[MinnowBoard] Minnowboard and a standard Nvidia GPU?

[John 'Warthog9' Hawley]

On 07/15/2015 08:42 AM, Ashot Arshakyan wrote:
> Hello. I have a project where I need to render thousands of OpenGL
> frames each second by using a x86 based PC and a typical high end NVidia
> GPU.
> The problem is I have a pretty limited space for the electronics of the
> device I'm working on so I was hoping I could use a single board PC
> instead of using a mini ATX.
> SInce the main rendering job is done on the GPU, I thought the
> Minnowboard CPU would be fast enough for the job. What are your thoughts?
> Now I just need to know how I can connect a standard GPU to Minnowboard.
> I'm thinking of powering the GPU with a flat 12V 30A power supply
> instead of ATX to again save some space.

So there's a couple of things you should be aware of while pondering
this.  It *MIGHT* work, but you'll need to consider that modern graphics
cards use a LOT of bandwidth for moving data in and out of the graphics
card.  They usually employee 16 lanes of PCI-e, which at it's oldest and
slowest is about 4GByte/s.  So there's two potential issues here:
	1) The MinnowBoard only has a single lane of PCI-e v2
	   available for use through the high speed expansion
	   header.  This gives you a maximum throughput of
	   about 500MByte/s

	2) *MANY* graphics cards won't negotiate their PCI-e
	   lanes down to the point where it will work in a x1
	   connector.  This is mostly an assumption from the
	   manufacturers that the card would never be used in
	   such a slot.  Case in point when we tried to get a,
	   admittedly rather high end, graphics card working on
	   the MAX on April 1st this year, it didn't work as
	   the card couldn't negotiate down to a single PCI-e
	   lane

The only way to overcome 2, that I can think of, is to put a PCI-e
switch on the bus that can provide 16 lanes, but only upstream via 1.
This still limits your maximum bandwidth to 500MByte/s though, but it
should get you past the lane negotiation issue.  That's a substantial
amount of work though, and likely a need for a custom lure to be built
to accommodate it.  Just some thoughts.

- John 'Warthog9' Hawley