BIOS BUG - Bottom PCIe Slot Generation 4.0
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=18187
Printed Date: 27 Dec 2024 at 5:40pm
Software Version: Web Wiz Forums 12.04 - http://www.webwizforums.com
Topic: BIOS BUG - Bottom PCIe Slot Generation 4.0
Posted By: apocalypseCow
Subject: BIOS BUG - Bottom PCIe Slot Generation 4.0
Date Posted: 21 Feb 2021 at 11:20am
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I have an x570 Taichi and am attempting to use some external risers to power some extra GPUs. The PCIe GEN 4.0 speeds are not supported by the risers, so I need to lower all of the PCIe socket speeds to 3.0. I have tested on BIOS 3.8 and 4.0, and am UNABLE to change the speed of the BOTTOM PCIe slot (PCIE5) which I know is controlled by the x570 Chipset. The BIOS has several options under the ADVANCED -> AMD PBS Menu related to this: PCIe x16 Bus Interface PCIe x8 Bus Interface Chipset Bus Interface I tested by plugging an NVIDIA 3000 series GPU into ALL of the slots simultaneously. The TOP GPU slot was changed by the BIOS option x16 bus interface. Makes sense, (GEN1-4) all reported correctly in GPU-Z after the change. The MIDDLE GPU slot was changed by the BIOS option 'x8 bus interface'. Also makes sense. Worked as expected. The BOTTOM GPU slot (PCIE5 on the mobo) NEVER CHANGED despite every setting attempt I made. I assumed the "Chipset Bus Interface" would control this slot, but switching it between GEN1-GEN4 had no affect. The slot always reported as PCIe GEN 4.0 in GPU-Z after testing. The other settings mentioned above also had NO AFFECT on the BOTTOM GPU slot. The x1 slots NEVER CHANGED and were on GEN 4.0 despite every option selection. At the moment this is limiting my ability to connect additional GPU's to my x570 board as the remaining x1 slots AND the bottom GPU SLOT seem STUCK on GEN 4.0 PCIe. Is the BIOS broken? I assumed "Chipset Bus Interface" would be the right setting I needed to change, but it did not work. Did this ever work in older versions? I've only tried BIOS 3.8 and 4.0. Can anyone from ASRock please help here? Thanks very much for your time. BIOS Settings Page when selection a Bus Interface:  Setting them all to GEN1 shows the problem clearly:  WHILE running a program on all cards to ensure full load, checking PCIe gen speeds via GPU-Z shows that the 3080 (in BOTTOM GPU SLOT, PCIE5) is locked at PCIe gen 4.0. No combination of settings could change this, I tried them all. 
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