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4,078 Views
Registered: ‎12-23-2016

how to use timing limitation?

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hello! 

i want to learn how can i use timing limitaion in vivado but i can't find tutorial about that!

for example i have a circuit with 3 part, i need 100ns delay between part 1 and 2 in my circuit! how can i set this delay in vivado?

is there any tutorial for my question?

 

with thanks and regards.

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Moderator
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Registered: ‎07-01-2015

Re: how to use timing limitation?

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Hi @mohsenajorloo,

 

There are 2 things here. Are you trying to add delay between two paths or override the setup and hold analysis using set_max_delay?

Please go through https://www.xilinx.com/support/documentation/sw_manuals/xilinx2016_3/ug945-vivado-using-constraints-tutorial.pdf and https://www.xilinx.com/support/documentation/sw_manuals/xilinx2016_3/ug903-vivado-using-constraints.pdf for timing constraints. 

Thanks,
Arpan
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Moderator
Moderator
7,698 Views
Registered: ‎07-01-2015

Re: how to use timing limitation?

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Hi @mohsenajorloo,

 

There are 2 things here. Are you trying to add delay between two paths or override the setup and hold analysis using set_max_delay?

Please go through https://www.xilinx.com/support/documentation/sw_manuals/xilinx2016_3/ug945-vivado-using-constraints-tutorial.pdf and https://www.xilinx.com/support/documentation/sw_manuals/xilinx2016_3/ug903-vivado-using-constraints.pdf for timing constraints. 

Thanks,
Arpan
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Give Kudos to a post which you think is helpful and reply oriented.
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Guide
Guide
4,049 Views
Registered: ‎01-23-2009

Re: how to use timing limitation?

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If you are thinking of trying to use timing constraints to create a 100ns delay - don't....

 

First, 100ns is a VERY long delay for an FPGA - I doubt you could convince the router to add an intentional delay of that long.

 

Second, delays in a CMOS process (like the FPGA) vary significantly from part to part and over temperature and voltage. The "rule of thumb" variation is about 3:1, so if you want 100ns min, you will get almost 300ns max.

 

The way to manage time in an FPGA is through a clock. If you want certain things to happen 100ns apart, then make them synchronous (running on the same clock) and count off the correct number of clock cycles; i.e. 10 cycles of a 100MHz clock is 100ns.

 

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