create_generated_clock question

Question

Hi all!

I have a 120MHz clock coming into my design. I use this clock on register (called CLK_60) to divide it by 2, to create a 60MHz clock.

I believe I have constrained things correctly, but I get a warning that CLK_60 was found without an associated clock assignment.

Here's what I have in my .sdc:

create_clock -name CLK_I_120 -period 8.33333 [get_ports CLK_I_120]

create_generated_clock -divide_by 2 -name CLK_60 -source [get_pins CLK_60|clk]

Can anyone tell me where I might be going wrong?

Thanks!

altera_forum · Answer

Hi Awann,

You do not tell which clock has to be used as the source for the generated clock. You may try this:

create_generated_clock -divide_by 2 -name CLK_60 -source [get_ports CLK_I_120] [get_pins CLK_60|clk]

Grtz,

Richard.

altera_forum · Answer

I realized I did not add the target to my.sdc file.

So I changed the line to: create_generated_clock -divide_by 2 -name CLK_60 -source [get_pins CLK_60|clk] CLK_60

That fixed things, and taught me that proper caffeine levels should be achieved before attempting to write constraint files.

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