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Charlycop
Observer
Observer
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Registered: ‎11-28-2020

36W and 125°C, what's wrong ?

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Hi,

After improving the parallelism in my design, the power estimation is way to high. 

What to look for, and what to change ?

bilan_power.jpgimpl_brams.jpg

I'm using vivado 2018.3 on Windows 10 pro 20H2 with a surface pro 4, i7 CPU and 16Go or RAM.
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Charlycop
Observer
Observer
463 Views
Registered: ‎11-28-2020

@olupj : the is a zynq7020, at 100MHz. it is a neural network accelerator.
@drjohnsmith  : it synthetise in few minuts, and the simulation even after synthesis is great.

HI, thank you all for your answers !

I was mistaken, and it is 2 problems completely different.

  1. the bitstream problem was about the constraint file missing.... (shame on me)
  2. the heat problem is just an estimation, and actually, it works fine in the card...

Thanks for your help !

 

I'm using vivado 2018.3 on Windows 10 pro 20H2 with a surface pro 4, i7 CPU and 16Go or RAM.

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11 Replies
drjohnsmith
Teacher
Teacher
680 Views
Registered: ‎07-09-2009

Power estimator is just what it says on the package, an estimation

     the better the information you put in the more accurate the answer can be.

Notice the confidence level is LOW.

Have you compared your numbers to a real system , or is this still at estimate stage ?

You have not said the chip, but 36 watts is well possible for the bigger chips if the DSP is running full out.

If you want it to run cooler,  and these numbers are true, then you need a heat sink 

 

   

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
joancab
Advisor
Advisor
671 Views
Registered: ‎05-11-2015

Well, you have an improved design plus a heater. Good for the winter days. Time to try one of those heatsinks with sodium that melts inside. 36W is a lot, but not anything unsurmountable. As @drjohnsmith says, it's an estimation. Real figure could be 25W or less if that helps... I don't know how that 'estimator' works but my common sense would expect it to maximize power for you to be in the safe side (although I know of some who think like that and purposely reduce the estimated power...)

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Charlycop
Observer
Observer
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Registered: ‎11-28-2020

The problem is that the synthesis and the impletation is very quick but bitstream doesn't want to be produced... do you think it is related ?

I'm using vivado 2018.3 on Windows 10 pro 20H2 with a surface pro 4, i7 CPU and 16Go or RAM.
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joancab
Advisor
Advisor
652 Views
Registered: ‎05-11-2015

"bitstream doesn't want to be produced" - well, that's a problem.

Implementation itself can take a long while but making the bitstream from the implemented design is quick (1-2 mins) and I would say independent from size and complexity.

That a bigger design takes longer to implement and will use more power is a loose generalization. There can be large low frequency designs running on low power and at the other end compact "monsters" draining amps and amps. 

bruce_karaffa
Scholar
Scholar
649 Views
Registered: ‎06-21-2017

Do you get an error message or does Generate Bitstream just keep spinning forever?

drjohnsmith
Teacher
Teacher
526 Views
Registered: ‎07-09-2009

Absolutely no link between power and bit stream not being produced. 

 

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
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drjohnsmith
Teacher
Teacher
524 Views
Registered: ‎07-09-2009

So new topic then,

How far does the build get ?

Have you simulated ? does that work ?

When you synthesis , do you get any errors / what are the warnings ?

 Assuming above works, when you implement, what are the errors reported ?

 

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
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olupj
Explorer
Explorer
514 Views
Registered: ‎01-27-2008

@Charlycop 

Did you "launch the power constraint advisor". There might be some design optimizations that can lower your power - but probably not 80% lower.

It looks like your device wants to support a 6W design (per thermal margin) not 36W.

You can get a much lower (well, half or a bit more)  theta-JA by adding a fan. However, I am not sure exactly how to add that, but it's covered in UG 907

Your design might be unsupported in the package - not sure what you're using but my current design has theta JA = 0.8 C/W. So you can move a lot more heat with better packaging.

It's not an easy problem.

Good luck,

Jerry

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olupj
Explorer
Explorer
509 Views
Registered: ‎01-27-2008

@Charlycop 

Re: setting operating "what if" scenarios".

So I took a quick look. When you run a power report, there's a popup UI that allows you to run with different scenarios, including changing thetaJA (to say, given a certain airflow, heatsink size, ambient temp, switching activity, etc... what do I need to dissipate that power).

You can run what if's with that - combined with the power constraint advisor you might at least get some idea of what's wrong.

So looking at the implemented design - it doesn't look too terrible. I am using 336 DSP48s in a design at 550 MHz and burning 0.279 W. Not sure how you can even get to 17W for DSP alone in your design.

What's your utilization? What's your clock rate?

 

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Charlycop
Observer
Observer
464 Views
Registered: ‎11-28-2020

@olupj : the is a zynq7020, at 100MHz. it is a neural network accelerator.
@drjohnsmith  : it synthetise in few minuts, and the simulation even after synthesis is great.

HI, thank you all for your answers !

I was mistaken, and it is 2 problems completely different.

  1. the bitstream problem was about the constraint file missing.... (shame on me)
  2. the heat problem is just an estimation, and actually, it works fine in the card...

Thanks for your help !

 

I'm using vivado 2018.3 on Windows 10 pro 20H2 with a surface pro 4, i7 CPU and 16Go or RAM.

View solution in original post

joancab
Advisor
Advisor
458 Views
Registered: ‎05-11-2015

To use 36W I expected a large device, like a zu7 or larger, but no way for a zynq7020 with 100 MHz. 

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