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Beginner
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"Match PLL Compensation Clock" assignment doesn't work

Hi,

When I used Quartus to compile for a cyclone V device I got an warning, which was just the one in the link below. I followed the Workaround/Fix part of the link to try to remove the warning but failed:

https://www.intel.com/content/www/us/en/programmable/support/support-resources/knowledge-base/soluti...

There are some information about the PLL for the project:

  1. There is only one PLL instance in the project, the type is integer PLL and normal mode with automatic reset;
  2. When I generated PLL I didn't see the options for compensation;
  3. When I set the "Match PLL Compensation Clock" assignment, I chose the node that could have a green tick ahead the assignment, which was end with altera_pll:altera_pll_i|general[0].gpll.

 

My questions are:

  1. Whether the PLL clocks are not compensated if the warning is there?
  2. What can I do to eliminate the warning?

 

Thank you.

 

Best regards,

Ross

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11 Replies
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New Contributor II
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Hi RLee42!

 

First of all, there are different compensation modes in Altera PLL IP core, so it's strange that you didn't see them. You can read about them here : https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/ug/altera_pll.pdf - Operation modes.

You can choose them from the GUI - you already made a selection (normal).

 

About your questions -

  1. In that case fitter will compensate all PLL clocks like this : " Normal mode—the PLL feedback path source is a global or regional clock network, minimizing clock delay from the input clock pin to the core registers through global or regional clock network."
  2. The workaround should help - I successfully eliminated problem in my own project.

 

Hope that helps.

 

--

Best Regards,

Ivan

 

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Employee
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Yes, you should be able to see each of compensation in PLL IP GUI. Just select any of them and see if it will get rid of the warning.

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Employee
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Please use this command in qsf to set which clock output to be compensated => set_instance_assignment -name MATCH_PLL_COMPENSATION_CLOCK ON -to "<PLL name>|outclk_wire[0]"
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Beginner
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Hi lvan,

Thank you for your time.

I did choose "normal" when I generated PLL and I thought Quartus should know the way to compensate, however, I still got a warning as below:

Warning (177007): PLL(s) placed in location FRACTIONALPLL_X0_Y1_N0 do not have a PLL clock to compensate specified - the Fitter will attempt to compensate all PLL clocks.

Then I assumed that there might be some extra options for compensation which I missed. That's why I said "When I generated PLL I didn't see the options for compensation".

Thank you.​

 

Best Regards,

Ross

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New Contributor II
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Hi RLee42!

 

Ok, I see.

 

I can say that in most cases you can ignore that warning, but to eliminate it, try what GNg suggests below -> => set_instance_assignment -name MATCH_PLL_COMPENSATION_CLOCK ON -to "<PLL name>|outclk_wire[0]"

 

--

Best Regards,

Ivan

 

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Beginner
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Hi GNg,

Thank you for your reply.

As Even I chose "Normal mode" when generated the PLL, I still got a warning as below:

Warning (177007): PLL(s) placed in location FRACTIONALPLL_X0_Y1_N0 do not have a PLL clock to compensate specified - the Fitter will attempt to compensate all PLL clocks

Then I also tried adding a command in qsf by using assignment editor.

I tried two commands separately which could have a green tick in assignment editor as below (my PLL didn't have outclk_wire[0], which was generated by Quartus Lite 18.1 for cyclone V):

set_instance_assignment -name MATCH_PLL_COMPENSATION_CLOCK ON -to "pll:u_pll|pll_0002:pll_inst|altera_pll:altera_pll_i|general[0].gpll"

set_instance_assignment -name MATCH_PLL_COMPENSATION_CLOCK ON -to "pll:u_pll|pll_0002:pll_inst|altera_pll:altera_pll_i|general[0].gpll~FRACTIONAL_PLL"

The first one was generated by choosing a node in assignment editor.

The second one was copied and pasted into the assignment editor from the info that in Warning (177007).

However, I got another warning for this command:

Warning (171167): Found invalid Fitter assignments. See the Ignored Assignments panel in the Fitter Compilation Report for more information.

So, this command didn't work, though I thought the clock output was correct.

Thank you.

Best regards,

Ross

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Employee
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I extracted the command from my PLL design built in Quartus version 18.1. You should see the clock name "~outclk_wire[0]". set_instance_assignment -name MATCH_PLL_COMPENSATION_CLOCK ON -to "pll_150out:pll_150out_inst|pll_150out_0002:pll_150out_inst|altera_pll:altera_pll_i|outclk_wire[0]" Another way to find its clock output name is from Fitter report. Go to Fitter>Resource section>Global & other fast signals> find that corresponding PLL's signal suffix with "outclk_wire"
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Beginner
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Hi lvan,

Thank you and I tried it too but failed.

I'm not sure if you can see the message I replied GNg.

Yes, you are right that I could ignore it. I just have interest on why the warning is there that I may have something that can be improved.

I don't know whether it matters that I couldn't edit the PLL IP in the project.

It was also strange that I generated the PLL in Quartus Lite 18.1 and tried editing it in Quartus Lite 18.1 too, which was also met by some other people .

I might try to ​generate it again if no better choice.

Thank you.

Best regards,

Ross

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New Contributor II
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Hi RLee42!

 

I can see the message of GNg, and first of all, please try to do what he suggests - you need to find from netlist "~outclk_wire[0]".

 

As about problems with editing of PLL in 18.1 Quartus it is another problem, you can explain the problem in more details.

 

--

Best Regards,

Ivan

 

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Beginner
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Hi GNg,

 

Thank you and I found it at last.

 

Best regards,

Ross

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Beginner
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Hi Ivan,

 

Thank you and I found it at last.

 

Best regards,

Ross

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