CBP 2009Comp 3014 The Nature of Computing 1 Laundry Model Washer Drier Store Basket Wardrobe.
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CBP 2009 Comp 3014 The Nature of C omputing 1 Laundry Model Washer Drier Store Basket Wardrobe
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Transcript of CBP 2009Comp 3014 The Nature of Computing 1 Laundry Model Washer Drier Store Basket Wardrobe.
CBP 2009 Comp 3014 The Nature of Computing
1
Laundry Model
Washer Drier Store Basket Wardrobe
CBP 2009 Comp 3014 The Nature of Computing
2
Process Steps
Wash then Dry
1 load takes 2 hours
idle
idle running
running
time
time
9.00 10.00 11.00
1. Load the washer at 9.00
2. Done at 10, load the drier
3. Drier Done at 11
0.5
CBP 2009 Comp 3014 The Nature of Computing
3
Sequential Process
3 loads takes 6 hours
time
9.00 15.00 11.00
1. Load washer at 9.00
2. Done at 10, load drier
3. Drier Done at 11
4. Reload washer at 11
5. Done at 12, load drier
6. Drier done at 13
7. Reload washer at 13
8. Done at 14, load drier
9. Done at 15
13.00
0.5
CBP 2009 Comp 3014 The Nature of Computing
4
Overlapping Process
3 loads takes 4 hours
time
9.00 15.00 11.00
1. Load washer at 9.00
2. Done at 10, load drier reload washer
3. Both Done at 11. Reload drier reload washer
4. Both done at 12. Reload drier
5. Drier done at 13
13.00
From 10.00 till 11.00 both washer and dryer running concurrently
0.75
CBP 2009 Comp 3014 The Nature of Computing
5
Washing Pipeline Filling
time
9.00 11.00 13.00 15.00 17.00
18.00
5 loads in 9 hours
5 Cycles !!!1. Get
washing2. Wash3. Dry4. Store5. Put away
0.55
CBP 2009 Comp 3014 The Nature of Computing
6
Washing Pipeline Fulltime
9.00 11.00 13.00 15.00 17.00
Pipe Full gives 1 load per hour 1.0
CBP 2009 Comp 3014 The Nature of Computing
7
Can we Pipeline SAM ?
Data Memory
Instruction reg
Code Memory
ALU
r1
r2
r0X
Y
W
X Y
W
0
1
7mar
mdr
1.Fetch
2.Dec/Reg
3.ALU 4.Mem
5.RW
CBP 2009 Comp 3014 The Nature of Computing
8
Pipelined Sam4
Data Memory
0
1
7
X
Y
W
Y
W
r1
r2
r0
X
Code Memory
1.Fetch
2.Dec/Reg
3.ALU 4.Mem 5.RW
Buffer
time
CBP 2009 Comp 3014 The Nature of Computing
9
5 Stages in Pipeline
AL
UMem Reg Mem Reg
add r3,r1,r2 r1,r2 r3add
Let’s take the instruction add r3,r1,r2 and show which stage is needed for each part of the instruction.
1.Fetch 2.Dec/Reg
3.ALU 4.Mem 5.RW
time
CBP 2009 Comp 3014 The Nature of Computing
10
ld r0 Mem r3
Two Instructions
ld r3,[r0+2]
Two instructions into the pipeline
add r4,r1,r2 AL
Uadd r1,r2 r4
r0
2
time
CBP 2009 Comp 3014 The Nature of Computing
11
Structural Hazard
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
Here we are being asked to read from memory and write to it simultaneously. Impossible!
Write (store)
Read (fetch
)
Solution – Use separate code and data memories
add r4,r1,r2
st r0,[5]
CBP 2009 Comp 3014 The Nature of Computing
12
Hazardous Washing
time
9.00 11.00 13.00 15.00 17.00
18.00
Washing basket containes both clean and dirty
washing!
CBP 2009 Comp 3014 The Nature of Computing
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Code and Data Memories
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
CBP 2009 Comp 3014 The Nature of Computing
14
add r1,r2 r3
Data Hazard
add r3,r1,r2
but need r3 here
EARLIER !
add r4,r1,r3 add r1,r3 r4
r3 set heretime
CBP 2009 Comp 3014 The Nature of Computing
15
Data Hazard
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
add r3,r1,r2
add r4,r1,r3
Need value of r3 for second instruction before the first is complete.
CBP 2009 Comp 3014 The Nature of Computing
16
Pipeline Stalls
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
AL
UMem Reg Mem Reg
Mem
AL
UReg Mem RegStall Stall
AL
UMem Reg Mem Reg
add r3,r1,r2
add r4,r1,r3
Resolve Hazard – Insert delay into second instruction stream. ‘Stall’ Cycles.
But this needs extra electronics on the chip. Complex and Costly.
