Feedback return path used by PLL(s) in location FRACTIONALPLL_X68_Y54_N0 is not of the recommended type

[Lilian_61]

I am using Cyclone V 5CGXFC FPGA. And there is 25MHz clock input. I used the 25MHz clock source to generate other frequency clock for platform usage. But when I use PLL, I got the below warning. I don't know how to resolve it.

Warning (12392): Feedback return path used by PLL(s) in location FRACTIONALPLL_X68_Y54_N0 is not of the recommended type

Info (177008): PLL pll_25MHz_cv:pll_25MHz_cv_inst|pll_25MHz_cv_0002:pll_25mhz_cv_inst|altera_pll:altera_pll_i|general[0].gpll~FRACTIONAL_PLL

[SreekumarR_G_Intel]

Can I know what is the mode of the PLL used in the design ?

(ie Normal mode ; Zero Delay Buffer mode or No Compensation mode )

Would it possible to share the your setting and pin used for Inclk0 ?

Thank you,

Regards,

Sree

[Lilian_61]

The PLL used is Normal Mode.

Below is physical connection. The CLK25M_TXCO_FPGA1_AC_P/N is differential clock generated by TCXO.

In FPGA setting, the IO standard is set as DIFFERENTIAL LVPECL, and the CLK25M_TCXO_FPGA1_AC_P is the refclk of PLL module.

[SreekumarR_G_Intel]

I created the small example design with Fractional PLL and the IO standrad specified . When I complie ,i got warning given below and which can be overiddern using below KDB link.

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

https://www.intel.com/content/www/us/en/programmable/support/support-resources/knowledge-base/solutions/rd10232014_332.html?wapkw=Warning%20%28177007%29:

can you check the deign I attcahed and re-create the warning and post it back. This will help me analyze the further.

Thank you,

Regards,

Sree

[Lilian_61]

Thanks for your help.

I re-compile your project, and I don't find the same warning in report.

The reason I want to resolve this warning, because there are timing analysis issue, and I think this warning have an effect.

I also post part of the other warnings here, may it can offer some help. I tried to fix it myself, but I failed.

The pll_clk50m, pll_clk25m, pll_clk62m5 and pll_clk20m are generated by PLL module.

---------------------------------------------------------------------------------------------------------------------------------

Warning (16305): Feedback path used by PLL(s) in location FRACTIONALPLL_X68_Y54_N0 was routed for regional clock compensation but the clock targeted for compensation was routed as a global clock

Warning (332174): Ignored filter at mi.sdc(37): pll_clk50m could not be matched with a port or pin or register or keeper or net or combinational node or node

Warning (332174): Ignored filter at mi.sdc(38): pll_clk25m could not be matched with a port or pin or register or keeper or net or combinational node or node

Warning (332174): Ignored filter at mi.sdc(39): pll_clk62m5 could not be matched with a port or pin or register or keeper or net or combinational node or node

Warning (332174): Ignored filter at mi.sdc(40): pll_clk20m could not be matched with a port or pin or register or keeper or net or combinational node or node

Warning (332174): Ignored filter at mi.sdc(66): CLK50M_PLL could not be matched with a clock

Warning (332049): Ignored set_clock_groups at mi.sdc(66): Argument -group with value CLK50M_PLL could not match any element of the following types: ( clk )

Info (332050): set_clock_groups -exclusive -group {CLK50M_PLL}

Warning (332174): Ignored filter at mi.sdc(67): CLK25M_PLL could not be matched with a clock

Warning (332049): Ignored set_clock_groups at mi.sdc(67): Argument -group with value CLK25M_PLL could not match any element of the following types: ( clk )

Info (332050): set_clock_groups -exclusive -group {CLK25M_PLL}

Warning (332174): Ignored filter at mi.sdc(68): CLK62M5_PLL could not be matched with a clock

Warning (332049): Ignored set_clock_groups at mi.sdc(68): Argument -group with value CLK62M5_PLL could not match any element of the following types: ( clk )

Info (332050): set_clock_groups -exclusive -group {CLK62M5_PLL}

Warning (332174): Ignored filter at mi.sdc(69): CLK20M_PLL could not be matched with a clock

Warning (332049): Ignored set_clock_groups at mi.sdc(69): Argument -group with value CLK20M_PLL could not match any element of the following types: ( clk )

Info (332050): set_clock_groups -exclusive -group {CLK20M_PLL}

Warning (332049): Ignored set_false_path at mi.sdc(79): Argument <from> is an empty collection

Info (332050): set_false_path -from [get_clocks CLK62M5_PLL] -to [get_clocks CLK62M5_SYS]

Warning (332049): Ignored set_false_path at mi.sdc(80): Argument <to> is an empty collection

Info (332050): set_false_path -from [get_clocks CLK62M5_SYS] -to [get_clocks CLK62M5_PLL]

---------------------------------------------------------------------------------------------------------------------------------

[SreekumarR_G_Intel]

Would it possible to provide the design files via email or IPS case ?

Thank you,

Regards,

Sree

[SreekumarR_G_Intel]

one more thought, would it possible to change the pin allocation and try , Speically to Regional clk pins ?

Thank you,

Regards,

Sree

[SreekumarR_G_Intel]

Can i know update on this issue ?

Thank you ,

Regards,

Sree