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Altera_Forum's avatar
Altera_Forum
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10 years ago

dedicated input clock I/O pin as regular input in Cyclone IV

Hello,

I would like to use GLK3 dedicated input clock as regular user input on Cyclone IV EP4CE6E22

It seems OK but the fitter (Quartus 13.1) return the following warning:

Warning (176228): Can't pack node xxxx and I/O node xxxx -- I/O node is a dedicated I/O pin

Can I ignore this message safely?

Regards

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    Yes, you can use dedicated clock input pins for general purpose input (but not output) signals. Indeed you can also use general purpose I/O for clock inputs too but if you can avoid it I would.

    I don't think that warning is (necessarily) related to such an assignment. I've just tried this and don't see a similar warning.

    Do you have a clock going into a general purpose I/O pin? I think that is more likely to result in such a warning. Quartus may find it difficult to route a clock, coming in on an I/O pin, to a large number of registers.

    Cheers,

    Alex
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    The warning message concerns an IO input that is not used as a clock. When I have this message (regular input on GCLK pin) the fitter report indicates a fanout of 0.

    I have tried to remove the pin allocation and the message disappears. Moreover, in this case the fitter report indicates a fanout of 2...

    I don't use clock going into general purpose. All input clocks are located on GCLKx pins.