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Visitor mniyas
Visitor
416 Views
Registered: ‎05-21-2018

Device view is not showing proper for different parts of Artix 7 family

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I've ported one legacy design to Artix 7 device xc7a35tcsg324 and it is utilizing 48% of LUTs. Device view also shows appropriate.

xc35t.png

Since it is using only 48% of LUTS, I tried to port to xc7a15tcsg324 and the timing result is exactly as above device.

LUT % is increased to 96% as expected. But in the device view, occupied slices are only around 50% as similar to previous device.

xc15t.png

I'm expecting the device view as almost fully occupied.

Since it is showing only half the Slices occupied, my worry is whether tool is doing something wrong and how can I trust the tool in this family?

What is the reason behind both device shows same Device view?

Since xc7a15t is meeting timing as xc7a35t even though 96% occupied, can I go ahead with xc7a15t as we are not expecting any extra logic for this legacy design?

It is highly appreciated if somebody can get the answer ASAP.

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Scholar u4223374
Scholar
343 Views
Registered: ‎04-26-2015

Re: Device view is not showing proper for different parts of Artix 7 family

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I'm not a Xilinx employee.

 

As far as I know, the XC7A15T, 35T, and 50T are the same die. The larger ones have different dies (may be shared, may not be - I don't know).

 

You can do floor planning exactly as you would on the 35T, as long as you don't exceed the official resources of the XC7A15T.

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Scholar u4223374
Scholar
395 Views
Registered: ‎04-26-2015

Re: Device view is not showing proper for different parts of Artix 7 family

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Luckily, there's nothing wrong here. The XC7A15T is an XC7A35T (ie exactly the same silicon), but when using an XC7A15T Vivado will limit the total resources used. This is fantastic for XC7A15T owners, because you get all the extra (uncounted) routing resources of the larger chip, despite paying for a much smaller chip.

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Visitor mniyas
Visitor
361 Views
Registered: ‎05-21-2018

Re: Device view is not showing proper for different parts of Artix 7 family

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Thanks for the reply. Are you a Xilinx Employee?
I observed the same thing for XC7A50T also.
So, all Artix 7 uses same die?
Since Device View is showing than the actual device, how we will do floor planning/pblocks for the smaller devices?
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Scholar u4223374
Scholar
344 Views
Registered: ‎04-26-2015

Re: Device view is not showing proper for different parts of Artix 7 family

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I'm not a Xilinx employee.

 

As far as I know, the XC7A15T, 35T, and 50T are the same die. The larger ones have different dies (may be shared, may not be - I don't know).

 

You can do floor planning exactly as you would on the 35T, as long as you don't exceed the official resources of the XC7A15T.

Moderator
Moderator
332 Views
Registered: ‎11-04-2010

Re: Device view is not showing proper for different parts of Artix 7 family

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Hi, @mniyas ,

@u4223374 's explanation is correct.

The available number of LUT and Register is correct in the utilization report. 

You can refer to the product table for how many LUT/FF you can use in the device, I don't think such situation will introduce difficulty in your design.

Vivado doesn't have Slice usage limitation for the such device, but the limiation is for total number of LUT/FF and the other logic resource.

You can use more routing resource without further fee for such device.

For floorplanning/pblocks for the smaller devices, the utilization for the pblock can be guidance for you.

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Visitor mniyas
Visitor
303 Views
Registered: ‎05-21-2018

Re: Device view is not showing proper for different parts of Artix 7 family

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This is a really advantage to customers.

I was wondering how the tool was able to meet timing on 15t as 35t when at utilization of 96%. Normally if utilization is >80%, I've observed difficult to meet timing on other devices. So for estimations, we used to take only 80% of the resource for account. But for 15t and 35t we could take as 100% as the die size is big and routing will not be an issue.

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Moderator
Moderator
301 Views
Registered: ‎11-04-2010

Re: Device view is not showing proper for different parts of Artix 7 family

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Yes, for such device, utilization 96% is just the statistics number with a defined limitation, and the actual utilization is far less than 96%.

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