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Beginner
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set_clock_group constraints question!! plz help..

I have clocks, one of which is a ripple clock. I don't know how to set_clock_group this. 

Details are shown in the picture.

 

If you look at the picture, there are a_clock and b,c,d,e. a_clock is the clock that comes into a input port, and b is the half-rate ripple clock made from a_clock. And c_clock is also input clock, a_clock and c_clock are completely asynchronous clock.

I muxed the a and b clock and specified d and e_clock respectively using create_generate_clock.

 

i'm about to set_clock_group them all. As far as I know, d and e have to use -exclusive, but the problem is that a,b,d,e are all related clocks, which are confusing.

 

Tell me how to modify the set_clock_group in the picture.

Thank you so much.

 

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Valued Contributor II
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You could use something like this:

 

set_time_format -unit ns -decimal_places 3 # Create the first input clock to the mux create_clock -period 10 -name clockA [get_ports a_clock] # Create the second input clock to the mux create_clock -period 10 -name clockB [get_ports b_clock] #Cut transfers between FirstClock and SecondClock set_clock_groups -exclusive -group {clockA} -group {clockB}

or the following for externally switched clocks

 

set_time_format -unit ns -decimal_places 3 # Create the first input clock on the clock port create_clock -period 10 -name clockA [get_ports a_clock] # Create the second input clock on the same clock port create_clock -period 10 -name clockB [get_ports b_clock] -add # Cut transfers between FirstClock and SecondClock set_clock_groups -exclusive -group { clockA } -group { clockB }

 

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Highlighted
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Hi,

 

You can use set_clock_groups with either [-asynchronous] or [-exclusive]. Asynchronous clocks (-asynchronous) are completely unrelated: they have different ideal clock sources. Exclusive clocks (-exclusive) are not active at the same time, such as multiplexed clocks. 

 

Thanks.

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