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Clock Gating: Pre or Post Control

moogyd

Hi,

I am currently using lp_clock_gating_control_point set to postcontrol, simply because this was set in the the scripts I inherited.

 Are there any signficant advantages of postcontrol over precontrol?

I guess that postcontrol has a slight timing advantage, since precontrol has an additonal gate in the EN-D path.

Anything else? Which option do other users prefer or use?

Thanks,

 Steven

 

  •  Hi Steven,

    timing is certainly a difference but I believe the biggest difference is observabiliy for DFT coverage purposes. Post control limits your ability to check proper operation of the CG latch if not mistaken

    gh-

  • I suggest you check your target standard cell library to determine what kind of clock gating cells are available.  In many cases only one type is available.  For example:

    $ grep clock_gating slow.lib
      clock_gating_integrated_cell : "latch_posedge";
      clock_gating_integrated_cell : "latch_posedge";
      clock_gating_integrated_cell : "latch_posedge_precontrol";
      clock_gating_integrated_cell : "latch_posedge_precontrol";

     In this case, you would want to use precontrol.  If you chose post-control RC would be forced to build the clock gating cell from primitive components, which is obviously not what you would want.

    Brad

     

  • Hi,

    Brad, the library I am using contains both pre and post control integrated cells, so this is not an issue I need to consider.

    Grasshopper, I am not sure I understand your comment. I guess you mean that we will catch failts on the D input of the latch?

    Thanks for the feedback,

    Steven

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