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annotating switching activity

alexsieh

Dear fellows,

 Please shine some light in how I should annotate switching activity with TCF properly.

I used "dumptcf -internal" to create a tcf file from my testbench simulation. I did not set any scope, so the tcf file annotates all of the switching activites of my DUT and of my testbench. Thats ok rite? I am assuming the RTL Compiler will ignore the switching activity recorded from my testbench and use only the numbers regarding the DUT instances. After I read the tcf file in RC and synthesize my DUT, I noticed that in the power report, some negative numbers came out.

Question1. Why does Cadence allow negative dynamic power in its report? Does it make sense?

Then, I generated tcf files using "dumptcf -internal -scope .." to each hierachical instance of my DUT. In RC, I performed multiple commands "read_tcf ...", but the numbers do not add to what the non-scoped tcf file first gave me. The power analysis came out to be much lower even though I read the tcf files of each DUT instance.

Question2. Can i have RTL Compiler make multiple tcf reads? Does it override the previous read tcf?

Hope yall can help me! Sincerely,

Alex

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  • johannes

    Hi Alex,

    1. I never saw negative numbers in a power report before. Do you have any special IPs with customized lib-files in your design? Any other "special" library? I would try to do more analysis on the parts, where you see the negative numbers. I would even go down to cell level, and try to re-calculate what exactly happens (net capacitance, pin capacitance etc.). Do you get 100% TCF coverage on the sequential outputs after reading the TCF?

    2. Yes, you can use several read_tcf. It will overwrite only the toggles, which are redefined, and keep the others. You can also use "read_tcf -update", which will then combine the TCFs (i.e. not overwrite anything), where you can even give different weights using "-weight". I assume, you are using the "-instance" switch, in order to determine the scope, right? Also here: Do you get 100% TCF coverage?

    Regards,
    Johannes

     

Reply
  • johannes

    Hi Alex,

    1. I never saw negative numbers in a power report before. Do you have any special IPs with customized lib-files in your design? Any other "special" library? I would try to do more analysis on the parts, where you see the negative numbers. I would even go down to cell level, and try to re-calculate what exactly happens (net capacitance, pin capacitance etc.). Do you get 100% TCF coverage on the sequential outputs after reading the TCF?

    2. Yes, you can use several read_tcf. It will overwrite only the toggles, which are redefined, and keep the others. You can also use "read_tcf -update", which will then combine the TCFs (i.e. not overwrite anything), where you can even give different weights using "-weight". I assume, you are using the "-instance" switch, in order to determine the scope, right? Also here: Do you get 100% TCF coverage?

    Regards,
    Johannes

     

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