Quiz submission record for quiz6-2-2 at Thu Jul 29 03:09:24 2004:

Your Answer for Question 1:
EPC register holds the address which the instruction crashed at. It is PC-4. Cause register holds why it had an exception and the cause. EPC and Cause are both in the coprocessor's register.
mfc0 $3, $13 #Cause is in coprocessor register 13
mfc0 $4, $14  #EPC is in coprocessor register 14

Your Answer for Question 2:
Imprecise exceptions is where in a noncritical case address and cause are a bit vague and they are NEAR the correct reason why exception was thrown. EPC might be off by 4 because it didn't subtract four or it might be worse and be recorded only when the exception hits write back. Cause register might not be matched correctly. 

Your Answer for Question 3:
Polling might draw a lot of processor time because it must keep polling or checking the status bit to see if the I/O device has been touched, changed, or updated. Polling is a continous act and so even when the keyboard has not been hit for a while it will still check to see if it has over and over again.

Your Answer for Question 4:
memory-mapped io means that the input and output are operated with the help of memory. For example, keyboard inputs are written to registers and another registers will show whether the data is ready for another input or not and transfering input from keyboard to output uses another register. In a way the input and output of the keyboard and display is mapped and controlled using memory.

loop: li $t0, 0xffff0000
      li $t1, 1
      lw $t2, 0($t0)
      beq $t2, $t1, poll:
      j loop
poll: li $t3, 0xffff0004
      lbu $v0, 3($t3)
      j loop


Your unique submission ID is quiz6-2-2-cs61c-aj-1091095764-2875.