9
NO CLASS on
Monday
Oct. 18, 2010
Please read Sections 4.4 and D.2 (on the CD) of the Patterson & Hennessy text.
The control for the single-cycle MIPS datapath involves mapping bits
from the opcode (always) and bits from the function field (sometimes)
into control signals for the various multiplexors, the ALU, the memory,
etc. The text presents this design in bits and pieces, focusing first
on the control of the integer ALU, and then moving on to the other
control signals.
Please consider, but don't bother to write up, your responses to these questions:
1. Why does this scheme not work for the ori instruction?
2. Same question, but for the jr instruction.
Then, be prepared to discuss the following in class:
3. During this class we will explore the text's control design and extend it to cover some instructions not in the subset used in this chapter. If you look closely at the text's scheme you will quickly see that it fails for many non-subset (and non-floating point) instructions, including the two you looked at above. Think about how this control design might be unified into some single coherent structure that could be naturally extended to include the rest of the instructions. You should look at Section B.10, and especially Figure B.10.2, as part of your preparation, and of course sketches of your hardware ideas will be helpful. Please avoid trickery such as doing arithmetic on the opcode! We're in search of a simple, extensible structure.