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5745 Discussions

why Arria II doesn't support x2 PCIe?

Altera_Forum
Honored Contributor I
801 Views

Anyone has any ideas why Arria II doesn't support x2 PCIe? 

I really like Arria II and want to make a system with multple PCIe cards, but x4 lane PCIe switches are very expensive.  

 

 

Thanks.  

Jeff
0 Kudos
6 Replies
Altera_Forum
Honored Contributor I
58 Views

I've tried to use scotch-tape to shield lanes 3->8 of an arria card. It works as a x2 PCIe. "No one" complains anything. :D 

Is there any harm with it?  

 

Jeff
Altera_Forum
Honored Contributor I
58 Views

Hi, 

 

from my understandment PCIE runs in x1, x4, x8 and x16. x2 is possible but is not standard for the Slots on a mainboard. 

 

Card PCIe x1 PCIe x4 PCIe x8 PCIe x16 x1 ok ok ok ok x4 - ok ? ? x8 - - ok ? x16 * * * ok 

On the other side you can use the lanes like you want to :) if the core supports x2 this schould be no problem.
Altera_Forum
Honored Contributor I
58 Views

 

--- Quote Start ---  

Hi, 

 

from my understandment PCIE runs in x1, x4, x8 and x16. x2 is possible but is not standard for the Slots on a mainboard. 

 

Card PCIe x1 PCIe x4 PCIe x8 PCIe x16 x1 ok ok ok ok x4 - ok ? ? x8 - - ok ? x16 * * * ok 

On the other side you can use the lanes like you want to :) if the core supports x2 this schould be no problem. 

--- Quote End ---  

 

 

The thing is in the PCIe compiler wizard, no x2 option is allowed. (x1, x4 and x8 only), and datasheet of Arria also specifies that x1, x4 and x8. No such x2. x2 is only in CycloneIV. I'm not sure wha't the reason behind it.  

 

So what i tried to do was to hack/cheat the PCIe compiler.  

I configure the core to be x8 but actually plug into a "x2 slot" (by masking the pins with scotch tape).  

So far, nothing complains. Data is well-received.
Altera_Forum
Honored Contributor I
58 Views

That is just "problem" of the compiler, the PCIe protocol can negotiate any number of active links. You can use x32 device in x1,x2,x4,x8,x16 slots (of course if the slot is ready to accept larger card) and also you can use x1 device in all larger slots, the protocol will handle the link count negotiation. 

 

Just generate the x4 PCIe and use first two links.
Altera_Forum
Honored Contributor I
58 Views

Hi again, 

 

that´s what I mean as well. If you take a look on some baseboards you will find x16 Slots with only 4 lanes connected. I also found some boards with x4 Slots and only 1 lane connected. I´ve never seen a board with an x2 connector.
Altera_Forum
Honored Contributor I
58 Views

Thanks JacoL and Zizka.  

That info's really useful, as i was not sure how the PHY is decoupled from the Transaction layer.
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