Computer Science 237 Computer Organization Williams College Fall 2006

Agenda

• Announcements
  • Be a Computer Science teaching assistant for the spring semester! See Lorraine Robinson in the CS office or fill out the online form to apply. The deadline is November 28.
  • Formal lab meetings are done. I highly recommend using those time slots to work on your design projects.
  • Tear down memory circuits and clean up if you have not already done so
  • Demonstrate working or partial implementation of the bonus lab by today also
• Back to Tanenbaum's Microcode - see previous lecture
• WC34000 Implementation project
  • How bad can it be, given this description from a recent student?
  • Administrative notes:
    • work on phase 1 individually
    • work on phases 2 and 3 alone or in pairs
    • in either case - appropriate permissions and version control is essential (interest in an optional lab session to learn the subversion source code control system?)
  • Microcode design project is to implement the WC34000 computer on the Mice microarchitecture
  • The 34000 is a simplified 68000-like computer - more on that later
  • The Mice microarchitecture
    • Based closely on Tanenbaum's Mic1
    • Larger scratchpad - 31 registers
      • important because we need 16 general purpose registers plus things like a PC and an IR when we implement the 34000
      • can define names for registers or refer by numbers - you should define names for all of the registers you use
      • register pointer - use when 31 is the register number
      • MPC is always in R[30] - this is useful in some contexts we will see soon
    • A/B buses as in Mic1
    • Extra ALU functions - we can multiply, divide, subtract, bor
    • Shifter does rotate left 8 bits in addition to one-bit shifts from Mic1
    • There is an extra bus, the X bus, parallels the A and B bus.
    • Contents of the bus are controlled by an X address (5 bits), as well as an additional bit of ALU function.
    • If the function bit is one (1), the register indicted by the X address is loaded onto the X bus. All the usual interpretations apply: if the address is 31, it loads R[RP], etc.
    • If the function bit is zero (0), the X address (a value between 0 and 31) is loaded onto the X bus.
    • The A and B bus are combined as indicated by the architecture document: A, inv(A), A+B, A-B, band(A,B), bor(A,B), A*B, or A/B.
    • The result of combining A and B is always combined with X. Thus we can compute inv(A)+#1, or A*B+X, etc.
    • The result of combining all three buses is fed to the shifter where it is possible to perform lshift, rshift, rotate8, or leave unaltered.
    • The micro-assembler attempts to do the right thing. Thus, A+B sets the X address and function bits both to zero (0).
      Performing

          male -b phase2.bits phase2.mal
        

      Will show you the details; the function bit described is bit 3 of the ALU bits.
  • Microcode notes
    • Your microcode may be up to 1024 microinstructions long
    • At the start of your microprogram (when you run mice), only one register has a known value - the MPC is 0
    • can use semicolons to reserve slots for future use
  • A few example microprograms (in /usr/cs-local/share/cs237/examples/ucode)
    • justhalt
    • makeazero - how can we get a 0?
    • makeaten - how can we get a 10?
    • registers
    • make42bad
    • make42
  • The WC34000 Computer
  • 34000 assembly examples in /usr/cs-local/share/cs237/ucode