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Best FSM State Encoding for Low-Power Design

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omara007

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state encoding

Hi Guys

What is the best FSM State Encoding for Low-Power design ? and Why ?
 

vlsi123

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low power rtl design,coding techniques

Hi,

Flip flop toggling will consume more power.
The best state encoding to use depends on application.

1. To reduce the power, the state representations in the FSM are replaced by Gray Code. Gray code only changes one bit at a time, hence, power consumption can be reduced.

2. One hot yet another coding technique for low power. But requires more number of bits, more area. usefull for describing the bus protocols.

3. The latest is partioned FSM architecture. It is best suited to model the low power RTL Design.

https://asicdigitaldesign.wordpress.com/category/low-power/

Thanks,
Vlsi123
 

omara007

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vlsi123 said:
Hi,

Flip flop toggling will consume more power.
The best state encoding to use depends on application.

1. To reduce the power, the state representations in the FSM are replaced by Gray Code. Gray code only changes one bit at a time, hence, power consumption can be reduced.


I guess Gray Code is not always a good choice for low-power FSM .. the reason is as you said depending on the FSM itself .. for example:
State-0: 000
State-1: 001
State-2: 011
State-3: 010

What if there is a transition from state-0 to state-2 ?? .. 2 bits will be toggled .. not only one ..


vlsi123 said:
2. One hot yet another coding technique for low power. But requires more number of bits, more area. usefull for describing the bus protocols.

3. The latest is partioned FSM architecture. It is best suited to model the low power RTL Design.

https://asicdigitaldesign.wordpress.com/category/low-power/

Thanks,
Vlsi123

Can you explain the portioned FSM architecture ?
 

vlsi123

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Yes. u r right. So it depends on your design. If your design has more transitions to immediate above or below levels, then gray will be good.

If u use one hot encoding, always 2 bits toggles if u change to any state. so it looks somewhat consistent.

If your design is very complex, it has more than 50 to 100 states then, u can go for partioned fsm.

The partitioned fsm style is explained in the link i provided above.

Thanks,
Vlsi123
 

Nir Dahan

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