Flexible PCIe risers

EdZ

Virtual Realist
Gold Supporter
May 11, 2015
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just thinking out loud: what about a really simple 'terminator-like' device and a driver? the terminator comes instead of a real pcie device.
e.g. the terminator could be something looping back data on each lane (or across lanes, etc). it must be an active component because it needs to negotiate the pcie version, number of lanes used, TLP length, etc). passive loopback would be too easy :)
so a pcie device with an fpga would do it. the problem is that they are really expensive so killing the whole idea of 'cheap' testing. altera and xilinx might have some nice boards.
unfortunately a cheap(er) x1 device is not an option because most likely we can not say that if one lane has a good quality then all the lanes have and regarding signal integrity this is absolutely an invalid test for multi-lane risers.
Also, having a NIC with enough bandwidth is really expensive, too. a 2x100G NIC doing a loopback would be pretty close to what I am thinking about. (either having a loopback cable or configured for doing loopback on chip level). the problem is not only the expensive NIC but also the CPU required for generating and capturing this amount of data. trafgen could be something like https://trex-tgn.cisco.com/ or http://dpdk.org/browse/apps/pktgen-dpdk/refs/

another option could be to add this feature to an existing videocard driver and write a tool like the Furmark. Or using Furmark itself if it can generate really high traffic with some settings on pcie. Intel's PCM (performance count monitor) or Microsoft's Xperf might give some information about the occupancy of the lanes but I am unaware of any counters like retransmit or so.
This would give you a pass/fail test for a certain situation (the one you perform the test in), but does not tell you much about the riser itself, nor how it will work in other situations. If you know and can the environment in which the riser will be used, this testing is suitable and a lot cheaper than full signal testing.

The benefit to proper 'eye pattern' testing is it tells you not only whether the riser will work, but exactly how much margin you have before it will get out of spec, and how it will go out of spec (which lets you track down which element is failing and how to improve it). For example, you can easily tell the difference between a crosstalk issue (and use the timing to determine exactly where in the riser the crosstalk is occurring) from an impedance mismatch issue. It also gives direct feedback on what's happening during interference testing, so you can track down where signal is 'leaking'.
 

rokabeka

network packet manipulator
Jul 9, 2016
206
231
agreed.

I was hoping to have a reference test environment and compare different risers. My idea failed at the point that comparing them in my environment does not tell anything about their behavior in other environments.

thank you for your comments.

yawacool's test with the connectx-3 has the same problem I was mentioning regarding video cards. this is a nice test, but connectx-3 is a pcie v3.0 x8. so that is valid for testing an x8 riser and the total usage of the pcie lanes should be monitored because if the bandwidth never goes close to the limit then it only proves that there are situations where the riser does not fail.
 
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Ceros_X

King of Cable Management
Mar 8, 2016
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Kmpkt

Innovation through Miniaturization
KMPKT
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Feb 1, 2016
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I've just ordered in these two adapters from Vary Technology and will let everyone know what I think when I get them. I'm especially excited for the M.2 to PCIe 16x adapter, especially in light of the BPlus adapter nearly tripling in price (gougy assholes):



 

lordzahl

Trash Compacter
Feb 7, 2016
54
10
Wo
I've just ordered in these two adapters from Vary Technology and will let everyone know what I think when I get them. I'm especially excited for the M.2 to PCIe 16x adapter, especially in light of the BPlus adapter nearly tripling in price (gougy assholes):



Wow these look excellent.
The homepage also shows some photos of the riser:
http://vary.technology/product/RP33.html
 
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aquelito

King of Cable Management
Piccolo PC
Feb 16, 2016
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Great find, Gen 3.0 and flexible !

Curious about the ribbon technology. Same as 3M Coaxial ?
 

lordzahl

Trash Compacter
Feb 7, 2016
54
10
Great find, Gen 3.0 and flexible !

Curious about the ribbon technology. Same as 3M Coaxial ?
The website says:
The ribbonized format of the axial cable provides a dense and flexible solution without signal attenuation for high speed PCIe Gen3 8Gbps Data Transaction, bidirectional 256Gbps (256GT/sec) for PCI x16, and 16Gpbs (16GT/sec) per PCIe lane.
So it is indeed a coxial ribbon cable. If @Kmpkt cables look good, i also might order one.
 

aquelito

King of Cable Management
Piccolo PC
Feb 16, 2016
887
996
If someone has the possibility to measure the total height of the PCIe connector of a generic riser (contacts + green PCB + blue tape), as well as the minimum bending radius of the ribbon ?

I'm working with a 36mm high case and I have merely 12mm clearance above the PCIe slot.

Thanks !
 
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bledha

Airflow Optimizer
Feb 22, 2017
306
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These are available where I live, a good length, and are a reasonable price - thoughts on the brand?

I have read in some places (not sure if it is true...) that this would only really support PCIe gen 2.0, and there is a maximum length to support gen 3.0 speeds - 20cm. Any truth to this?

I'll try to get a review up as soon as I have these.
Added some to a cart and looked at shipping costs - seem to be nearly as much as the cable itself. Is this true?
 
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stefan33

Average Stuffer
Jan 13, 2017
73
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Also I'm Italian, but I live in Ibiza.... Are you on Hardware Upgrade Forum?
 

bledha

Airflow Optimizer
Feb 22, 2017
306
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Also I'm Italian, but I live in Ibiza.... Are you on Hardware Upgrade Forum?
I am not (yet) an Italian citizen, expatriate. Therefore I am not perfectly fluent in Italian so I am not on that forum.