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Old 04-10-2006, 02:42 PM
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Default Re: xilinx DCM Timing warning

[email protected] wrote:
> Hi
> Iam trying to synthesize using syn. pro and P&R using ISE. Iam planning
> to use XIlinx-DCM and generate 66MHz (at which my design works) from
> 100MHz(osc. freq in board). Now in I gave autoconstrain
> frequency option. The top entity does have clk and inside the code DCM
> generates clkgen0_xc2v_v_Clk0B. The mul. and div. factor I gave is 2&3.
> It means my clk(100MHz) is multiplied by 2 and div. by 3 in DCM and I
> will get 66.66MHz. So in the ucf file I gave for clk 100MHz. While I
> translate my design in ISE, I get an warning like this.
> Checking timing specifications ...
> WARNING:XdmHelpers:681 - UCF definition of specification "TS_clk"
> overrides the
> definition found in the netlist or NCF file:
> UCF: PERIOD "clk" 10000.000000 pS HIGH 50.000000 %
> netlist/NCF: PERIOD:clk:4159.000000S:HIGH:50.000000%
> INFO:XdmHelpers:851 - TNM "clk", used in period specification "TS_clk",
> was
> traced into DCM instance "clkgen0/xc2v.v/dll0". The following new
> TNM groups
> and period specifications were generated at the DCM output(s):
> CLKFX: TS_clkgen0_xc2v_v_Clk0B=PERIOD clkgen0_xc2v_v_Clk0B
> TS_clk/0.666667
> HIGH 50.000000%
> WARNING:XdmHelpers:662 - Period specification "TS_clkgen0_xc2v_v_Clk0B"
> references the TNM group "clkgen0_xc2v_v_Clk0B", which contains both
> pads and
> synchronous elements. The timing analyzer will ignore the pads for
> this
> specification. You might want to use a qualifier (e.g. "FFS") on the
> property to remove the pads from this group.
> Checking expanded design ...
> Why in the generated clock I see TS_clk/0.666667 instead of TS_CLK/1.5
> which makes gen. clock to be 66.666MHz.
> Any help is appreciated,
> Prakash

It looks like the time spec is a period rather than a frequency, so it
be multiplied by 1.5, not divided by 1.5 going from 100 to 66.667 MHz.
period goes from 10.0ns to 15.0ns

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