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Adventurer
Adventurer
506 Views
Registered: ‎05-09-2018

Synthesis does not correctly interpret timed based constants

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In the old ISE tools, I was able to define time based constants and have synthesis interpret them correctly. Vivado does not interpret them and sets them to zero. For example:

 

constant clock_period : time := 10 ns;

constant cycle_period : time := 100 us;

constant clocks_per_cycle : integer := cycle_period/clock_period;

 

Is there a particular library needed by Vivado to properly interpret time based constants?

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Scholar jmcclusk
Scholar
554 Views
Registered: ‎02-24-2014

Re: Synthesis does not correctly interpret timed based constants

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This is a known issue with Vivado synthesis.  It usually makes an error when doing division on type TIME.    The workaround is to use type REAL, which is IEEE double precision.   This may require more documentation in the comments to make the units and scale more obvious, but the arithmetic is always correct.

Don't forget to close a thread when possible by accepting a post as a solution.

View solution in original post

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Scholar jmcclusk
Scholar
555 Views
Registered: ‎02-24-2014

Re: Synthesis does not correctly interpret timed based constants

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This is a known issue with Vivado synthesis.  It usually makes an error when doing division on type TIME.    The workaround is to use type REAL, which is IEEE double precision.   This may require more documentation in the comments to make the units and scale more obvious, but the arithmetic is always correct.

Don't forget to close a thread when possible by accepting a post as a solution.

View solution in original post

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Adventurer
Adventurer
487 Views
Registered: ‎05-09-2018

Re: Synthesis does not correctly interpret timed based constants

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Thanks!
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