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  #1 (permalink)  
Old 04-22-2005, 09:39 PM
jason.stubbs
Guest
 
Posts: n/a
Default Virtex 4 Power consumption

Can anyone give me an estimate of the max current a V4fx60 FPGA will
draw for VCCINT @ 1.2v, & VCCAUX and VCCO @ 2.5v?

I am designing a board with 9 of them and need a rough idea of power
required.

Any help would be appreciated.

Jason

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  #2 (permalink)  
Old 04-22-2005, 09:52 PM
Amora
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Using the Xilinx XPower tool, you can get an estimate of the worst case
power consumption. If you just crank in 1.2v for VCCINT and 2.5v for
VCCO, then by a simple division, you could get the max current drawn by
a V4FX60 FPGA for a specific design. Different designs will draw
different amounts of current.

Amr

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  #3 (permalink)  
Old 04-25-2005, 01:53 PM
jason.stubbs
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Posts: n/a
Default Re: Virtex 4 Power consumption

XPower says I need a completely mapped NCD file to get started. I dont
have anything from the FPGA designer that I can use yet.

Can I do anything without requiring the NCD file?

Jason

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  #4 (permalink)  
Old 04-25-2005, 06:21 PM
Austin Lesea
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Posts: n/a
Default Re: Virtex 4 Power consumption

Jason,

Use the on line power estimator tool.

Less accurate, but it should allow you to get a good feeling for the
power needed for you design.

Austin

jason.stubbs wrote:

> XPower says I need a completely mapped NCD file to get started. I dont
> have anything from the FPGA designer that I can use yet.
>
> Can I do anything without requiring the NCD file?
>
> Jason
>

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  #5 (permalink)  
Old 04-25-2005, 07:27 PM
jason.stubbs
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Posts: n/a
Default Re: Virtex 4 Power consumption

Austin,

The online tool also requires details of the design that I dont have.
Can you guide me in what I have to enter to estimate the worse case?

Thanks

Jason

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  #6 (permalink)  
Old 04-25-2005, 09:50 PM
Austin Lesea
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Posts: n/a
Default Re: Virtex 4 Power consumption

Jason,

The 'worst case'? For a FPGA the 'worst case' is probably something you
don't even want to consider.

For example, if you put in all 100% of the CLB FF's toggling at 300 MHz,
you are likely to see that the power required is so large that you can
not heatsink the device (would melt the solder and fall off the pcb).

The power estimators need your case, not the 'worst case'.

Austin

jason.stubbs wrote:

> Austin,
>
> The online tool also requires details of the design that I dont have.
> Can you guide me in what I have to enter to estimate the worse case?
>
> Thanks
>
> Jason
>

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  #7 (permalink)  
Old 04-25-2005, 10:24 PM
Hal Murray
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption


>> The online tool also requires details of the design that I dont have.
>> Can you guide me in what I have to enter to estimate the worse case?


Make some estimates or guesses. That will at least give you a number.

Then go back and change the numbers you aren't sure about. If the
answer doesn't change much then don't worry much. If the answer
depends a lot on your wild guesses then you have learned
that you have to work on that part of the design so you will have
meaningful numbers to feed to the power-estimator.

--
The suespammers.org mail server is located in California. So are all my
other mailboxes. Please do not send unsolicited bulk e-mail or unsolicited
commercial e-mail to my suespammers.org address or any of my other addresses.
These are my opinions, not necessarily my employer's. I hate spam.

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  #8 (permalink)  
Old 04-26-2005, 12:42 PM
Brendan Cullen
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Hi Jason,

"jason.stubbs" wrote:

> Austin,
>
> The online tool also requires details of the design that I dont have.
> Can you guide me in what I have to enter to estimate the worse case?


In terms of "PVT" - Process, Voltage & Temperature : In the WPT currently
you can, for V4 FX devices, vary Vccint and the ambient temperature.
That partially addresses the "V" & "T".

On the "P" or process side here are a few guidelines :
- if you are at worst case process and worst case voltage (1.3 V) you
should use a factor of 2.5.
- if you are at worst case process but at nominal voltage you should use
a 2.0 factor.

Brendan


>
>
> Thanks
>
> Jason


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  #9 (permalink)  
Old 04-26-2005, 02:16 PM
Paul Leventis \(at home\)
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Hi Brendan,

> In terms of "PVT" - Process, Voltage & Temperature : In the WPT currently
> you can, for V4 FX devices, vary Vccint and the ambient temperature.


When I enter 1.25V vs. 1.20V in WPT 4.1, I'm given 687 mW vs. 660 mW of
VccInt static power for a LX80, in addition to the 234 mW of VccAux power.

Similarly, for some random amount of logic utlization, I get 2727 mW vs.
2618 mW of dynamic power.

It seems to me that all the tool is doing is increasing the V in P = VI.
However, increasing V should (a) increase dynamic current draw roughly
linearly and (b) increase sub-threshold leakage by the square of 1.25/1.2.
Neither of these effects appear to be modeled.

Regards,

Paul Leventis
Altera Corp.


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  #10 (permalink)  
Old 04-26-2005, 04:11 PM
Austin Lesea
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Paul,

Since we power the pass gates from Vccaux through a band gap referenced
supply for the entire interconnect, many simple minded formulas that you
may come up with will not apply.

Austin

Paul Leventis (at home) wrote:

> Hi Brendan,
>
>
>>In terms of "PVT" - Process, Voltage & Temperature : In the WPT currently
>>you can, for V4 FX devices, vary Vccint and the ambient temperature.

>
>
> When I enter 1.25V vs. 1.20V in WPT 4.1, I'm given 687 mW vs. 660 mW of
> VccInt static power for a LX80, in addition to the 234 mW of VccAux power.
>
> Similarly, for some random amount of logic utlization, I get 2727 mW vs.
> 2618 mW of dynamic power.
>
> It seems to me that all the tool is doing is increasing the V in P = VI.
> However, increasing V should (a) increase dynamic current draw roughly
> linearly and (b) increase sub-threshold leakage by the square of 1.25/1.2.
> Neither of these effects appear to be modeled.
>
> Regards,
>
> Paul Leventis
> Altera Corp.
>
>

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  #11 (permalink)  
Old 04-26-2005, 08:03 PM
Yaju N
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption


Austin Lesea wrote:
> Jason,
>
> The 'worst case'? For a FPGA the 'worst case' is probably something

you
> don't even want to consider.
>
> For example, if you put in all 100% of the CLB FF's toggling at 300

MHz,
> you are likely to see that the power required is so large that you

can
> not heatsink the device (would melt the solder and fall off the pcb).


WOW. Now I really want to try doing, and make the FPGA fall off the
PCB. That would be really cool.
In building my board, I have used 1A voltage regulators to be on the
safe side. I have designed my board to be flexible with various
designs.

I guess a question which Austin or other members could help answer
would be, what should be the best closest worst case when a relevant
design is implemented on the FPGA. Since right now, I cant think of any
design which could require all the CLBs toggling at such a high
frequency. So maybe a design with Microblaze and very intensive DSP
tasks implemented on the FPGA. What could be the power consumption for
that or some other more intensive design on an FPGA

The online tool does not really help if you are planning on getting the
best perfomance yeild off the FPGA, and need to know the power
constraints before hand.

-Yaju




> The power estimators need your case, not the 'worst case'.
>
> Austin
>
> jason.stubbs wrote:
>
> > Austin,
> >
> > The online tool also requires details of the design that I dont

have.
> > Can you guide me in what I have to enter to estimate the worse

case?
> >
> > Thanks
> >
> > Jason
> >


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  #12 (permalink)  
Old 04-26-2005, 09:38 PM
Peter Alfke
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

It's like asking what is the price of a car or a house or a meal or a
shirt or a book.
There is always a more than 10-to-1 range.

I think 1A is very stingy when you want to do fast DSP, where many
nodes wiggle very fast.
Try it out, and keep your options open.
A 1.5 or 1.2-V AA battery is a convenient voltage source for trying it
out. They give you >1A for an hour, enough time for some experiments.
Peter Alfke, Xilinx

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  #13 (permalink)  
Old 04-26-2005, 09:42 PM
Paul Leventis
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Hi Austin,

> Since we power the pass gates from Vccaux through a band gap

referenced
> supply for the entire interconnect, many simple minded formulas that

you
> may come up with will not apply.


Excuse my simple-mindedness, but I am having trouble understanding.
You have no circuitry powered off the actual VccInt rail? Your routing
buffers, LUTs, DSPs, RAMs and other hard-IP blocks do not use VccInt
but rather run off the regulated VccAux-driven supply?

Yes, I will concur that simple rules-of-thumb are never quite true in
practice, and depend on exact circuits used. But are you suggesting
that your supply current doesn't change with voltage? At all?

Paul Leventis
Altera Corp.

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  #14 (permalink)  
Old 04-26-2005, 11:31 PM
Austin Lesea
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Paul,

It does change (with V), as is shown by the predictor.

And yes, we do use Vccint. We also use Vccaux.

Nothing is ever as simple as it first seems.

The devil is in the details, and telling you how it works would just
allow you to copy it, and improve your own estimator.

Austin

Paul Leventis wrote:

> Hi Austin,
>
>
>>Since we power the pass gates from Vccaux through a band gap

>
> referenced
>
>>supply for the entire interconnect, many simple minded formulas that

>
> you
>
>>may come up with will not apply.

>
>
> Excuse my simple-mindedness, but I am having trouble understanding.
> You have no circuitry powered off the actual VccInt rail? Your routing
> buffers, LUTs, DSPs, RAMs and other hard-IP blocks do not use VccInt
> but rather run off the regulated VccAux-driven supply?
>
> Yes, I will concur that simple rules-of-thumb are never quite true in
> practice, and depend on exact circuits used. But are you suggesting
> that your supply current doesn't change with voltage? At all?
>
> Paul Leventis
> Altera Corp.
>

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  #15 (permalink)  
Old 04-27-2005, 05:23 AM
Hal Murray
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

>The online tool does not really help if you are planning on getting the
>best perfomance yeild off the FPGA, and need to know the power
>constraints before hand.


I think the problem is that the worst case is so nasty that it
isn't interesting.

Can you go backwards? How much power can you get rid of? How
big a heat sink and/or fan are you going to have?

There isn't much need for a power supply to put out more than that.
Maybe 2x or 10x if you want to run in short bursts.

Another approach is to look at several prototyping boards and see
what they have. If you don't hear complaints about it here that's
probably big enough.

You could also add some big connection points so at worst you
can add wires over to an external power supply.

--
The suespammers.org mail server is located in California. So are all my
other mailboxes. Please do not send unsolicited bulk e-mail or unsolicited
commercial e-mail to my suespammers.org address or any of my other addresses.
These are my opinions, not necessarily my employer's. I hate spam.

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  #16 (permalink)  
Old 04-28-2005, 12:00 AM
Ljubisa Bajic
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Hi Austin,

I also tried using the power estimation tool on Xilinx' web site and
ran into pretty much the same results as Paul described earlier in the
thread.
Specifically, I tried >10 different configurations with a V4 LX80
part; varying the following parameters (all "utilization" parameters
were between low and medium values, Vccint was varied between 1.1V and
1.3V):

Vccint
CLB Usage
FIFO Usage
RAM usage
DSP block usage
Amount of air flow

What I found is that for every "configuration" I tried the ratio of
Vccint_new/Vccint_old was almost exactly equal (equal at least to the
precision of a mW) to the ratio of Power_new/Power_old (where the
Vccint
values are between 1.1 and 1.3 and Power_{new,old} refers to only the
power
reported as dissipated on the Vccint rail.

Could you please shed some light on the behaviour described above? Are
Paul and I simply doing something completely wrong with the power
estimator?

In order to avoid coming off as simple minded, I will refrain from any
speculation on my side.

Thanks,
Ljubisa Bajic
ATI Technologies


Austin Lesea <[email protected]> wrote in message news:<[email protected]>...
> Paul,
>
> It does change (with V), as is shown by the predictor.
>
> And yes, we do use Vccint. We also use Vccaux.
>
> Nothing is ever as simple as it first seems.
>
> The devil is in the details, and telling you how it works would just
> allow you to copy it, and improve your own estimator.
>
> Austin
>
> Paul Leventis wrote:
>
> > Hi Austin,
> >
> >
> >>Since we power the pass gates from Vccaux through a band gap

> >
> > referenced
> >
> >>supply for the entire interconnect, many simple minded formulas that

> >
> > you
> >
> >>may come up with will not apply.

> >
> >
> > Excuse my simple-mindedness, but I am having trouble understanding.
> > You have no circuitry powered off the actual VccInt rail? Your routing
> > buffers, LUTs, DSPs, RAMs and other hard-IP blocks do not use VccInt
> > but rather run off the regulated VccAux-driven supply?
> >
> > Yes, I will concur that simple rules-of-thumb are never quite true in
> > practice, and depend on exact circuits used. But are you suggesting
> > that your supply current doesn't change with voltage? At all?
> >
> > Paul Leventis
> > Altera Corp.
> >

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  #17 (permalink)  
Old 04-29-2005, 06:36 PM
Ljubisa Bajic
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Hi Everyone,

Since, despite previously voicing opinions on the topic, Austin does not seem
to be willing/interested to reply to my question, I would like to extend it to
anyone at Xilinx, or in general anyone who might know the answer: Can anyone
explain the results that are described in my previous posting in this thread?

Thanks in advance,
Ljubisa Bajic
ATI Technologies


[email protected] (Ljubisa Bajic) wrote in message news:<[email protected] com>...
> Hi Austin,
>
> I also tried using the power estimation tool on Xilinx' web site and
> ran into pretty much the same results as Paul described earlier in the
> thread.
> Specifically, I tried >10 different configurations with a V4 LX80
> part; varying the following parameters (all "utilization" parameters
> were between low and medium values, Vccint was varied between 1.1V and
> 1.3V):
>
> Vccint
> CLB Usage
> FIFO Usage
> RAM usage
> DSP block usage
> Amount of air flow
>
> What I found is that for every "configuration" I tried the ratio of
> Vccint_new/Vccint_old was almost exactly equal (equal at least to the
> precision of a mW) to the ratio of Power_new/Power_old (where the
> Vccint
> values are between 1.1 and 1.3 and Power_{new,old} refers to only the
> power
> reported as dissipated on the Vccint rail.
>
> Could you please shed some light on the behaviour described above? Are
> Paul and I simply doing something completely wrong with the power
> estimator?
>
> In order to avoid coming off as simple minded, I will refrain from any
> speculation on my side.
>
> Thanks,
> Ljubisa Bajic
> ATI Technologies
>
>
> Austin Lesea <[email protected]> wrote in message news:<[email protected]>...
> > Paul,
> >
> > It does change (with V), as is shown by the predictor.
> >
> > And yes, we do use Vccint. We also use Vccaux.
> >
> > Nothing is ever as simple as it first seems.
> >
> > The devil is in the details, and telling you how it works would just
> > allow you to copy it, and improve your own estimator.
> >
> > Austin
> >
> > Paul Leventis wrote:
> >
> > > Hi Austin,
> > >
> > >
> > >>Since we power the pass gates from Vccaux through a band gap
> > >
> > > referenced
> > >
> > >>supply for the entire interconnect, many simple minded formulas that
> > >
> > > you
> > >
> > >>may come up with will not apply.
> > >
> > >
> > > Excuse my simple-mindedness, but I am having trouble understanding.
> > > You have no circuitry powered off the actual VccInt rail? Your routing
> > > buffers, LUTs, DSPs, RAMs and other hard-IP blocks do not use VccInt
> > > but rather run off the regulated VccAux-driven supply?
> > >
> > > Yes, I will concur that simple rules-of-thumb are never quite true in
> > > practice, and depend on exact circuits used. But are you suggesting
> > > that your supply current doesn't change with voltage? At all?
> > >
> > > Paul Leventis
> > > Altera Corp.
> > >

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  #18 (permalink)  
Old 05-03-2005, 11:31 PM
Brendan Cullen
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Paul has a point when he says that changing Vccint should cause a change in
Iccint. This is in our plans for the Web Power Tool (WPT). When we have
sufficient silicon-based data we will add the appropriate modelling to the WPT.

Changing Vccint (in V4) does also affect the sub-threshold leakage current -
though our measurements and analysis todate suggest it is not the simple square
relationship that Paul suggests. Again - we are continuing with our analysis -
which will be reflected in time in the WPT if (and only if) the effect is
significant. (It's of no benefit to the WPT user for us to model current
variations due to certain small effects if the normal variation from part to
part will swamp such tiny improvements.)

Brendan

"Paul Leventis (at home)" wrote:

> Hi Brendan,
>
> > In terms of "PVT" - Process, Voltage & Temperature : In the WPT currently
> > you can, for V4 FX devices, vary Vccint and the ambient temperature.

>
> When I enter 1.25V vs. 1.20V in WPT 4.1, I'm given 687 mW vs. 660 mW of
> VccInt static power for a LX80, in addition to the 234 mW of VccAux power.
>
> Similarly, for some random amount of logic utlization, I get 2727 mW vs.
> 2618 mW of dynamic power.
>
> It seems to me that all the tool is doing is increasing the V in P = VI.
> However, increasing V should (a) increase dynamic current draw roughly
> linearly and (b) increase sub-threshold leakage by the square of 1.25/1.2.
> Neither of these effects appear to be modeled.
>
> Regards,
>
> Paul Leventis
> Altera Corp.


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  #19 (permalink)  
Old 05-04-2005, 03:20 PM
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Hi Brendan, Austin and Everyone,

Thanks for addressing my question.

I would just like to add that I have been told in private communication
that
Austin was away on vacation and thus was unable to answer my initial
question, so
I would like to retract the (rash) statement I made in my last posting
about him
not responding.

Thanks for the info,
Ljubisa


Brendan Cullen wrote:
> Paul has a point when he says that changing Vccint should cause a

change in
> Iccint. This is in our plans for the Web Power Tool (WPT). When we

have
> sufficient silicon-based data we will add the appropriate modelling

to the WPT.
>
> Changing Vccint (in V4) does also affect the sub-threshold leakage

current -
> though our measurements and analysis todate suggest it is not the

simple square
> relationship that Paul suggests. Again - we are continuing with our

analysis -
> which will be reflected in time in the WPT if (and only if) the

effect is
> significant. (It's of no benefit to the WPT user for us to model

current
> variations due to certain small effects if the normal variation from

part to
> part will swamp such tiny improvements.)
>
> Brendan
>
> "Paul Leventis (at home)" wrote:
>
> > Hi Brendan,
> >
> > > In terms of "PVT" - Process, Voltage & Temperature : In the WPT

currently
> > > you can, for V4 FX devices, vary Vccint and the ambient

temperature.
> >
> > When I enter 1.25V vs. 1.20V in WPT 4.1, I'm given 687 mW vs. 660

mW of
> > VccInt static power for a LX80, in addition to the 234 mW of VccAux

power.
> >
> > Similarly, for some random amount of logic utlization, I get 2727

mW vs.
> > 2618 mW of dynamic power.
> >
> > It seems to me that all the tool is doing is increasing the V in P

= VI.
> > However, increasing V should (a) increase dynamic current draw

roughly
> > linearly and (b) increase sub-threshold leakage by the square of

1.25/1.2.
> > Neither of these effects appear to be modeled.
> >
> > Regards,
> >
> > Paul Leventis
> > Altera Corp.


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  #20 (permalink)  
Old 05-04-2005, 04:32 PM
Austin Lesea
Guest
 
Posts: n/a
Default Re: Virtex 4 Power consumption

Ljubisa,

No offense taken. I am pleased that your questions have been adequately
addressed.

My niece had her wedding in Kauai over the weekend, so we flew out
Friday morning, and flew back Monday.

Wasn't nearly long enough to be in paradise! But I am slightly more
mellow than usual just due to the sun, beaches, good friends, family and
a few glasses on champagne.

Austin

[email protected] wrote:

> Hi Brendan, Austin and Everyone,
>
> Thanks for addressing my question.
>
> I would just like to add that I have been told in private communication
> that
> Austin was away on vacation and thus was unable to answer my initial
> question, so
> I would like to retract the (rash) statement I made in my last posting
> about him
> not responding.
>
> Thanks for the info,
> Ljubisa
>
>
> Brendan Cullen wrote:
>
>>Paul has a point when he says that changing Vccint should cause a

>
> change in
>
>>Iccint. This is in our plans for the Web Power Tool (WPT). When we

>
> have
>
>>sufficient silicon-based data we will add the appropriate modelling

>
> to the WPT.
>
>>Changing Vccint (in V4) does also affect the sub-threshold leakage

>
> current -
>
>>though our measurements and analysis todate suggest it is not the

>
> simple square
>
>>relationship that Paul suggests. Again - we are continuing with our

>
> analysis -
>
>>which will be reflected in time in the WPT if (and only if) the

>
> effect is
>
>>significant. (It's of no benefit to the WPT user for us to model

>
> current
>
>>variations due to certain small effects if the normal variation from

>
> part to
>
>>part will swamp such tiny improvements.)
>>
>>Brendan
>>
>>"Paul Leventis (at home)" wrote:
>>
>>
>>>Hi Brendan,
>>>
>>>
>>>>In terms of "PVT" - Process, Voltage & Temperature : In the WPT

>
> currently
>
>>>>you can, for V4 FX devices, vary Vccint and the ambient

>
> temperature.
>
>>>When I enter 1.25V vs. 1.20V in WPT 4.1, I'm given 687 mW vs. 660

>
> mW of
>
>>>VccInt static power for a LX80, in addition to the 234 mW of VccAux

>
> power.
>
>>>Similarly, for some random amount of logic utlization, I get 2727

>
> mW vs.
>
>>>2618 mW of dynamic power.
>>>
>>>It seems to me that all the tool is doing is increasing the V in P

>
> = VI.
>
>>>However, increasing V should (a) increase dynamic current draw

>
> roughly
>
>>>linearly and (b) increase sub-threshold leakage by the square of

>
> 1.25/1.2.
>
>>>Neither of these effects appear to be modeled.
>>>
>>>Regards,
>>>
>>>Paul Leventis
>>>Altera Corp.

>
>

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