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AR# 41339

13.1 ISIM - Possible zero delay oscillation detected where simulation can not advance in time

Description

I am receiving the following Error when running ISIM:

ERROR: at 585 ns(10000): Iteration limit 10000 is reached. Possible zero delay oscillation detected where simulation can not advance in time because signals can not resolve to a stable value in File "..." Line x.
Please correct this code in order to advance past the current simulation time.

How can I debug this error?

Solution

You can use the "isim ptrace" command.  


This command, when enabled, will assert to the transcript window the specific process ISim is currently working on.  


Once you reach the iteration limit, check the last "visited" process.  


This will help to indicate which process is causing the problem.

 

You can enable ptrace by typing "isim ptrace on" in the ISim Tcl console. 

 

For more information, check out the "isim ptrace Overview and Syntax" section in ISE Help (http://www.xilinx.com/itp/xilinx10/isehelp/isehelp_start.htm)

 

*Most* of the time, iteration limits occur due to unlimited for loops in the testbench.  


Review for loops and wait statements in your testbench.

AR# 41339
Date Created 03/21/2011
Last Updated 10/01/2014
Status Active
Type General Article
Tools
  • ISE Design Suite - 13.1