PCI lane sharing on X370 Gaming K4
Printed From: ASRock.com
Category: Technical Support
Forum Name: AMD Motherboards
Forum Description: Question about ASRock AMD motherboards
URL: https://forum.asrock.com/forum_posts.asp?TID=4870
Printed Date: 18 May 2024 at 9:22pm
Software Version: Web Wiz Forums 12.04 - http://www.webwizforums.com
Topic: PCI lane sharing on X370 Gaming K4
Posted By: Radical_53
Subject: PCI lane sharing on X370 Gaming K4
Date Posted: 17 Apr 2017 at 12:27am
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" rel="nofollow - Hi! I started using this board some days ago, first with bios 1.50, now with 2.10. Right now, my issue is that my graphics card only runs at PCIe 8x instead of 16x. It's sitting in the second PCIe slot, the first PCIe 16x slot, with no other cards installed apart from a SSD in M2-1. I'm also using 4 SATA devices. Now, from what I get out of the manual, only the second PCIe 16x slot should lower its speed to 8x if it's being used with some "smaller" CPU. I'm using a Ryzen 1700X though. I tried various things like re-seating the card, clearing/defaulting the bios settings, making sure Windows had all the drivers it needs. No change. Any ideas? The only thing left would be either a hardware defect of the board or the graphics card (which worked fine on my previous X99 board). Thanks in advance!
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Replies:
Posted By: Radical_53
Date Posted: 21 Apr 2017 at 7:56pm
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" rel="nofollow - Nobody? Something "official" would be great :D From what I can tell so far, as I just tested a second CPU, it's either the board or the graphics card. Graphics card was working fine on the board I used before this one though.
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Posted By: datonyb
Date Posted: 21 Apr 2017 at 10:44pm
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" rel="nofollow - ok so looking at the board the first long (x16) slot away from the cpu yes ? right this may be due to the setting in the bios there is an option to manually configure the two large pcie slots to auto/x16/x8+x8 i have read of some issues with this setting depending on what card or cards were being used eg one builder tried the new build directly with two cards and the bios was preset to x16 so it wasnt working maybe your bios is set to x8+x8 which is forcing the hardware to become a x8 slot i think most later bios were set at auto (or changed from choice of x16/x8 only to auto) to prevent any issues with first booted new systems ------------- [url=https://valid.x86.fr/jpg250]  [/url]3800X, powercolor reddevil vega64, gskill tridentz3866, taichix370, evga750watt gold |
Posted By: Radical_53
Date Posted: 22 Apr 2017 at 4:20am
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" rel="nofollow - Thanks a lot! You don't happen to remember how that option was called? The card sits in the first long slot from the CPU, yes, and it's the only slot populated so far (I haven't used any other slot on this board so far). If you don't remember I'll look through the options one by one.
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Posted By: datonyb
Date Posted: 22 Apr 2017 at 10:20am
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on my taichi its one the 2nd or 3rd tab along in bios without entering my bios i cant give you the flow chart for steps im afraid its not very obvious where to find it either until you see it listed as pcie something something its obvious when you do find it though ------------- [url=https://valid.x86.fr/jpg250] [/url]3800X, powercolor reddevil vega64, gskill tridentz3866, taichix370, evga750watt gold |
Posted By: parsec
Date Posted: 22 Apr 2017 at 12:15pm
What is telling you that your video card is running in x8 mode? The first PCIe 3.0 x16 physical slot (PCIE2) is x16 electrically, meaning 16 PCIe lanes connected to it. The second PCIe 3.0 x16 physical slot (PCIE4) is x8 electrically at all times, and will only have 8 PCIe lanes connected to it. It cannot work at x16 electrically. My X370 Killer SLI/ac board does not have an option to configure the number of electrical lanes connected to the PCIE2 or PCIE4 slots. The PCIe lane allocation is the same as your board's. There really is not any reason to have a UEFI/BIOS option for configuring the number of PCIe lanes active on the PCIE2 slot on our boards, since they are either x16 with one card, or x8 with two. Also, why would the default setting of such an option be x8 for the PCIE2 slot? The PCIE4 slot being x8 electrically by design further makes such an option useless. The X370 Taichi board also has the same PCIe 3.0 electrical lane allocation for the PCIE2 and PCIE3 slots (different numbering on the Taichi), but includes a PCIe 2.0 x16 physical, x4 electrical slot. I'm skeptical that the X370 Taichi board's UEFI has one or more options to configure the electrical lane allocation, as again the hard wiring of the electrical lanes to each slot makes those options worthless. The manuals for these boards are already out of date compared to the latest UEFI versions, so checking them is no help. There have been in the past options for setting the PCIe generation support, such as 3.0 and 2.0, but that is independent of lane allocation. If you feel certain that your video card is running in x8 mode, then given the things you've done to fix it, it's either the card or the board. Testing with a different video card would be good if possible. ------------- http://valid.x86.fr/48rujh" rel="nofollow"> 
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Radical_53 wrote:Posted By: Radical_53
Date Posted: 22 Apr 2017 at 5:11pm
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Well, so far any program I tried reported 8x to me: GPU-Z 1.20, HWInfo64 5.51-3141 for example. What you're saying was how I understood it, so either the board is defective, thinks that there's a second card installed in PCIe 4 or the card itself is faulty. I already ordered a different graphics card to test this. @datonyb: If you happen to find it, please let me know. I'll check my bios again, thanks.
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Posted By: datonyb
Date Posted: 22 Apr 2017 at 9:35pm
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" rel="nofollow - ho hum so in responce (again) please find below exactly what i described in my answer the taichi DOES IN FACT HAVE THE BIOS SWITCH 2nd set of bios pictures down the linked page 2nd picture in the set clearly showing the switch for 1x16 or 2x8 and below it auto and what i thought i quite clearly said was a suggestion to check this is not causing the problem by being set to 2x8 why it may be set to that we dont know we do know that a lot of am4 board were being sent back to dealers, maybe the board was a returned one resold by a dealer who knows ? what i do know is that before writing off the board as defective, is it that much of an issue to just go and check ? skeptical you may be parsec but once again i have showed that i dont just invent things ! heres the link of my imaginary bios setting http://www.tomshardware.co.uk/asrock-x370-taichi-amd-ryzen-am4-atx-motherboard,review-33826-2.html ------------- [url=https://valid.x86.fr/jpg250] [/url]3800X, powercolor reddevil vega64, gskill tridentz3866, taichix370, evga750watt gold |
Posted By: parsec
Date Posted: 22 Apr 2017 at 10:45pm
Well thanks for posting that link! You could have gone into the UEFI and did a simple F12 screenshot to a USB flash drive and posted the picture, right? Further in what way have you once again showed that you don't invent things? If you read my post above, I said I was skeptical that the option was there. Not that it did not exist. As I predicted, when I said if the option exists, it would be set to 1 x 16 by default. ------------- http://valid.x86.fr/48rujh" rel="nofollow">
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Posted By: parsec
Date Posted: 22 Apr 2017 at 11:14pm
I can tell you that my X370 Killer SLI/ac board with a GTX 1060 is shown as PCIe 3.0 x16 in HWiNFO64. So something is clearly not right. Please try the various settings of the PCIe x16 switch option. We can't tell what the other settings besides Auto are yet, so I cannot suggest which one should be used. I have not seen another post about this issue with the X370 Taichi board yet. Apparently datonyb does not have this problem with his RX 480, but he did not say either way. In general we have occasionally seen issues with x8 instead of x16 connections with some video cards with different boards. Sometimes a UEFI/BIOS clear is the fix, but you've tried that already. When the situation is not one of limited PCIe lanes, PCIe slots not being x16 electrically, or a UEFI setting, the cause and fixes tend to be mysterious, which is why this can be a difficult issue to deal with. ------------- http://valid.x86.fr/48rujh" rel="nofollow">
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Posted By: Radical_53
Date Posted: 23 Apr 2017 at 12:45am
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" rel="nofollow - Yes, well I'm not on the Taichi. This is the Gaming K4, one of the two cheaper X370 offerings. On my board, there's nothing like "AMD PBS", but only "AMD CBS" under the "advanced" tab. I will try another long & thorough CMOS clear. Is there anything that can be done for a bios flash? I've had boards that allowed for a different bios flashing method, usually started from DOS, which could result in a better and more complete flash (the short/normal method would only update parts of the bios, the other one would re-write everything). Just another idea. After that I'll hope the other GPU arrives here quickly, as I would love to get around the hassle to return the board.
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Posted By: Radical_53
Date Posted: 25 Apr 2017 at 6:15pm
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" rel="nofollow - I just received a small 750Ti graphics card and guess what? It started at PCIe 3.0 16x right away. The mysterious part is that my old platform had issues with PCIe link speed also... there, it dropped all the way down to 4x though.
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Posted By: datonyb
Date Posted: 25 Apr 2017 at 7:43pm
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well the plot thickens i did look and my rx480 reports in gpuz bus interface pcie x13 3 @x16 but then it fluctuates between 1.1 and 3 on idle it seems to stay at 1.1 and when i click the ? and run small render test it stays on 3 incidently also i checked my bios and my options have changed from the link i posted now i have options of auto gen1 gen2 very confusing http://smg.photobucket.com/user/datonyb/media/170423142649_zpshxsh5d5l.png.html" rel="nofollow">  ------------- [url=https://valid.x86.fr/jpg250] [/url]3800X, powercolor reddevil vega64, gskill tridentz3866, taichix370, evga750watt gold |
Posted By: Radical_53
Date Posted: 26 Apr 2017 at 3:26am
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That's a totally different animal. What you're experiencing is nothing but power saving working correctly :) It stays at 16x. Mine was at 8x with this board, and with a different GPU & board even at 4x. Whatever I do to these busses...
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Posted By: clubfoot
Date Posted: 26 Apr 2017 at 6:06am
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" rel="nofollow - Does your 480 have dual BIOS? Check the switch position should be A. ------------- https://valid.x86.fr/1tkblf" rel="nofollow"> 
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