6 December

1
6 December

• 2 classes to go
• Lego Lab Assistant?
• Questions?
• CCR at end of class today

2
Questions

• Why cant some numbers be represented in floating
  point? How to tell? 11 is OK, why not 1.1?
• How does that control stuff work?

3
Simplified R-type Datapath
Implementing a R-type operation is simply a
matter of routing signals to the right places at
the right times.
ALU Operation
3
5
Read Reg. 1
Inst Bits 25-21
32
data 1
5
Read Reg. 2
Inst Bits 20-16
5
Write Reg.
Inst Bits 15-11
32
data 2
32
Write Data
RegWrite
4
This complex one does the same thing!
5
Control

• Dont lose the forest!
• Each line is a set of wires transporting bits (1
  wire per bit)
• Control signal to each MUX determines which way a
  signal will go
• The control lines all go back to the CONTROL
  block (our FSM)
• The FSM drives these lines at just the right
  times to route signals

6
Representation

• What is 0x8FEFC000 if it represents
• A 2s complement integer?
• An unsigned integer?
• A float?
• An instruction?

7
Representation

• What is 0x8FEFC000 if it represents
• A 2s complement integer?
• The sign bit is 1, so this is a negative number.
  We first take its twos complement.
• A 1000 1111 1110 1111 1100 0000 0000 0000
• A 0111 0000 0001 0000 0100 0000 0000 0000
• 230 229 228 220 214
• 1,073,741,824 536,870,912 268,435,456
  1,048,576 16,384
• 1,880,113,152
• A 1,880,113,152
• An unsigned integer?
• A float?
• An instruction?

8
Representation

• What is 0x8FEFC000 if it represents
• A 2s complement integer?
• An unsigned integer?
• A 8FEFC000
• 8 167 15 166 14 165 15 164 12
  163
• 2,147,483,648 251,658,240 14,680,064
  983,040 49,152
• 2,414,854,144
• A float?
• An instruction?

9
Representation

• What is 0x8FEFC000 if it represents
• A 2s complement integer?
• An unsigned integer?
• A float?
• s 1
• exponent 0001 1111 31
• significand 110 1111 1100 0000 0000 0000
• (1)S (1 significand) 2 (exponent127)
  1x1.1101 1111 1x296
• 1 (1 13 161 15 162 29)
  296
• 1.873 296
• 2.364 1029
• An instruction?

10
Representation

• What is 0x8FEFC000 if it represents
• A 2s complement integer?
• An unsigned integer?
• A float?
• An instruction?
• Opcode (6 bits) 100011 lw
• RS (5 bits) 11111 31
• RT (5 bits) 01111 15
• Address (16 bits) 1100 0000 0000 0000
• Address is negative so 2s complement is 0100
  0000 0000 0000
• Address -214 -16384
• LW 15, -16384(31)

11
Quick Review

• Performance
• Assembly language programming
• Representation
• Arithmetic
• Logic gates
• Multiplication/Division
• Floating Point
• Control
• Pipelining
• Cache
• VM
• I/O, Interrupts, OS

12
What is next in courses?

• Comp 160 Digital Logic (next semester!)
• Comp 140 Compilers
• Comp 142 Operating Systems
• Comp 130 Files and Databases
• Comp 181 Models of Language and Computation

13
Classes to go
1