,fin                 # board file name
    li      $a1,0                   # Flag for reading
    li      $a2,0
    syscall
    add     $s7,$v0,$0              # save the file descriptor
# NOTE/BUG: this line was missing -- actually it may be optional -- try with
# and without it to see the effect:
    b       input                   # pause for user input _before_ 1st line

read:
    # read from file code goes here
    li      $v0,14                  # system call for read from file
    move    $a0,$s7                 # file descriptor
    la      $a1,buffer              # address of buffer to which to read
    li      $a2,1                   # hardcoded buffer length
    syscall
    beq     $v0,$0,exit             # exit if EOF is seen

print:
    # print file code goes here
    la      $a0,buffer              # address of string to be printed
# NOTE/BUG: add the following line:
    sb      $zero,1($a0)            # ensure we have EOS at end of string
    li      $v0,4                   # print string
    syscall
# NOTE/BUG: add the following line -- it was the _real_ bug:
    lb      $a0,0($a0)              # get buffer char value
    beq     $a0,0x0A,input          # is file char newline?
    b       read

input:
    # get input code goes here
    li      $v0,12
    syscall
    beq     $v0,0x0A,read           # is keyboard char newline?
    b       input

exit:
    # Close the file code goes here
    li      $v0,16                  # system call for close file
    move    $a0,$s7                 # file descriptor to close
    syscall                         # close file

name:
    # Print your name and surname on the screen as a string as the last line
    li      $v0,4
    la      $a0,myName
    syscall

    li      $v0,10
    syscall

MIPS Assembly input from keyboard fail

1 Answers