Supermicro server default VESA 1920x1080 too fast for PiKVM frame grabber #1110

New issue

Open

opened 2026-02-20 14:11:11 -05:00 by deekerman · 0 comments

deekerman commented

2026-02-20 14:11:11 -05:00

Owner

Originally created by @hex3262 on GitHub (Feb 15, 2026).

Describe the bug
Standard Supermicro graphics card with default Debian does not work with PiKVM. I am reporting the problem here and offering an acceptable solution, as I spent quite a lot of unnecessary time trying to fix the problem in the wrong places. Among other things, I thought for a long time that it was due to EDID configuration mismatches or to a buggy VGA-to-HDMI converter. So I unnecessarily purchased and tested a whole range of converters. After finding my solution in a completely different place, it's clear in retrospect that all VGA-to-HDMI converters work fine. I hope this report helps others avoid the trouble I had.

To Reproduce
Steps to reproduce the behavior, like:

Supermicro server with ASPEED graphics board running default Debian 12 or 13
PiKVM
Connect Supermicro VGA output via an arbitrary VGA-to-HDMI converter to the PiKVM's HDMI input
Open PiKVM Web interface and select KVM
All you see is "< NO SIGNAL >"

Expected behavior
The Supermicro server can be managed through PiKVM as if it were natively connected to a monitor.

Desktop

OS: Debian or Fedora
Browser: Firefox or Chrome
Version: current as of the day of writing

PiKVM info:

Raspberry Pi board version RPi 4
PiKVM platform v3-hdmi
Video capture type CSI bridge
KVMD version kvmd 4.2-1, kvmd-fan 0.30-1, kvmd-oled 0.27-1, kvmd-platform-v3-hdmi-rpi4 4.2-1, kvmd-webterm 0.50-1
uStreamer version ustreamer 6.12-1
Linux kernel 6.6.21-4-rpi

Additional context
journalctl -u kvmd -f:
CAP: Using capture type: single-planar
CAP: Using input channel: 0
CAP: Detected DV-timings: 1920x1080p60.00, pixclk=148500000, vsync=45, hsync=280
CAP: Using resolution: 1920x1080
CAP: Using format: UYVY
CAP: Querying HW FPS changing is not supported
CAP: Using IO method: MMAP
CAP: Requested 6 device buffers, got 6
CAP: Can't start capturing: Invalid argument
CAP: Capturing stopped

By the way
The same PiKVM works flawlessly with many other systems at 1920x1080-60.

Solution/Workaround
It is finally assumed that ASPEED's default VESA 1920x1080 VGA signal just is a bit too fast for PiKVM's frame grabber. The only quick and easy solution/workaround was to forego the maximum resolution and instead choose the slightly lower resolution of 1680x1050. It should be mentioned at this point that the default Debian installation always selects the maximum possible resolution for the console, which here is 1920x1080. This is configured in /boot/grub/grub.cfg:
set gfxmode=auto

To change the console resolution to 1680x1050 do the following:

Edit /etc/default/grub, uncomment GRUB_GFXMODE and set it to
GRUB_GFXMODE=1680x1050
Run update-grub
Reboot
Enjoy the now functional PiKVM web interface, with the only downside being a slightly lower screen resolution than theoretically should be possible.

Final
Another solution could be to select 1920x1080-45 in GRUB as GFXMODE, but this resolution apparently does not exist. The only unanswered question remains why all the other tested 1920x1080 graphics boards work without problem along with PiKVM, but just Supermicro's ASPEED does not. And the line "CAP: Querying HW FPS changing is not supported" is also reported on correctly working systems, so this probably is not a hint to the real underlying problem.

Originally created by @hex3262 on GitHub (Feb 15, 2026). **Describe the bug** Standard Supermicro graphics card with default Debian does not work with PiKVM. I am reporting the problem here and offering an acceptable solution, as I spent quite a lot of unnecessary time trying to fix the problem in the wrong places. Among other things, I thought for a long time that it was due to EDID configuration mismatches or to a buggy VGA-to-HDMI converter. So I unnecessarily purchased and tested a whole range of converters. After finding my solution in a completely different place, it's clear in retrospect that all VGA-to-HDMI converters work fine. I hope this report helps others avoid the trouble I had. **To Reproduce** Steps to reproduce the behavior, like: - Supermicro server with ASPEED graphics board running default Debian 12 or 13 - PiKVM - Connect Supermicro VGA output via an arbitrary VGA-to-HDMI converter to the PiKVM's HDMI input - Open PiKVM Web interface and select KVM - All you see is "< NO SIGNAL >" **Expected behavior** The Supermicro server can be managed through PiKVM as if it were natively connected to a monitor. **Desktop** - OS: Debian or Fedora - Browser: Firefox or Chrome - Version: current as of the day of writing **PiKVM info:** - Raspberry Pi board version RPi 4 - PiKVM platform v3-hdmi - Video capture type CSI bridge - KVMD version kvmd 4.2-1, kvmd-fan 0.30-1, kvmd-oled 0.27-1, kvmd-platform-v3-hdmi-rpi4 4.2-1, kvmd-webterm 0.50-1 - uStreamer version ustreamer 6.12-1 - Linux kernel 6.6.21-4-rpi **Additional context** journalctl -u kvmd -f: CAP: Using capture type: single-planar CAP: Using input channel: 0 CAP: Detected DV-timings: 1920x1080p60.00, pixclk=148500000, vsync=45, hsync=280 CAP: Using resolution: 1920x1080 CAP: Using format: UYVY CAP: Querying HW FPS changing is not supported CAP: Using IO method: MMAP CAP: Requested 6 device buffers, got 6 CAP: **Can't start capturing: Invalid argument** CAP: Capturing stopped **By the way** The same PiKVM works flawlessly with many other systems at 1920x1080-60. **Solution/Workaround** It is finally assumed that ASPEED's default VESA 1920x1080 VGA signal just is a bit too fast for PiKVM's frame grabber. The only quick and easy solution/workaround was to forego the maximum resolution and instead choose the slightly lower resolution of 1680x1050. It should be mentioned at this point that the default Debian installation always selects the maximum possible resolution for the console, which here is 1920x1080. This is configured in /boot/grub/grub.cfg: set gfxmode=auto To change the console resolution to 1680x1050 do the following: - Edit /etc/default/grub, uncomment GRUB_GFXMODE and set it to GRUB_GFXMODE=1680x1050 - Run update-grub - Reboot - Enjoy the now functional PiKVM web interface, with the only downside being a slightly lower screen resolution than theoretically should be possible. **Final** Another solution could be to select 1920x1080-45 in GRUB as GFXMODE, but this resolution apparently does not exist. The only unanswered question remains why all the other tested 1920x1080 graphics boards work without problem along with PiKVM, but just Supermicro's ASPEED does not. And the line "CAP: Querying HW FPS changing is not supported" is also reported on correctly working systems, so this probably is not a hint to the real underlying problem.