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Visitor sneha22
Visitor
9,784 Views
Registered: ‎01-17-2011

WARNING:Xst:2170

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HI,

 

I am getting this warning though I have not created too many case states .There are only 4 case statements.

 

 

WARNING:Xst:2170 - Unit RS232_TX : the following signal(s) form a combinatorial loop: next_state<3>.
WARNING:Xst:2170 - Unit RS232_TX : the following signal(s) form a combinatorial loop: next_state<2>.
WARNING:Xst:2170 - Unit RS232_TX : the following signal(s) form a combinatorial loop: next_state<1>.
WARNING:Xst:2170 - Unit RS232_TX : the following signal(s) form a combinatorial loop: next_state<0>.
What danger does it pose to the block of the code?
I dont know why i am getting this warning?

 

 

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Mentor awillen
Mentor
12,837 Views
Registered: ‎11-29-2007

Re: WARNING:Xst:2170

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@bassman59 wrote:

 


@sneha22 wrote:
solved it..

And your solution was ... ??

 


...probably not to create a combinational loop.

 



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7 Replies
Mentor awillen
Mentor
9,782 Views
Registered: ‎11-29-2007

Re: WARNING:Xst:2170

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The warnings you get have nothing to do with you having too many states (what makes you think that?). The real reason is that you did not use proper synchronous digital design techniques: your signal next_state is read and written to in a combinational circuit.

To see how a state machine has to be coded, open the Language Temples ==> Verilog/VHDL ==> Synthesis constructs ==> Coding examples ==> State machines.

Better yet, buy a book on your favorite HDL and read it thoroughly.

 

 

Adrian



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Visitor sneha22
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9,751 Views
Registered: ‎01-17-2011

Re: WARNING:Xst:2170

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solved it..
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Historian
Historian
9,742 Views
Registered: ‎02-25-2008

Re: WARNING:Xst:2170

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@sneha22 wrote:
solved it..

And your solution was ... ??

 

----------------------------Yes, I do this for a living.
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Mentor awillen
Mentor
12,838 Views
Registered: ‎11-29-2007

Re: WARNING:Xst:2170

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@bassman59 wrote:

 


@sneha22 wrote:
solved it..

And your solution was ... ??

 


...probably not to create a combinational loop.

 



Please google your question before asking it.
If someone answers your question, mark the post with "Accept as solution". If you see a particularly good and informative post, consider giving it Kudos (the star on the left).
Visitor sneha22
Visitor
9,708 Views
Registered: ‎01-17-2011

Re: WARNING:Xst:2170

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i was bymistake changing the state of the fsm outside the clk process..silly one ...
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Visitor melika
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9,098 Views
Registered: ‎10-20-2011

Re: WARNING:Xst:2170

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hello,
i have this warning in ISE 10.1, but it does not write any signals that form a combinatorial loop??!!
how i can find that signals?
thanks.

WARNING Xst :2170 :the following signal(s) form a combinatorial loop:warning.png

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Observer mrovin
Observer
8,465 Views
Registered: ‎12-27-2012

Re: WARNING:Xst:2170

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If you don't see the signal involved in the combinational loop, it is just because you are viewing the design summary window. But if you switch to console or warnings panes (at the bottom of the main window) you will see the same messages but with the list of involved signals. Hope this helps.

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