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*. *. The ADDF is Next to Complete. The changes are noted in Red. Question ADDF will try to write back. Why can it not do this now?. 2. Function Unit Status. FU. Busy. Op. Dest. Sop1. Sop2. Unit1. Unit2. Rdy1. Rdy2. 1[i]. N. 2[*1]. Y. Mult. F0. F2. F4. No. Yes.

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Presentation Transcript
slide1

*

*

The ADDF is Next to Complete.

The changes are noted in Red.

Question

ADDF will try to write back. Why can it not do this now?

2. Function Unit Status

FU

Busy

Op

Dest

Sop1

Sop2

Unit1

Unit2

Rdy1

Rdy2

1[i]

N

2[*1]

Y

Mult

F0

F2

F4

No

Yes

3[*2]

N

4[+]

Y

Add

F6

F8

F2

5[/]

Y

Div

F10

F0

F6

2[*1]

No

Yes

answer
Answer

ADDF tries to write back to F6, but since the DIVF instruction has not yet read its operands (WAR), the scoreboarding technique will stall the write back until DIVF has read its operands.

slide3

*

*

*

*

The MULTF Finally Completes.

The changes are noted in Red.

2. Function Unit Status

FU

Busy

Op

Dest

Sop1

Sop2

Unit1

Unit2

Rdy1

Rdy2

1[i]

N

2[*1]

Y

Mult

F0

F2

F4

3[*2]

N

4[+]

Y

Add

F6

F8

F2

5[/]

Y

Div

F10

F0

F6

2[*1]

No

Yes

slide4

*

*

The MULTF Writes Results.

The changes are noted in Red.

2. Function Unit Status

FU

Busy

Op

Dest

Sop1

Sop2

Unit1

Unit2

Rdy1

Rdy2

1[i]

N

2[*1]

N

3[*2]

N

4[+]

Y

Add

F6

F8

F2

5[/]

Y

Div

F10

F0

F6

Yes

Yes

slide5

The DIVF can now read its operands.

The changes are noted in Red.

2. Function Unit Status

FU

Busy

Op

Dest

Sop1

Sop2

Unit1

Unit2

Rdy1

Rdy2

1[i]

N

2[*1]

N

3[*2]

N

4[+]

Y

Add

F6

F8

F2

*

*

5[/]

Y

Div

F10

F0

F6

*

*

slide6

The ADDF writes results and DIVF starts.

The changes are noted in Red.

2. Function Unit Status

FU

Busy

Op

Dest

Sop1

Sop2

Unit1

Unit2

Rdy1

Rdy2

1[i]

N

2[*1]

N

3[*2]

N

4[+]

N

5[/]

Y

Div

F10

F0

F6

*

*

slide7

The DIVF will finish execution and write its results. The changes are noted in Red.

2. Function Unit Status

FU

Busy

Op

Dest

Sop1

Sop2

Unit1

Unit2

Rdy1

Rdy2

1[i]

N

2[*1]

N

3[*2]

N

4[+]

N

5[/]

N