CS 2200 Presentation 4

1
CS 2200Presentation 4

• Datapath

2
drum roll...

• Introducing the

LC-2200
3
LC2200

• The LC is a 32-bit computer with 16 general
  registers plus a separate program counter (PC)
  register. All addresses are word addresses.
  Register 0 is wired to zero it always reads as
  zero and writes to it are ignored.

4
Accessible Registers

• Reg Name Use
  Callee Save?
• ----- ---- -------------------------
  -----------
• 0 zero always zero (by hardware)
  n.a.
• 1 at reserved for assembler
  n.a.
• 2 v0 return value
  no
• 3 a0 argument or temporary
  no
• 4 a1 argument or temporary
  no
• 5 a2 argument or temporary
  no
• 6 a3 argument or temporary
  no
• 7 a4 argument or temporary
  no
• 8 s0 saved register
  YES
• 9 s1 saved register
  YES
• 10 s2 saved register
  YES
• 11 s3 saved register
  YES
• 12 k0 reserved for OS/traps
  n.a.
• 13 sp stack pointer
  YES
• 14 fp frame pointer
  YES
• 15 ra return address
  YES

5
LC-2200 Instruction Set
Assembler Examples add s0, s1, s2 s0 ? s1
s2 nand s0, s1, s2 s0 ? (s1 s2)
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LC-2200 Instruction Set
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LC-2200 Instruction Set
Assembler Examples addi s0, a0, 14 s0 ?
a0 14 lw s0, 8(s1) s0 ? MEMs1
8 sw s0, -4(s1) MEMs1 - 4 ? s0 beq
a0, a1, label if a0a1
PC ? PC 1 Offset
8
Question

• beq s0, s1, label line 1
• add a0, a1, a2
• nand s2, s3, a3
• label
• addi s1, s1, 6
• What value is in the offset field of the
  instruction generated in line 1?

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LC-2200 Instruction Set
Assembler Examples jalr s0, ra ra ? PC
1 PC ? s0 jalr s0, s0 s0 ? PC 1
PC ? s0 (PC 1) jalr ra, zero PC ? ra
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LC-2200 Instruction Set
Function
Halt processor
Do nothing
31 28
27 24
23 20
19 0
Op Code
Unused
Assembler Examples halt Stop
execution
11
LC-2200 Pseudo-Ops
Assembler Examples nop Do
nothing .word 32 Fill current
location with 32 .word label Fill
current location with value
of the symbol "label"
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More Assembler Examples

• Add A and B and put result in C
• start lw a0, A(zero)
• lw a1, B(zero)
• add a0, a0, a1
• sw a0, C(zero)
• A .fill 42
• B .fill 37
• C .fill 0

13
More Assembler Examples
Loop until a0 0

• loop beq a0, zero, break
• addi a0, a0, -1
• beq zero, zero, loop
• break

0x0030 0x53000002 0x0031 0x233fffff 0x0032
0x500ffffd 0x0033
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More Assembler Examples

• start lw a0, A(zero)
• lw a1, B(zero)
• addi s0, zero, addem
• jalr s0, ra
• sw v0, C(zero)
• halt
• addem add v0, a0, a1
• jalr ra, zero
• A .fill 27
• B .fill 92
• C .fill 0

15
What's Missing?

• How do you do a NOP?
• How do you subtract?
• How do you branch on an inequality? (e.g. BLT)
• Multiply/divide/shifts
• Data types other than 32-bit words?

16
Questions?
17
Five Classic Components
Recall
Processor
Memory
Control
Datapath
18
Lets take a closer look...
Processor
Control
Datapath
19
Big Picture

• Fetch the instruction from memory
• Decode the instruction and decide what to do
• Execute the instruction
• Repeat.
• What do we need to add 2 registers together and
  store the result in a third?

20
LC-2200 Datapath
PC
21
LC-2200 Datapath
PC
22
LC-2200 Datapath
PC
IR
23
LC-2200 Datapath
PC
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
24
LC-2200 Datapath
PC
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
A
LdA
25
LC-2200 Datapath
PC
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
A
B
LdB
26
LC-2200 Datapath
PC
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
A
B
LdA
LdB
2
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
27
QuestionDid you understand the preceding
explanation of adding?

• 1 Crystal Clear
• 2 Sort of
• 3 We were adding?

28
PC
Consider the LW instruction lw s0, 4(s1)
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
A
B
LdA
LdB
2
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
29
PC
Consider the LW instruction lw s0, 4(s1)
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
A
B
LdA
LdB
2
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
30
MAR
PC
Consider the LW instruction lw s0, 4(s1)
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
A
B
LdA
LdB
2
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
31
MAR
PC
Consider the LW instruction lw s0, 4(s1)
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
A
B
LdA
LdB
2
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
32
Making it more real...

• This is getting very complicated!!!
• For reasons involving implementation details, the
  simplest (lowest cost, lowest performance)
  technique is to use a single bus to connect all
  the various functional units

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Bus
Functional Unit
Functional Unit
Functional Unit
Functional Unit
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BusOnly One Functional Unit at a time can drive
bus
Functional Unit
Functional Unit
Functional Unit
Functional Unit
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BusAny (and all) functional units can access bus
Functional Unit
Functional Unit
Functional Unit
Functional Unit
36
Question

• What happens if two functional units try to drive
  the bus at the same time?
• Data is corrupted
• Smoke and possibly flames issue forth
• Processor shuts down
• Core dump

37
Questions?
38
LC-2200 Datapath
32
A
LdA
B
LdB
10
memory 1024x 32 bits
Addr Din
registers 16x 32 bits
Din
IR31..0
WrREG
WrMEM
2
4
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
IR19..0
regno
20
Dout
Dout
sign extend
0?
RA 4-bit register number to control logic
IR27..24
1
RB 4-bit register number to control logic
IR23..20
RD 4-bit register number to control logic
IR3..0
OP 4-bit opcode to control logic
IR31..28
1
Z 1-bit boolean to control logic
39
Recall our basic add instruction
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LC-2200 Datapath
PC
registers 16x 32 bits
Din
WrREG
4
?
IR
regno
Dout
A
B
LdA
LdB
2
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
Did we leave anything out?
41
Need to increment PC!
42
LC-2200 Datapath
32
A
LdA
10
memory 1024x 32 bits
Addr Din
registers 16x 32 bits
Din
IR31..0
WrREG
WrMEM
2
4
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
IR19..0
regno
20
Dout
Dout
sign extend
0?
RA 4-bit register number to control logic
IR27..24
1
RB 4-bit register number to control logic
IR23..20
RD 4-bit register number to control logic
IR3..0
OP 4-bit opcode to control logic
IR31..28
1
Z 1-bit boolean to control logic
43
LC-2200 Datapath
32
A
LdA
10
memory 1024x 32 bits
Addr Din
registers 16x 32 bits
Din
IR31..0
WrREG
WrMEM
2
4
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
IR19..0
regno
20
Dout
Dout
sign extend
0?
RA 4-bit register number to control logic
IR27..24
1
RB 4-bit register number to control logic
IR23..20
RD 4-bit register number to control logic
IR3..0
OP 4-bit opcode to control logic
IR31..28
1
Z 1-bit boolean to control logic
44
LC-2200 Datapath
32
A
LdA
10
memory 1024x 32 bits
Addr Din
registers 16x 32 bits
Din
IR31..0
WrREG
WrMEM
2
4
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
IR19..0
regno
20
Dout
Dout
sign extend
0?
RA 4-bit register number to control logic
IR27..24
1
RB 4-bit register number to control logic
IR23..20
RD 4-bit register number to control logic
IR3..0
OP 4-bit opcode to control logic
IR31..28
1
Z 1-bit boolean to control logic
45
LC-2200 Datapath
32
10
memory 1024x 32 bits
Addr Din
registers 16x 32 bits
Din
IR31..0
WrREG
WrMEM
2
4
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
IR19..0
regno
20
Dout
Dout
sign extend
0?
RA 4-bit register number to control logic
IR27..24
1
RB 4-bit register number to control logic
IR23..20
RD 4-bit register number to control logic
IR3..0
OP 4-bit opcode to control logic
IR31..28
1
Z 1-bit boolean to control logic
46
LC-2200 Datapath
32
10
memory 1024x 32 bits
Addr Din
registers 16x 32 bits
Din
IR31..0
WrREG
WrMEM
2
4
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
IR19..0
regno
20
Dout
Dout
sign extend
0?
RA 4-bit register number to control logic
IR27..24
1
RB 4-bit register number to control logic
IR23..20
RD 4-bit register number to control logic
IR3..0
OP 4-bit opcode to control logic
IR31..28
1
Z 1-bit boolean to control logic
47
LC-2200 Datapath
32
10
memory 1024x 32 bits
Addr Din
registers 16x 32 bits
Din
IR31..0
WrREG
WrMEM
2
4
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
IR19..0
regno
20
Dout
Dout
sign extend
0?
RA 4-bit register number to control logic
IR27..24
1
RB 4-bit register number to control logic
IR23..20
RD 4-bit register number to control logic
IR3..0
OP 4-bit opcode to control logic
IR31..28
1
Z 1-bit boolean to control logic
48
LC-2200 Datapath
32
10
memory 1024x 32 bits
Addr Din
registers 16x 32 bits
Din
IR31..0
WrREG
WrMEM
2
4
ALU 00 ADD 01 NAND 10 A - B 11 A 1
func
IR19..0
regno
20
Dout
Dout
sign extend
0?
RA 4-bit register number to control logic
IR27..24
1
RB 4-bit register number to control logic
IR23..20
RD 4-bit register number to control logic
IR3..0
OP 4-bit opcode to control logic
IR31..28
1
Z 1-bit boolean to control logic
49
Basic Algorithm

• Lather
• Rinse
• Repeat

50
Question

• I understand the basic operation of the LC-2200
  datapath
• Very well, sir, may I have another!
• Sorta, kinda
• A clue
• Somewhat confused
• Lost in the jungles of Borneo

51
Questions?
52
(No Transcript)