Different behavior for HDMI Hotplug

Dear Community

I have a situation where the HDMI hotplug behavior is different depending on the HDMI monitor used.


I have a unit using the T30 module with latest WEC2013 image. There is a 8" Touch LCD using the RGB interface to the T30 module as main display.
The unit also has a HDMI connector for adding an extra monitor. This does also work, but depends on the monitor used. The registry settings is setup according the guide on Toradex website for dual display. The desktop size is set to a fixed size (matching the setup for the LCD display). Both used HDMI monitor supports that resolution.
I have two diffrent monitors. A 19" and a 10".

When I hotplug the monitor after boot, they both work fine.
But if the 10" monitor is connected before I power the unit on, the LCD display just flicker showing lines and noise but the dekstop is shown nicely on the 10" monitor, With the 19" there are no problems doing this.
Reconnect the cable does not help. Need to power off, remove cable, restart and insert cable again,

I have tried diffrent combination of registry setting like: BootupStyle, HotPlugStyle, HDMIHotplugBehaviour etc. with no luck.

Any idea what could cause this? Any setting or combination to try out?


Hi @TJO,

BootupStyle should be 0x01 and HotPlugStyle should be 0x11
By default the system tries to use the same PLL as a clock source for both LCD and HDMI, but since the HDMI requires much more precise clock, the PLL has to be adjusted, so the exact clock on the LCD will be slightly changed.

It’s strange though that the behaviour is different depending if the 10’’ monitor is plugged in from beginning or attached later.

Maybe something different in the behavior on how the PLL frequencies are initialized.

Is the Splash Screen still visible correctly while booting with the 10’’ connected? or is it corrupted from the start? Maybe it gets corrupted only on the switch to Desktop output?

You can also try the “forcePLLD” registry setting (there is also a similar setting in the splashscreen config block section).
Setting this to 1 forces the LCD and HDMI to use separate PLLs (increasing power consumption, but maybe solving the issue)


Thanks for the feedback. I will try forcePLLD as soon I can.

The splash screen is disabled in the boot config, but it seems the LCD starts flicker as soon I switch it on.