HDMI Handshake bug when motherboard in legacy c... | Geekworm's Forum

HDMI Handshake bug when motherboard in legacy compatibility mode

TheDreadPirate
9/12/26, 12:53 AM

I updated my motherboard's BIOS, Asus X470 Crosshair Hero VII WIFI, and when it finished flashing and rebooted the motherboard reported an issue booting with code B2 with a white GPU light. Researching this suggested this was due to a failure to initialize the GPU. One of the possibilities was a HDMI handshake issue when legacy compatibility is enabled in the BIOS (the default post-flash).

I connected my Intel Arc GPU to my TV via HDMI and it booted up without issue. Once I restored the BIOS config from a backup, which disables legacy compatibility, I was then able to boot normally when my Intel Arc GPU is connected to the HDMI port on the PIKVM (Geekworm KVM-A8 w/RPi 4B).

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HH

Harry Huang Admin Staff member
9/15/26, 11:45 AM

Hi,

Thank you for sharing your detailed findings and the workaround.

The KVM-A8 runs the open-source PiKVM OS. Unfortunately, we are currently unable to provide fixes or modifications to the PiKVM OS itself. For software-level compatibility issues, we recommend reporting the issue to the PiKVM open-source community for further investigation.

When Legacy/CSM compatibility mode is enabled, the motherboard or GPU may use a default HDMI output of 1080p at 60 Hz or higher during the boot process. This startup video signal may not be compatible with the KVM-A8, which could prevent the HDMI handshake from completing correctly and cause the GPU initialization error you observed.

Based on your test results, disabling Legacy/CSM compatibility mode and using UEFI mode appears to be an effective workaround for this particular combination of motherboard, Intel Arc GPU and KVM-A8.

We appreciate you documenting this information, as it may also help other users experiencing a similar issue.

Best regards,

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