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dag1
Explorer
Explorer
546 Views
Registered: ‎12-08-2007

x16 PCIe

I am vaguely familiar with PCIe, so I'd like to verify if these are suitable computers for Alveo U250: some of the workstations, such as Dell Precision, have x16 PCIe  which is wired as

four x4

or as

sixteen x1

slots.

They still refer to it as   x16 slot.

I'd like to know if the Alveo U250 works with such slots? if not, what is the exact specification  of slot for Alveo U250, in the data sheet it says Gen 3, PCIe x16 dual width slot but how should it be wired?

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mcertosi
Xilinx Employee
Xilinx Employee
537 Views
Registered: ‎10-19-2015

Hi @dag1

Using the shells provided with the Alveo cards eliminates the need to understand PCIe at a physical level. If you are not familiar with PCIe design, you should start with these. 

The cards are wired up for Gen3x16 and that is what the shell provides. 

Unless specifically configured for bifurcation, the cards will link as Gen3x16. They do not automatically change themselves for bifurcated operation. An example of bifurcation is a Gen3x8x8 link. 

If you see your card coming up in any other configuration than Gen3x16, you likely have a physical problem with the slot or server. 

A dual width slot is referring to the actual card width, the card takes up 2 slots because of its size. 

Are you trying to physically wire something?

Regards,

M

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dag1
Explorer
Explorer
483 Views
Registered: ‎12-08-2007

At the moment I don't have a PC, just the Alveo board. I am not familiar with the concept of "shells". Can you elaborate?

I attach picture of the PCIe slots available on a workstation which I am considering.

You can see that some of the x16 slots are "wired as x4 and some as x1". If I understand correctly it means that the length of the slot can accommodate the Alveo but the number of lanes on such slots will not be 16 but smaller. Some of the other slots it says x16 (without "wired as"), so I think it means that the slot has 16 lanes.

If I want to utilize the Alveo to the maximum extent I should have an x16 with 16 lanes?

 

Screen Shot 2020-04-28 at 19.35.29.png

 

 

 

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mcertosi
Xilinx Employee
Xilinx Employee
430 Views
Registered: ‎10-19-2015

Hi @dag1 

Yes, you'll need a Gen3x16 slot that is dual wide and double rack height to fit a U200, U250, and U280. The u50 is smaller, however requires lots of airflow and should not be used in a desktop.

Make sure you get a card with active cooling if you are putting it in a desktop, otherwise it will overheat and you will void the warranty. 

A shell is the main basis for the acceleration flow with the card. The shell connects PCIe, the satellite controller, the scheduler, the card management system, the QSPI, and the DDR for you. This is done because the hardware is static and those connections will not change. The shell is dynamic, meaning any resources you are not using are not placed in the design, allowing you to use that logic for your acceleration kernel. 

Please see the getting started tutorials and Vitis documentation to read more.

Getting Started

Vitis Documentation 

Regards,

M

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