How to manage user 'reset' for post-synthesis simulation

Aug 02, 2005 1 Replies
P

Dear



I need some comments on managing the 'global reset' in ISE6.3(XST) from experienced one.



I am post-placement-and-routing simulating in Modelsim. This module has input reset port. During synthesis/mapping, there is no warning/error.



During the simulation, followings are observed, which are maybe or maybe not be problematic.


- In behavioral simulation, it works, even though no value is assigned to reset signal in test vector.


- After placement-and-routing simulation, it works, only when we put reset signal is '0' in test vector.



I am wondering if this is problematic.



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G

I have found that when reset behaves differently in simulation than in PAR it usually points to the global reset path been gated. Generally you should treat reset signals with almost the same care you treat Clk signals (most importantly by not gating them).

Try also passing the reset signal through an BUF or even edge detecting it to ensure that it is stable. (remember that most reset signals come from outside pins and can have wild fluctuations before settling). Generally, behavioral simulations assume ideal signals.

Hope this helps.

Robin

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