How to know the status of hdmi signal?

Hi all,
We make a customize TK1 board and there is a monitor connected with our two tk1 board.
One board is as primary hdmi source and the other one is backup hdmi source. When the monitor detect no signal from primary hdmi source, it will automatically swith to the backup one. It will switch back when the primary signal is recovered. The issue is that sometimes we find the monitor detect hdmi video loss so it switch to backup and it swich back after a few seconds since it detect the primary hdmi is back. It repeat this process continuously. I check the kernel log of primary TK1 board and couldn’t find any possible error cause no hdmi signal output. The kerenl log is as attachment. I would like to know if there really is no signal output. Is there any register or commands I can check the status of hdmi signal ?
kernel.log (73 KB)

Sorry for late reply.

Have you ever tried a test which puts only one tk1 as HDMI source?

Hi FrankPCP,

Have you clarified the cause and resolved the problem? Or this is not an issue now?
Any result can be shared?

Thanks

Hi kayccc,
We find the H/V sync polarity is always negative. I modify the kernel and let H/V sync polarity be correct value as what edid want. This issue seems fixed. We will do more test.
BTW, someone also find the sync polarity is wrong. Please see the link below.
https://devtalk.nvidia.com/default/topic/1029848/jetson-tk1/tk1-hdmi-video-output-sync-polarity-is-always-negative