No output: Jetson TX2 Dev. Board connecting to an external 5" display

Robotics & Edge Computing Jetson & Embedded Systems Jetson TX2
1

Hi,

I am working with a Jetson TX2 Development Kit (running Jetpack 3.2) and trying to connect it to an external 5" display with 1440 x 2560 resolution through the HDMI port. But, the display keeps blinking, without any output. Sometimes it shows up just after booting for a second, but then turns off and starts blinking again.

1- Is the resolution not supported?
2- If the resolution is not supported, could we hack and force that resolution?

I am new to Jetson Development, so detailed steps would be highly appreciated.

P.S. The display works fine with my laptop running Ubuntu 16.04.

Best
Debanga

2

Is your cabling purely HDMI through the whole path? If there is anything which breaks the DDC wire (which provides EDID information when the video card queries the monitor for its abilities), then automatic configuration would fail. One example of causing this is an adapter between VGA and HDMI since VGA does not have EDID capability. Another example of a scenario which cannot work is if you added on an adapter to hardware to produce HDMI but did not set up EDID data.

The only modes supported are those modes which EDID query finds. To see the details of every mode the EDID is reporting (and what the driver thinks of those modes) you will want to add this to the Section “Device”:

Option   "ModeDebug"

With this in place the log in “/var/log/Xorg.0.log” will give details of every timing it sees from EDID and what the monitor thinks about that mode.

3

Hi linuxdev,

Thank you very much for your response!

Furthermore, I was exploring and found:
https://elinux.org/Jetson_TX2/r28_Display_debug

If I want to force a resolution, it is mentioned:

  • Forcing edid (This is most likely when your monitor failed to be up due to problematic default EDID)
  1. Prepare a known 256byte EDID.
  2. set use_fallback = true; in tegra_edid_get_monspecs() under edid.c.
  3. fill in the known EDID to default_720p_edid[256].

Do you think if I do the above process (which would be a long kernel compiling process) with a known working monitor (15", 720p default), than I can run the small external monitor (15") afterward?
1- Does it use the resolution of “known working monitor”?
2- Can I use this process to up the “small external” monitor may be in a already supported mode?

Best
Debanga

5

I’m not positive, but I think that patch was under R28.1. It may be that if you use R28.2 the patch is already there…I don’t know.

As for the rest of the steps “it depends”. Is your display currently sending an EDID? If there is no EDID, and you have another monitor which does have EDID, and if that monitor is put in a mode common and acceptable to both monitors and to the driver, then upon switching from one monitor with that EDID to another monitor which does not send EDID, then the mode will probably remain what it was…as a result of the two monitors having that mode in common, then the display should operate correctly until reboot or some other mode change.

You really must start by saying whether you have a monitor without EDID, or if you have a monitor with an EDID which is being rejected. The approach will differ. Also, there may be differences depending on which L4T release you use…I think R28.2 has improved some video aspects and so if your monitor simply has an EDID which isn’t liked by R28.1, then R28.2 might fix it.

One way to see EDID content:

sudo -s
cat `find /sys -name edid`
exit

…if there is hex data, then its nature can be seen by pasting it into http://www.edidreader.com.

If there is hex data, then the note I made in a previous post about adding Option “ModeDebug” to Section “Device” would give you a way to see what the actual driver thinks about the modes presented in EDID. This may also be useful when exploring a different monitor if looking at modes which might work for you.

1 Like
6

Hi linuxdev and debanga88,

First of all, I need to say sorry that the patch for fixing the mode was removed just before rel-28.2 is out due to some issue.(It is in rel-28.2 DP but not officially rel-28.2) However, we put the method of how to fix it in L4T doc.

Please note that this fix is useful but not for all monitor.

cd Linux_for_Tegra/kernel

./nv-enable-hard-coded-kernel-boot-display-mode.sh dtb/tegra186-quill-p3310-1000-c03-00-base.dtb

reflash the device with this dtb.

debanga88,
Please share the log(dmesg) when you bootup with HDMI connected. (Not a hot plug case)