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Why would assigning a signal as a Global Clock Signal send board into reset?

DMAHM1
Beginner
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I have a signal which I generate in my design and then use as an input to many LUTs. I wanted to route it through the global clock buffers to save on the routing resources and perhaps lower the compilation time. However, as soon as I try to program the board with this configuration, it goes into reset, despite the fact that this does not happen when I use the design without the global clock buffers.

What could be causing this? How can I avoid it?

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Kenny_Tan
Moderator
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Usually, we use those signal in the Global as clock or reset. Can you try to move back your signal to local back? if you found that you have too many fan out on your signal, you can just limit it so that quartus will automatically duplicate those register accordingly.

 

What Quartus version and device that you were using? We have make some improvement on Qpro version for duplicate register in assignment editor.

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DMAHM1
Beginner
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Moving the signal back to local fixes the issue.

How big is the fanout supported by the global clock buffers?

I'm using Quartus Standard Edition 19.1 with the DE1-SoC board.

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Kenny_Tan
Moderator
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How big is the fanout supported by the global clock buffers?

It would be unlimited

 

The problem is that, if you put your signal to global clock buffers, they might not have any more relationship between your data and clock signal. Since both your clock and data signal are in global clock buffers.

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DMAHM1
Beginner
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The specific part of the design where I'm using this signal is combinational, so there shouldn't be a relationship between the data and the clock signal.

However, my main problem is that using the global clock buffers for this signal causes the board to go into reset. Is there another recommendation for routing a signal to many nodes in a way that efficiently utilizes the available routing resources?

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Kenny_Tan
Moderator
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How much fan out that you are looking into? Can you send us the screenshot of the report file showing that?

 

Also, usually, high fan out happened on the register, can you add additional register before the combi to have the high fan out?

 

Is there another recommendation for routing a signal to many nodes in a way that efficiently utilizes the available routing resources?

What I would suggest is used design partition, this way, you can preserve the routing and it will not cause other logic to interfere with your high fan out combi.

 

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DMAHM1
Beginner
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I'm looking into connecting the signal to thousands of LUTs.

I think the fanout was the issue since the other solutions you suggested stopped the board from going into reset.

Thank you for the design partition suggestion, that was also helpful.

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Kenny_Tan
Moderator
876 Views

Good to hear that design partition was helpful. Let us know if this solution is sufficient?

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Kenny_Tan
Moderator
876 Views

Any update?

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DMAHM1
Beginner
876 Views

The design partition solution is sufficient for my purposes. Thank you

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