Beagleboard talk:BeagleBoneBlack HDMI

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Thread titleRepliesLast modified
How to force a resolution012:33, 28 January 2016
Resolution information017:23, 8 May 2014

How to force a resolution

I followed the instructions on this page but noticed that it didn't really mention how to make the changes permanent.

This works for my Samsung LED Monitor S24D300HL.

root@beaglebone:~# tail -n6 /etc/gdm/Init/Default
# Use xrandr!
export XAUTHORITY=`ls /var/run/gdm/auth-for-root-*/database`
export DISPLAY=:0
xrandr --output HDMI-0 --mode 1680x1050

exit 0
JohnWasinger (talk)12:25, 28 January 2016

Resolution information

720x480-16@60 was a supported mode for the HDMI in the 3.8 kernel, and it is a CEA mode with audio. It isn't mentioned in the list of resolutions, though it is referenced further down the page. Has this mode been removed in the newer 3.12/13/14 kernels?

In the "Connecting to a TV or Display" section, there is this line:

"If the board does not see a display connected, it will default to 720x480 resolution and outputs that signal on the HDMI port."

If no EDID information is received (either the display isn't plugged in or the display provides no EDID), the resolution defaults to 1024x768. This is done in the function drm_fb_helper_single_fb_probe() in drivers/gpu/drm/drm_fb_helper.c in the kernel. I only have 3.8/12/13 kernel sources trees handy at the moment, and the default is 1024x768 for all of them. Unfortunately, 1024x768 is not a CEA mode, so audio over HDMI will not be enabled (and no ALSA device will be created in /dev) if the display is not plugged into the BBB at boot.

Hendersa (talk)17:23, 8 May 2014