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12498 Discussions

How to manage multiple clocks in the same bank that each require their own PLL?


I'm working on a Cyclone V GX9 device and I have two input clocks in the same bank. One of these clocks is used by the Nios and a PLL is required for SDRAM clocking. The other clock is referenced to serial data and requires it own, separate PLL.


By default, the fitter maps FRACTIONALPLL_X121_Y1_N0 to the SDRAM PLL, this leaves the other clock generating the following error.

Error (177020): The PLL reference clock was not placed in a dedicated input pin that can reach the fractional PLL


I have tried forcing the clocks to other PLLs with the SET_LOCATION command. Unsurprisingly, I get the same error.


Unfortunately, I'm not in a position where I can change the pin locations of the clocks. Any advice on how to successfully get this signals out to another PLL?

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2 Replies



As I understand it, you are observing some Fitter issues when tyring to use fPLL for your XCVR. By merely looking at the error message, it seems to indicate that the refclk pin for the fPLL which drive the XCVR is not assigned to a dedicated XCVR refclk input pin. Would you mind to check if the fPLL refclk is placed to dedicated XCVR refclk pin?


If you have placed the refclk to dedicated XCVR refclk pin and still observe issue, would you mind to share with me a simple test design with only the XCVR instances which could replicate the observation? This would be helpful for me to further look into it.


Please let me know if there is any concern. Thank you.


Best regards,

Chee Pin





Just would like to follow up with you on this. Thank you.