Answer from cs61c-eg (Ramanarayan Vasudevan 15938560) for Question 4
Portions of the address space are assigned to io devices and reads and writes to those addresses are interpreted as commands to the IO device. 
loop: la $t0, 0xffff0000
        lbu $t1, 0($t0)
        beq $t1, $0, loop
        move $t1, $v0