Some MIPS Instructions

• Program 1, to start coding.
• We will use mars as a programming environment.
  • Java based, so it should work everywhere.
  • Installed on the linux machines.
  • Editor, simulator ...
• A some rules of thumb
  • Write c code, then try the assembly
  • Copy the examples you have been given for templates.
  • Don't discard something unless you know what you are throwing away.
  • Use lots of comments
  • Use lots of whitespace
  • When in doubt, program it.
• A quick assembly overview (more later)
  • # starts a comment, to the end of the line
    • Use many many comments, one per line might not be bad
  • Memory is split into multiple sections
    • This is done with assembly dirctives. (HELP, Directives)
    • .data starts the data segment, where data is stored, more later
    • .text starts the text segment, where the program is stored, more later.
    • These can be interspersed, but DO NOT DO THIS.
  • Data types for the data segment

    • label:  .type value 
      	     

    • .word store the values on word boundaries
      • One or more values can be stored (case of array)
      • decimal, or hex.
    • .asciiz stores a string with a null terminator.
      • Because of word order issues, the string will be backwards by word.
    • .space n : reserve n bytes of space.
  • Two other directives
    • .global id makes id globally available (we do this with main)
    • .align 2 forces word alignment.
      • MIPS expects words to start at addresses that end in 00 (or multiples of 4)
      • .align 2 enforces word alignment.
      • MARS doesn't allow this in a text segment, but your authors use it (page A-7)
  • Instructions

    • label:   opcode operand1, operand1, operand3
      	     

    • lw $s1, val1
      • THIS IS NOT THE LW from the green sheet, why not?
      • Look what instructions are generated...
    • add $s3, $s2, $s1
    • System calls:
      • Provide I/O and other operating system services.
      • HELP->Syscalls
      • Load the service number into $v0
      • Load the data into the correct $a registers
      • syscall
    • li $v0, 1
      • Actually addiu but we know about that.
    • move $a0, $s1
      • actually addu
    • la $a0, plus
      • Load the value of the address into the register
      • LUI again.
  • Please note tye syscall to function 10 at the end