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tflekan_ddc
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Registered: ‎03-01-2021

Vivado simulator cpu time

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I've been running simulations to compare the simulation speeds of Vivado and ModelSim.  When I run the Vivado simulation, it takes significantly longer to complete the same simulation, 5.5 hours for Vivado vs 4 hours for ModelSim.  This simulation is strictly VHDL and has no Xilinx IP.
 
Looking at the TCL log in Vivado, I notice that the elapsed time reported is much longer than the cpu time.  I ran this on a Windows desktop overnight and had nothing else running the background.

Note: Simulation ended
Time: 735451825 ns Iteration: 2 Process: /b1553_tb/sim_stop File: C:/Xilinx_Projects/simulation_comparison/modelsim/1553/tb/b1553_tb.vhd
Failure: This is not a failure
Time: 735451825 ns Iteration: 2 Process: /b1553_tb/sim_stop File: C:/Xilinx_Projects/simulation_comparison/modelsim/1553/tb/b1553_tb.vhd
$finish called at time : 735451825 ns : File "C:/Xilinx_Projects/simulation_comparison/modelsim/1553/tb/b1553_tb.vhd" Line 7656
run: Time (s): cpu = 00:28:22 ; elapsed = 05:42:19 . Memory (MB): peak = 1015.250 ; gain = 0.000
# set finish [clock seconds]
# puts "***Time for Vivado Simulation***"
***Time for Vivado Simulation***
# puts [expr {$finish - $start}]
20540
# puts "seconds"
seconds

Is there an explanation for why the elapsed time is so much greater than the cpu time?

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dpaul24
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Registered: ‎08-07-2014

@tflekan_ddc ,

That is expected.

xsim is free whereas you are paying for a Modelsim license.

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dpaul24
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Registered: ‎08-07-2014

@tflekan_ddc ,

That is expected.

xsim is free whereas you are paying for a Modelsim license.

------------FPGA enthusiast------------
Consider giving "Kudos" if you like my answer. Please mark my post "Accept as solution" if my answer has solved your problem
Asking for solutions to problems via PM will be ignored.

View solution in original post

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tflekan_ddc
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Registered: ‎03-01-2021

Thanks.  I understand that xsim is a free simulator and can't compete with ModelSim.  I would like to know why there is such a difference between elapsed and cpu time.  Is there something slowing down xsim?  What can slow down xsim so much?  Too many signals being logged?

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