How the BUFG_GT providing output 1M when input as 125M ? Is it possible ?

[ssampath]

HI Friends,

How the BUFG_GT providing output 1M when input as 125M ? Is it possible ?

These clock period's are got from the TCL console ?

What am seeing is correct ? or is really BUFG_GT has capable to divide the input 125M clk to 1M clk ?

Any help or suggestions are highly appreciated.

-Sampath

[drjohnsmith]

get_property

https://www.xilinx.com/support/documentation/sw_manuals/xilinx2017_1/ug835-vivado-tcl-commands.pdf

What do you think its returning ?

[ssampath]

HI @drjohnsmith ,

Returing Time period. Is it not ?

-Sampath

[drjohnsmith]

Me thinks its the time period specified

I.e. its the period the tools have been asked to better in synthesis, NOT the best time they can achieve,

I have thought you might have over specified the timing constraints,
as an experiment, take off all your constraints, and see what that period command gives you

[ssampath]

Thank You @drjohnsmith ,

what i posted here is Before constrainting only ? The 125M is coming as expected, but why 1M coming out is confusion ?

-Sampath

[drjohnsmith]

If my understanding is correct, You have no constraints yet your asking the tools what constraints you have !

May be this is coming from any IP, and being back / forward propagated,

Suggests you constrain you design.
To be honest i cant remember last using get period, and Im hoping to learn on this as well.

[eschidl · Accepted solution]

Hi @ssampath,

physically the BUFG_GT cannot divide the clock this way. This is just created clock for timing.

To see where this constraint is set you could write out all constraints to a file (write_xdc <filename>). In the file you will find all constraints set and also in which file they are defined. This will narrow down where this is coming from.