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

Altera_Forum
Honored Contributor II
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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
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Altera_Forum
Honored Contributor II
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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
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Altera_Forum
Honored Contributor II
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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.
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