.text 
    lw $s0, kbdstatus   # enable interrupts
    ori $s0, 2
    sw $s0, kbdstatus
mainloop:               # now loop doing nothing
    nop
    j   mainloop


   .text 0x80000180     # in MARS the ISR must be at this address
isr:
   move $k0, $at        # save $at; needed by assembler for following instrs
   lw   $k1, kbddata    # load the character from kbd
   sw   $k1, dispdata   # display the character (note: not correct; doesn't test display ready) 
   move $at, $k0        # restore #at
   eret                 # return from ISR; re-enables interrupts
   
   .data 0xffff0000
kbdstatus:
   .space 4
kbddata:
   .space 4
dispstatus:
   .space 4
dispdata:
   .space 4