Answer from cs61c-en (Lai, Siu Lun Chris 16529329) for Question 4
It means that when spim is running, it reads the characters that the user types and writes the character on the terminal.

       li $t0 0xffff0004
Loop:  lw $t1 0($t0)
       bneq $t1 $0 EXIT
       addi $t0 $t0 4
       j Loop
EXIT:  mov $v0 $t1