Spartan3A : timing Constraints / DCM Outputs

Jul 09, 2007 3 Replies

Hi Folks,



have the following problem and couldn't found out yet how to solve it:



I have a clock input CLK_A and a DCM. I use CLKO and CLKFX outputs of DCM. CLKFX is configured for 4X CLK_A.



I define period constraint on CLK_A input port. And I see this constraint will be translated to both outputs CLK0 and CLKFX respectively. But timing analyzer does not analyze CLKFX output and its fanout logic. It just shows something like: " 0 items analyzed, 0 timing errors". I thought it should be enough to specify input clock frequency with TNM_NET and so on like:



NET "CLK_A" TNM_NET = "CLK_A"; TIMESPEC "TS_CLK_A" = PERIOD "TN_CLK_A" xx ns;



Any hint is appreciated.



Thanx Metin


And the solution was ...?

I replaced BUFGMUX with BUFG....than it started to analyze fanout logic timing. BUFGMUX was configured correct that desired clock went thru & arrived registers(verified with fpgaedit).

Strange...

Anybody any idea?

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