Quiz submission record for quiz6-2-2 at Wed Jul 28 21:21:33 2004:

Your Answer for Question 1:
EPC: A 32-bit register used to hold the address of the affected instruction.

Cause: A register used to record the cause of the exception.

These registers are accessed by the lwc0, mfc0, mtc0, and swc0 instructions.

Your Answer for Question 2:
Since it is sometimes difficult to associate the correct exception with the correct instruction, some computers relax that requirement in noncritical cases. This is known as imprecise exceptions. A machine with imprecise exceptions may give the EPC an address and leave it up to the operating system to figure out which instruction actually caused the problem.

Your Answer for Question 3:
The main problem with polling is that it can waste a lot of processor time because processors are much faster than I/O devices. The processor may read the Status register many times, only to find out that the device has not yet completed a slow I/O operation or not even changed since the last time it was polled.

Your Answer for Question 4:
A program controls the SPIM terminal with four memory-mapped device registers. Memory-mapped means that each register appears as a special memory location.

la $t0, 0(0xffff0000)
la $t2, 0(0xffff0004)
la $v0, 0(some address with a buffer)
lb $t1, 0($t0)
loop:
beq $t1, 0, exit
sb $t2, 0($v0)
addi $v0, $v0, 1
j loop
exit:


Your unique submission ID is quiz6-2-2-cs61c-ev-1091074893-2506.