Answer from cs61c-fz (Sean Nyberg 16014383) for Question 4
Memory mapped I/O is an I/O scheme in which portions of address space are assigned to I/O devices and reads and writes to those addresses are interpreted as commands to the I/O device.

Loop: la $t0, 0xffff0004
      lb $v0, 0($t0)
      beq $0, $0, Loop