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Newbie iljong
Registered: ‎08-15-2013

same source, different result



now I'm using kintex7,


I have a problem with that.


Whenever I make a  bit file, the bit file is so different with same RTL, ucf, constraint.


for example, I implemented I2C module in my design,


I can access all my register & memory address with the I2C.


Sometimes I can not access specific address with the I2C when I use a different bit file


But the bitfile is made with same RTL, ucf, constraints.


I can accept if the change is minor.


But it is critical for my design.


do you have a problem like me??


or have a solution??



1. Bit file is changed whenever I synthesize & implement with same source.

2. How can I fix this problem??


Thank you



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4 Replies
Xilinx Employee
Xilinx Employee
Registered: ‎07-23-2012

Re: same source, different result

If you haven't made even a small change to the RTL then the .bit file should be the same.

Here are the few things that you can check-

1) Make sure that you use the same synthesis/implementation settings on both the runs.
2) Compare the both the .bit files using .hex editor tool or generate .rbt file (from bitgen settings) and compare them. Ideally both the bit files should be one and the same. If not then there is an issue with the tool.
3) As a final step, you can compare the report/log files of synthesis and implementation processes. This tells us which process is deflecting.

Please mark the post as "Accept as solution" if the information provided answers your query/resolves your issue.

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Newbie iljong
Registered: ‎08-15-2013

Re: same source, different result

I checked tool verision & options


everything is same.


I did syn & pnr twice back to back without change.


But sometimes, one is ok, another one is bad. (some module in my design do not work normally)


I'm doubtful about P&R.


P&R time changes whenever I make bit file.


Thank you



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Teacher rcingham
Registered: ‎09-09-2010

Re: same source, different result

There is a header in the .BIT file which includes a timestamp. This will change between runs with the same input. The rest of the file should be the same, though.

How are you comparing the files?

"If it don't work in simulation, it won't work on the board."
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Observer vjose
Registered: ‎08-01-2012

Re: same source, different result

Hi ,


Can you clean the project before you build the bit file.


Can you check if all the contraints are correctly set ?.


Do you generate different frequency from the DCM ?.


Do you use any asyncronous reset ?.


Last two can be the cause . May the bit file is same but its working is different every time you flash the bit file .


With regards


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