Answer from cs61c-cg (Daniel Lau 16776873) for Question 4
memory-mapped io is one type of io system that reads and writes to the memory of the selected address.

la   $t1, 0xffff0000
la   $t2, 0xffff0004
li   $t4, 1
loop: lw  $t3, rcon
      beq $t3, $t1, read
      j   loop
read: 
      sb  $v0, 24($t2)
      j   loop