Program 4: Memory Copy

Program 4: Memory Copy

Reserving Space, Pt. 2 #

Sometimes (read most of the time) you probably won’t know the length of the output or exactly how much space you will need for the program. As opposed to writing a string in memory, you can use the fill directive to reserve space. The syntax is # of data parts to reserve, the size of the space to reserve, and the value to store in that space. If the default value is not provided, it will default to 0 (integer). If you provide the size of each data repeat, it must be 1, 2, or 4 referring number of bytes. If the size is omitted, it is assumed to be 1 (byte).1 There are other ways to reserve memory through the operating system, but they are outside the scope of this course.

label:      .fill   128         @ reserves 128 bytes
label2:     .fill   128, 2, 1   @ reserves 128 2-byte blocks (256 bytes) 
                                @ with each 2-byte value equal to 1

  1. It’s super important to note that with the ARM compiler, the syntax is slightly different. The order of the values is # of blocks, value, size. When in doubt, you can also just use .space in either syntax and provide the number of bytes followed by the fill value you want. (e.g., .space 128, 1 for 128 bytes set to the value 1) ↩︎

Program 4: Memory Copy Video

Description of Program
My friend’s cat is named Summer. I want to tell the whole world his name, but first I need to copy it to send! (Look, coming up with creative prompts is hard. Just do the exercise. 🤫) Using the below starter data section, write a program that will copy the input string and output it to stdout.
Completed Code
Expected Output