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PCIe Root Complex and the PCH

Robert_S_1
Beginner
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Hello All,

I have a question that's been bugging me regarding the PCIe Root Complex and the PCH and I'm hoping someone will be able to help clear things up a bit.

I've always presumed that the PCIe Root Complex was a combination of the CPU and the PCH as they both contain PCIe Root Ports, thereby connecting PCIe devices to CPU/memory. 

It is my understanding from a software point of view that at Bus 0 Device 0 of the PCI config space you have the Root Bridge, that produces Bus 0. On Bus 0 you then have logical PCI - PCI bridges that are the Root Ports, which PCIe devices are behind. Bus 0 starts in the CPU and crosses the DMI into the PCH which also has Root Ports. 

A line in the 'PCI Express System Architecture' says  "Bus 0 is an internal virtual bus within the Root Complex". This is agrees with what I thought, that both the CPU and PCH are part of the Root Complex as Bus 0 is in both the CPU and PCH.

I then read online regarding the "The Lynx Point chipset is much like current platforms (P55, P67, Z68), a platform controller hub (PCH). It handles all the connectivity of the system, but lacks the main PCI-Express root complex which is instead embedded on the CPU. The chipset does however, include an 8-lane PCIe hub, in order to wire out x4 and x1 expansion slots as well as onboard controllers"

The above makes it sound like the PCIe Root Complex is a 'thing' residing within the CPU.

So I'm just a bit unsure regarding what the PCIe Root Complex is.

I know the Root Complex encapsulates CPU transactions into PCIe packets. I presumed this occurred at the Root Ports, so for example a CPU transaction to a PCIe sound card connected to the PCH, when does this become a PCIe transaction? Is it in the uncore part of the CPU, or is it near the Root Port of the PCH.

If anyone could help clear things up for me it would be greatly appreciated.

Kind Regards,

RJSmith92

 

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Harold_G_Intel
Employee
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Hello Robert,

This may be beyond the scope of this forum.

You might try posting this here: http://embedded.communities.intel.com/community/en/hardware

Please see here for support options: http://www.intel.com/content/www/us/en/intelligent-systems/membership/edc-member-benefits.html

Regards, Hal G
Intel(R) Developer Zone Support

http://software.intel.com
*Other names and brands may be claimed as the property of others.

 

 

 

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Robert_S_1
Beginner
992 Views

Hi Hal,

Thanks for the reply.

I have posted at the link you mentioned but wasn't able to post it in the 'hardware' forum, so I have had to post it in the Chinese subforum.

Do you know of anywhere else I could ask?

Kind Regards,

RJSmith92

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Harold_G_Intel
Employee
992 Views

Hello,

You might try sending an email to edc.support@intel.com

If this is a design question you could contact your company's or your distributor's Intel FAE.

Also, you might try this forum: https://software.intel.com/en-us/forums/intel-isa-extensions

Although that is not a direct match, someone on that forum might be able to point you in the right direction.

Regards, Hal

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Robert_S_1
Beginner
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Thanks for the help Hal, much appreciated.

Kind Regards,

Robert.

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Himanshu_T_
Beginner
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Hey Robert, 

If you got the answer for your query please share himanshu.tank@cyberoam.com

Waiting..!!

Thanks,

Himanshu

Skype: himanshu.tank3

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