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14,210 Views
Registered: ‎03-08-2014

[Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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I am using multiple FSM in my module, Linux , Vivado 2013.3..

 

When I assign every signal in every state (for every FSM avoiding multi-drivers for any signal) to avoid unwanted latchs

I got my whole design optimized away

the module is synthesised empty

what is wrong here?

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Xilinx Employee
Xilinx Employee
16,047 Views
Registered: ‎02-14-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Hi,

You can prevent the optimization of those registers by placing FSM_ENCODING attribute on them.

Please check the snapshot below for further detailsfsm.PNG

By selecting the value "off" for this particular attribute, you will be able to keep the register in the synthesized netlist without optimization.

Regards,
Ashish
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13 Replies
Xilinx Employee
Xilinx Employee
14,203 Views
Registered: ‎02-14-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Can you share the design files so that it will help to debug the issue further?

Regards,
Ashish
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Xilinx Employee
Xilinx Employee
14,198 Views
Registered: ‎07-01-2010

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Hi,

 

Please make sure the state machine driving elements are active (connected ) so that the tool doesn't trim them as unconnected.

 

If you think the code is valid ,try to have the don't_touch attribute on the signals listed as trimming/removed.please share the design in this case.

 

Regards,

Achutha

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14,191 Views
Registered: ‎03-08-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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here is vhdl file

with four FSMs

one controlls the other  three

 after synthesis , two are infered as onehot FSM and the others are ignored

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Xilinx Employee
Xilinx Employee
14,155 Views
Registered: ‎02-14-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Hi @ghada_abozaid 

 

There are certain missing files and package because of which the issue cannot be reproduced. Can you please send the complete files ?

Regards,
Ashish
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Xilinx Employee
Xilinx Employee
14,144 Views
Registered: ‎07-01-2010

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Hi ,

Can you give the details of which state machine is not inferred?
Also please share the synthesis log and the rest of the file to reproduce the issue.

Regards,
Achutha
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14,141 Views
Registered: ‎03-08-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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mac and loading FSM are inferred 

but they are optimized away 

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14,120 Views
Registered: ‎03-08-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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@ashishd here are the sources 

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Xilinx Employee
Xilinx Employee
14,095 Views
Registered: ‎02-14-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Hi,

I have downloaded your design and tried to reproduce the issue.

When I synthesized the project, I am able to see the registers for loading, offloading, MAC and controller FSM without the warning as you have mentioned.

Please check the snapshot of netlist view.   

 

netlist.PNG

 

Can you let me know the value of -fsm_extraction switch in Synthesis Setting dialogue box?

Regards,
Ashish
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14,091 Views
Registered: ‎03-08-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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I tried 

Auto

then gray code

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Xilinx Employee
Xilinx Employee
8,486 Views
Registered: ‎02-14-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Hi,
Were the results similar?
When you select 'auto' for this switch, the tool to choose the best encoding for each state machine identified. In this case, the tool may use different encoding styles for different FSMs in the same design. Can you share the synthesis log?
Regards,
Ashish
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8,483 Views
Registered: ‎03-08-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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using auto or gray fsm extraction was giving me same warnings 

 

But 


I did make small modification in some signals assignment , and the warnings about the FSM gone

but , that make me wonder  How it wored wth you without these modifications? that make me belive that some thing is not right , I could not figure out what!!

 

now I have some registers optimized out 

to priecsism,  two registers 

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Xilinx Employee
Xilinx Employee
16,048 Views
Registered: ‎02-14-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Hi,

You can prevent the optimization of those registers by placing FSM_ENCODING attribute on them.

Please check the snapshot below for further detailsfsm.PNG

By selecting the value "off" for this particular attribute, you will be able to keep the register in the synthesized netlist without optimization.

Regards,
Ashish
----------------------------------------------------------------------------------------------
Kindly note- Please mark the Answer as "Accept as solution" if information provided is helpful.
Give Kudos to a post which you think is helpful and reply oriented.
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8,471 Views
Registered: ‎03-08-2014

Re: [Synth 8-3332] Sequential element (\FSM_onehot_currentState) is unused and will be removed

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Thank you so much @ashishd 

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