Quiz submission record for quiz6-2-2 at Wed Jul 28 21:29:48 2004:

Your Answer for Question 1:
EPC register holds the memory address at which the interrupt/exception occured.  The cause register is used to indicate the type of exception.  The cause register is accessed using mfco and the EPC is accessed only by the processor, not the user.

Your Answer for Question 2:
Imprecise exceptions are of unknown type.  For example, some processors do not specify the type of exception because it is easier to implement a processor in this fashion.

Your Answer for Question 3:
The drawback of polling is that the processor must continually check the bit that indicates that the data from the I/O device has changed, which takes time because the processor must access the device.

Your Answer for Question 4:
memory-mapped io means that each register appears as a special memory location.  When information is typed into the console, it is written to a special memory location that the programmer cannot use that the processor uses to fetch data from the keyboard.

     li   $t0, 0xffff0000 #recv ctrl
     addi $t1, $t0, 4  #recv data
     addi $t2, $t1, 4  #trans ctrl
     addi $t3, $t2, 4  #trans data
     
poll:lw $t4, 0($t2)
     bne $t4, $0, write
     j poll
write: sw $v0, 0($t3)
       j poll 


Your unique submission ID is quiz6-2-2-cs61c-an-1091075388-2215.