Quiz submission record for quiz6-2-2 at Wed Jul 28 19:42:07 2004:

Your Answer for Question 1:
The EPC is the exception program counter which holds the address of the instruction that caused the exception.  The Cause register contains a field that can be used to tell what caused the exception. The two control signals that cause the EPC and Cause registers to be written are EPCWrite and CauseWrite. 

Your Answer for Question 2:
Imprecise exceptions are ones whose EPC are not necessarily the program counter of the offending instruction.  It is up to the software to determine what instruction failed.

Your Answer for Question 3:
Polling is bad because I/O devices are very slow compared to the processor.  If the processor must poll a lot, it wastes many cycles that in which it could have been doing something useful.

Your Answer for Question 4:
A memory-mapped I/O means that I/O device is emulated in an address space in the system memory.  (No system data is stored at that address space.)

#while the receiver control register (address 0xffff0000) has a 1 value, get a byte from the receiver (address 0xffff0004).

loop: li $t0, 0xffff0000
      lw $t1, 0($t0)
      andi $t1, $t1, 0x1
      beq $t1, $0, loop:
      lw $v0, 4($t0)


Your unique submission ID is quiz6-2-2-cs61c-cj-1091068927-560.