* Only need the integer instructions
  <instruct> Rdest, Rsrc1, Src2 where Src2 is immediate or a
    register (addu, subu, divu, multu )

* Load/store
  la Rdest, address         load address into register Rdest
  lw Rdest, address         load value at address into Rdest
  sw Rsrc, address          store word from register Rsrc into
                            address
* Move
  move Rdest, Rsrc          move contents of Rsrc into Rdest

* Control
  b label            branch to label
  beqz Rsrc, label branch to label if value in Rsrc equals 0
  bgeu Rsrc1, Src2, label branch to label if contents of
             register Rsrc1 is greater than or equal to Src2
  similarly bgtu, bleu, bltu
  j label            unconditionally jump to label
  jal label          unconditionally jump to labe and save
     address of next instruction in $ra

* System
   syscall  register $v0 contains number of system call
            print_int      1      $a0 has integer
	    print_float    2      $f12 = float
            print_double   3      $f12 = double
            print_string   4      $a0 has string
            read_int       5      integer result in $v0
            read_float     6      float result in $v0
            read_double    7      double result in $v0
            read_string    8      $a0 buffer, $a1 length
            sbrk           9      $a0 amount
            exit          10

* Pseudoinstructions expand into several machine
  instructions

* registers
   Register      Number                             Usage
      $zero        00   constant 0
      $at          01   reserved for assembler
      $v0          02   expression evaluation and results of a function
      $v1          03   expression evaluation and results of a function
      $a0          04   argument 1
      $a1          05   argument 2
      $a2          06   argument 3
      $a3          07   argument 4
      $t0          08   temporary (not preserved across call)
      $t1          09   temporary (not preserved across call)
      $t2          10   temporary (not preserved across call)
      $t3          11   temporary (not preserved across call)
      $t4          12   temporary (not preserved across call)
      $t5          13   temporary (not preserved across call)
      $t6          14   temporary (not preserved across call)
      $t7          15   temporary (not preserved across call)
      $s0          16   saved temporary (preserved across call)
      $s1          17   saved temporary (preserved across call)
      $s2          18   saved temporary (preserved across call)
      $s3          19   saved temporary (preserved across call)
      $s4          20   saved temporary (preserved across call)
      $s5          21   saved temporary (preserved across call)
      $s6          22   saved temporary (preserved across call)
      $t7          23   saved temporary (preserved across call)
      $t8          24   temporary (not preserved across call)
      $t9          25   temporary (not preserved across call)
      $k0          26   reserved for OS kernel
      $k1          27   reserved for OS kernel
      $gp          28   pointer to global area
      $sp          29   stack pointer
      $fp          30   frame pointer
      $ra          31   return address (used by function call)