B650M-CX R2.0 USB device causes boot hang
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=113567
Printed Date: 29 Aug 2026 at 2:06pm
Software Version: Web Wiz Forums 12.04 - http://www.webwizforums.com
Topic: B650M-CX R2.0 USB device causes boot hang
Posted By: omnipotato
Subject: B650M-CX R2.0 USB device causes boot hang
Date Posted: 29 Aug 2026 at 4:17am
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Board: ASRock B650M-CX R2.0 BIOS version: 3.50 Issue: System hangs at POST when certain USB devices are plugged in during boot. Symptom is either the ASRock logo hanging with no spinner, or a black screen with a blinking white underscore (no bootable device found). Devices involved: Fujitsu ScanSnap scanner (USB 2.0) NexiGo webcam (USB 2.0) Troubleshooting so far: 1. Disabled Quick Boot - no change. 2. Confirmed via boot menu that only "Windows Boot Manager" is listed as Boot Option #1 - no separate USB boot entry, so this isn't a boot-order issue. 3. USB Configuration screen shows: 4 USB Controllers, 2 Keyboards + 1 Hub detected, XHCI Hand-off: Enabled, USB Mass Storage Driver Support: Enabled. 4. Tried disabling USB Mass Storage Driver Support - no change with ScanSnap alone. Reverted. 5. Disabled XHCI Hand-off - this fixed the hang when only the ScanSnap is plugged in. 6. With XHCI Hand-off still disabled, plugging in both the ScanSnap and the NexiGo webcam together (both on USB 2.0 ports) reproduces the same hang. 7. Tried moving the webcam to a different physical USB port - no change. 8. No "Legacy USB Support" option exists in this BIOS version's USB Configuration screen. Question: Is this a known issue with this board/BIOS version? Is there a BIOS setting I'm missing that controls USB enumeration timeout/behavior with multiple devices at POST? Also considering updating from 3.50 to the latest 4.43 (AGESA ComboAM5 1.3.0.1b Patch A), would that changelog be expected to touch this kind of behavior, or is it unrelated? |
Replies:
Posted By: Xaltar
Date Posted: 29 Aug 2026 at 1:19pm
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I have had a few older USB devices cause issues like this. It's almost always a compatibility issue with the old device. In some cases enabling CSM in the BIOS allows the system to POST normally but CSM needs to be disabled for secure boot so that isn't really an option. In the case of the few devices I have with the same issue I am able to plug them back in once the system has booted and they work just fine. I have 2 devices connected to a USB hub so I just have to connect and disconnect a single USB cable. My problematic devices are an a wireless mouse dongle (USB 2.0) and a USB C microphone (Sennheiser). I have a few USB flash drives that cause the same issue too. Ultimately, USB standards are often not followed properly and newer boards, AM5on AMD and LGA 1200 and newer on intel can be much pickier with some USB devices. Safe boot and TPM 2.0 have made the issue much more apparent as they require CSM mode to be disabled to function. With a lot of messing around and trying different motherboards I was able to get my USB C mic to work but not most of the other problem devices I have. In the end I just went with a USB hub that I can disconnect at boot then reconnect once the OS is loaded. I connect all my problem devices to that to avoid boot issues. I am sure this isn't what you want to hear but it is pretty much the best solution. Effected devices all have firmware of some kind and the system attempts to communicate during POST. Any out of spec code in the firmware causes an issue. Even my USB c 3.2 microphone has an issue with this. It comes down to security changes made more recently to support safe boot etc. FYI, CSM mode contains USB legacy device support, that is why there is no separate option. CSM = Compatibility Support Module. It was great for supporting old hardware and in the past was enabled by default. Since safe boot became mandatory for windows installation it has been set to disabled by default. I see issues like yours pop up all the time ever since. It isn't a board or BIOS problem, it's bad adherence to USB standards on some older devices (and some new ones too). ------------- 
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