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PCI-e revision

Posted: Wed Aug 13, 2014 11:54 am
by hwmartin

Could you please confirm that the mini-PCIe slots present in the MintBox 2 are PCI-e rev. 2.0 compliant?

I see from Intel's documentation that the HM76 provides two PCI-e rev. 2.0 x1 links. The CompuLab system diagram shows the PCI-e revision for the links from the CPU (which are unused) but does not specify the revision for the PCI-e links provided by the PCH.

Also does CompuLab know if a discrete video card can be used with the MintBox 2 if a mini-PCIe to PCI-express adapter, and external 12V power supply for PCI-e power, was used. Something like this product.


Re: PCI-e revision

Posted: Thu Aug 21, 2014 9:00 am
by mbirger
Yes, Intense PC uses PCIe2.0 lanes on chipset and PCIe3.0 PEG from CPU to FACE Module (as optional for external graphics).

Regarding discrete video card - it is possible. The problem is that mini PCIe slot provide 1x PCIe lane which is not enough for external graphics in terms of BW. For that purpose PEG provided.

Re: PCI-e revision

Posted: Thu Aug 21, 2014 7:07 pm
by hwmartin
@mbirger: Thanks for clarifying the PCI-e revision.

On the MintBox 2 block diagram the PCI-e 3.0 x8 and x1 buses from the CPU are shown as unused.

However in your post you implied that the PEG is exposed through a different FACE module. Could you clarify if those buses are available for use with a different FACE module? I interpreted the term "unused bus" to mean that the bus was not available for use at all.

If the bus is present and can be exposed through a FACE module, is that FACE module available for purchase? The FACE module hardware specification lists the FM-XTDM2 with 2 Mini PCI-e interfaces, but I do not see a FACE module that provides more than PCIe 2.0 x1 interfaces.

Re: PCI-e revision

Posted: Sun Aug 24, 2014 1:45 pm
by mbirger
There is no off-the-shelf FACE module with PEG routing and connections. Provided mainly for customers wish to implement their own FACE module.
If required I can connect you with our partner that can develop such module on a subcontractor basis very easily.

Re: PCI-e revision

Posted: Tue Sep 09, 2014 11:24 am
by hwmartin
Thank you for the offer, but I don't think I want PEG enough to pay for a custom FACE module to be developed.

I ordered a mini-PCIe to PCI-e x1 adapter. It will be interesting to see what (if any) performance increase there is with a discrete card on the PCI-e 2.0 x1 link.

Re: PCI-e revision

Posted: Tue Sep 16, 2014 6:09 pm
by hwmartin
Just wanted to follow up on this and share my experience:
Yes, mini PCI-e to external PCI-e adapters do work with the MintBox 2. I tried with an NVidia GT 520M and the performance increase when playing Steam games was very noticeable.

BUT there are some drawbacks to this:
- Intel video will be disabled. As far as I can tell there is no way to enable or use Optimus graphics. When a discrete card is present the Intel graphics are disabled.
- Since you cannot use the Intel video card, the HDMI/DisplayPort outputs on the MintBox do not work. You have to use the video/audio capabilities of your external video card.
- You need to supply 12V to the external adapter for the video card. The MintBox will not provide this for you.
- You also need to manually power cycle the card when you reboot the MintBox. For me this meant instead of rebooting I would shut down the MintBox, power cycle the external graphics card, and then power on the MintBox again.
- You will have an awkward cable sticking out of the MintBox for the external adapter. I ordered an adapter with a flat 30cm ribbon cable that routes nicely out of the chassis below the ethernet ports with zero modification to the MintBox. However, the longer the cable the more clock issues you will have with the PCI-e bus.
- Increased power use. Newer NVidia cards don't use much power when they idle (I've read somewhere around 11W, about what the MintBox draws idle) but when they're in use the power consumption increases dramatically. Low-end cards like the GT 520M are supposed to draw around 30W, the same as a MintBox under full load (with IGP enabled). Mid-range cards like the GTX 650 can draw 70W, and high end cards can easily exceed 100W.

However, there are still a few advantages:
+ No memory used for the IGP, and there is no memory penalty for adding an external GPU (e.g. I can still see and use all 16GB of system RAM).
+ Improved performance.
+ GPU is connected via PCI-e 2.0 x1 link (5GT/s)

A PCI-e 1.0 x16 card has a bandwidth of 40GT/s, so this solution only provides 1/8th the bandwidth a PCI-e 1.0 x16 card would receive. Obviously you are not going to get the full performance out of the discrete card. This article compares the speed increase from putting a video card in an x16 slot versus an x1 slot. Clearly there is the possibility for a large increase in performance from x1 to x16. But I think that the performance gained from the HD4000 to a discrete solution is probably larger, and you're stuck with an x1 link anyway (unless you fund the development of a FACE module with a PEG port).

In conclusion: you can do it, it seems to offer modest performance gains, but in the end it probably isn't worth it. If you want a small system with a powerful video card just build a Mini-ITX system, it will end up being cleaner and more convenient than this solution is.

However, if your interest is in another PCI-e card (e.g. not a graphics card) then you might consider this more viable. Intel video would still work and you would have access to a full size PCI-e 2.0 x1 slot for whatever kind of card you want to install (network, RAID, video capture, etc).