学习MIPS汇编：读取文本并写入文件

Question

我正在尝试用MIPS汇编语言编写简单的程序。我要做的是从键盘读取多个字符并将其保存到文件。我正在使用13个操作码创建文件并使用15个操作码保存字符。我不明白：如何动态分配字符数来写入15个操作码的$ a2（第37行，现在硬编码）。此外，我无法弄清楚如何打印写入我的文件的字符数（$ v0包含此值后写入文件，第49行）。

现在程序抛出错误：第49行：0x00400078处的运行时异常：地址超出范围0x0000002c

这是我的代码：

.data

handle_text:
    .space 100 # buffor of 100 characters, bits, bytes?

out_file:
    .asciiz "file_out.txt" # out file

asklabel:
    .asciiz "Please enter string to save
" 

countlabel:
    .asciiz "Characters typed:
"

.text
main:
    la $a0, asklabel # text to print
    li $v0, 4 # opcode
    syscall

    la $a0, handle_text # Where to put text
    la $a1, handle_text # Number of characters to write
    li $v0, 8 # opcode
    syscall 

    li $v0, 13       # system call for open file
    la $a0, out_file     # output file name
    li $a1, 1        # Open for writing (flags are 0: read, 1: write)
    li $a2, 0        # mode is ignored
    syscall            # open a file (file descriptor returned in $v0)
    move $s6, $v0      # save the file descriptor 

    move $a0, $s6 # file handle
    la $a1, handle_text # text to print
#line 37
    li $a2, 44 # TEXT LENGTH
    li $v0, 15 # opcode
    syscall

    move $t1, $v0 # move v0 to t1 so v0 won't be overwritten

    la $a0, countlabel # show text 
    li $v0, 4 # op code
    syscall 

    move $a0, $t1 # place characters amount in $a0
    li $v0, 4 # opcode
    syscall
# ERROR. Maybe it's becouse string should be null terminated?

    li   $v0, 16       # system call for close file
    move $a0, $s6      # file descriptor to close
    syscall            # close file

    li $v0, 10  # close app
    syscall