Where to find Chipset, Architecture diagram, &/or PCIe lane assignment specs? (For Z2 G5 SFF W-1250)

[Mr_PeteH]

[UPDATE: correction. System Board has x16, x1, x1, x4 PCIe slots...]

I am having trouble populating the PCIe slots/devices on my Z2 G5 SFF workstation.

AND, I'm having a terrible time finding the needed specs! Used to be pretty easy to find:

• What chipset is used with this CPU (Xeon W-1250)?
• What system board does HP include, and what are its specs?
• What PCIe slot / lane limitations are there?

Searching hasn't helped:

• I find NOTHING in the HP website, nor any of the manuals.
• ark.intel.com only says the W-1250 supports PCIe 3.0 x16 lanes ... presumably that's directly, for video PCIe card.
• And google has been useless.

Here is what I've learned through experience:

• The system board has four physical slots (x16, x1, x1, x4), plus an x1 for WiFi, and 2 x4's for NVMe
• Comes with one NVMe x4 already filled.
• I can't populate all slots, period.
• Just now learned if both NVMe are in use, and disabled nVidia card is activated, the second NVMe literally disappears.

Pointers to authoritative info would be much appreciated. NOTE: apparently the specific CPU does matter.

[Bill_To]

Hi @Mr_PeteH 

Welcome to the HP Forum.

You have probably looked at the following document.

Check this PDF Service Guide for your PC.

HP do not provide the same platform detail usually provided by retail MB manufacturers. 

This CPU is limited to 16 PCIe lanes ( I am surprised!). I can't find anything related to what chipset this CPU works with. So it is not possible to check additional PCIe lanes offered by the chipset.

It looks like you have some chipset PCIe lane and CPU lane switching happening.

Okay, I found the chipset (Comet Lake) at this Link. This chipset has 24 PCIe lanes.

Regards

[Mr_PeteH]

Thanks, @Bill_To
Yes I read the service guide. It doesn't mention any of this, as you saw.

I also knew the W-1250 is Comet Lake -- that's listed at ark.intel.com

But Comet Lake isn't a chipset. It's a CPU generation.

What led you to decide Comet Lake chipset in this case is W480? There are nine different 400 series desktop chipsets 😉

https://ark.intel.com/content/www/us/en/ark/products/series/201843/intel-400-series-desktop-chipsets...

Interesting. I can't find a direct answer, but found a very helpful generic tool at the Intel site, here .

At least in this compatibility tool, 100% of compatible motherboards for the W-1250 use the W480 chipset. Better than nothing.

We still are limited in our understanding. For example, the W480 chipset supports 8 SATA drives. The Z2 G5 only supports four. But that's not too surprising: someone has to decide what to include on a particular system board.

[Mr_PeteH]

Oh, and remember: there's a difference between CPU lanes (usually for video) and chipset lanes (usually for system board slots, storage and more.)

This is why knowing something about the system hardware configuration is rather crucial. Rather hard to know what devices will work in a Z2 if we don't know what is available. And hard to diagnose configuration issues.

(In my case, my second mirrored NVMe suddenly disappears when the nVidia card is activated 😞 ... I'm sure it has to do with PCIe limitations, but I have no idea what those limits are, specifically.)

I've found more detail along the way. The (obscure due to an Intel website error) series 400 chipset data sheet vol 1 of 2 provides some extra insight. In pp 19-20, the W480 "Flex I/O" channels are described, including how various functions can or do overlay one another. A few initial facts:

• Yes the chipset supports "up to" 24 PCIe lanes
• However, those lanes are largely overlaid/alternately used for a wide variety of OTHER functions.
• In fact, only 3 of the 30 flex channels are always dedicated to PCIe! 

Here are a few of the pertinent overlays, of PCIe lanes NOT used for generic PCIe:

• 8 PCIe lanes are also for NVMe support ("Intel RST for PCIe Storage")
• 2 are for the Ethernet and WiFi ports
• 4 are used for the SATA ports
• 3 for USB 3 (beyond 6 flex channels dedicated to USB 3)

By my count that's 8+2+4+3 = 17, leaving 7 unencumbered PCIe lanes. 

Since we have 16 lanes direct to the CPU for the x16 video slot, We're only 3 lanes short for the x8 and 2 x1 slots.

The remaining puzzle is which of the above flex channels are overlaid on the PCIe slots?

I could wish it were the three additional USB 3 ports -- there are SO many, I can't imagine ever needing them 🙂🙂

UPDATE: besides the x16 video direct to CPU, the other slots are x1, x1, x4. SO the spare 7 lanes "ought" to be enough, given sufficient flexibility.

The hard part with real-world System Boards and BIOS etc... usually these things are not 100% splittable any way you want. That's one reason PCIe "bifurcation" was invented. So now I just need to learn what the actual interactions are.

[Bill_To]

Hi @Mr_PeteH 

Download and run CPU-Z at this Site. Look at the Mainboard section.

The Mainboard section should ID the chipset.

HP is PCIe lane switching if you lose some PCIe lanes on a different PCIe slot when you populate all PCIe slots.

HP should be allocating available PCIe chipset lanes between all other I/O on your MB (USB, SATA, WIFI, Ethernet).

The chipset also has to connect to the CPU (DMI). This interconnect can use anywhere between X2 up to x8 PCIe lanes.

It looks like the NVME drive connection is sharing PCIe lanes with the limited amount of 16 PCIe lanes from the CPU.  You lose the NVME drive when you connect a PCIe  x16 graphics card.

Regards

[Mr_PeteH]

@Bill_To that's not quite correct. The cpu has x16 lanes (for video) apart from what's available through the chipset.

Good thought on CPU-Z! Not running Windows, but there's an equivalent for Linux-type OS: CPU-X 🙂

So, this is Intel chipset 0697 which apparently IS W480.

The harder part is the system board. HP 8753, "KBC Revision 09.08.23" ... so far I find no info on that at all. 😞

I just connected with HP support. 

1) The Quick Specs do give the chipset: W480

2) Here's a more complete Spec, including updates: https://h20195.www2.hp.com/v2/gethtml.aspx?docname=c06914243&search=HP%20Z2%20SFF%20G5%20Workstation

3) Unfortunately, it does not list interactions. Going to study a bit more...

OK, I have updated my original post and response above. In theory, there should be no issue:

• My PCIe lane count was correct: 7 unencumbered lanes for slots, not including the CPU x16 slot for video
• The remaining slots are x1, x1, x4 == 6 lanes.

What could possibly go wrong? Lots. System Boards usually are NOT 100% flexible with PCIe lanes. But the limitations in this board are not documented.

Time to learn more and/or do some experiments 🙂

[Update, June 3: I am stumped. Instlling the nVidia card causes NVMe slot 2 device to completely disappear. Going for support on this. No idea why.]

[Mr_PeteH · Accepted solution]

OK, I have fully solved my issue, and learned MUCH along the way.

First, a HUGE thanks to HP for setting up a great tech support team, at least on business phone support! My call answered by someone who understood the question, took *ownership* of the issue until solved. That alone has not been seen by me in at least 20 years!

Next: I learned...

* Some issues can scramble BIOS configuration so badly, the system started thinking it had NO display and NO storage.

* If dealing with a wierd issue, best bet is to do BIOS Factory Reset to get to a stable state, and do that before each test.

* My issue: was repeatable on multiple Z2 G5 SFF workstations. With multiple nVidia cards.

* Although I have some PCIe cards advertised everywhere as PCIe2... in reality they are PCIe1! Must dig in at OS level to learn that. (In linux: "lspci -vv")

* HP currently has no tools or utilities that assist in analyzing PCIe card or lane or bandwidth issues. Either a card is visible, or it is not. 😞

The real problem in my case: if a GPU and a particular 2 port ethernet card is installed, then...

* One of the NVMe slots downgrades from PCIe3 to PCIe1

* AND any NVMe storage in that slot is invisible to BIOS, diagnostic tools, and the computer itself

I purchased another 2 port (Intel 82576 / ET platform) NIC card... and suddenly everything works great!