• What does the code fragment in problem 6.8 do?
• What information does $20 contain at the beginning of the loop?
• Try the problem again using the datapath from Figure 6.44 on page 417 instead of the one on page 386.

So I need advice. Should we buy Sam a game system? If so, do we go for Super Nintendo, Nintendo 64, Sega Genesis, Sega Saturn, or Sony Playstation? If not, on what grounds do we refuse? Thanks for the help.

Some of the questions below concern the addressing modes described in the table at the bottom right of page 31. Some clarification of these modes is in order before you get started. The "#[Rxx]" addressing mode is very much like the second operand of the MIPS instructions lw and sw. Also, "Rxx--" means that the register is decremented after its contents are used as an operand (post-decrement), and "--Rxx" means the register is decremented before it is used (pre-decrement). Thus, for example, "move r14, @--r12" would decrement r12, then get the word pointed to by the new r12, and put that word in r14.

One last note. There are typos aplenty in this paper, and at least a couple of them seem to involve dollar signs. A dollar sign preceding a number indicated that the number is expressed in hexadecimal notation. Otherwise, the base is ten. If you think there should be a dollar sign somewhere where there isn't one, it's probably a typo.

Let's get started.

• In NICE, what is the smallest addressable unit of memory? For MIPS, the smallest addressable unit is one byte, so instruction addresses are multiples of four. What can you say about instruction addresses on NICE?
  
  
• What do the NICE instructions "add r3, r4, r5" and "?!z mov r15, #label" do? Show machine code for each of them.
  
  
• Why are immediate operands important in instruction set design? In NICE, where are immediate operands stored? What range of integers are allowable as immediate operands? What major weakness does NICE have with respect to immediate operands?
  
  
• To what uses might post-increment and pre-decrement addressing modes be put?
  
  
• Consider the multi-cycle datapath of Figure 5.36 on page 315 of Patterson and Hennessy. Either draw a similar datapath or modify Figure 5.36 to make it suitable for implementing the NICE instruction set. You may ignore anything related to interrupts, and you should not concern yourself with the internal structure of the control required to drive your datapath.
  
  
• What do you think NICE's strengths are? How about its weaknesses? The author says that NICE is "well suited for educational purposes as well as for small control applications." For what reasons would NICE be inappropriate for higher performance computing?