Answer from cs61c-eb (Dae-Yeon Kim 16568138) for Question 4
Memory-mapped io means that portions of the address space are assigned to io devices.  Reads and writes to those addresses are interpreted as commands to the io devices.

loop:
li $t0, 32'b11
lw $t0, 0xffff0000
li $t1, 0x8
lw $t1, 0xffff0004
li $t0, 32'b11
lw $t0, 0xffff0008
li $t1, 0x8
lw $t1, 0xffff000c
j loop