* your mileage may vary

Thursday, 24 April 2014

Beaglebone Black (BBB) HDMI Debian X11/LDE Display Problem ?

I was having trouble to debug a problem related with the bootup process and the LDE GUI display.  I'm not really sure what the problem was or why this worked, but in the end it worked for me. I've posted this in the BBB forum but Google Groups is a headache.

 Configuration / Notes:
•    BBB: Rev A5C
•    Power source: Using barrel connector +/- USB connector
•    Monitor: Samsung S22B300 Sync-master
•    Debian Build: root@beaglebone:# uname -a
=> Linux beaglebone 3.8.13-bone41 #1 SMP Tue Mar 4 22:51:47 UTC 2014 armv7l GNU/Linux
•    uEnv: cat /proc/cmdline
=> console=ttyO0,115200n8 video=HDMI-A-1:1024x768 root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait fixrtc quiet init=/lib/systemd/systemd
•    Good HDMI cable, validated with stock Angstrom & Ubuntu image; GUI works fine with these images
•    Debian configuration tested on separate TV monitor works fine – boots to GUI
•    VNC to Debian display GUI – no problem

Observations / Issue
•    Boot process looks normal, Linux Penguin displays; proceeds to display 
•    “The IP Address for eth0 ….” displays login prompt; auto login continues, screen goes blank and then after about 5 seconds the screen goes into power save mode.
•    Selecting tty2, the screen exits from power save mode and shows login prompt
•    Returning to tty7 the screen is blank and then returns to power save mode
•    echo 0 > /sys/class/graphics/fb0/blank has no impact (as root)
•    Pulled the EDID info following http://elinux.org/Beagleboard:BeagleBoneBlack_HDMI and tried different resolutions with no change in the observations noted above.

Finally, after many tests, google-ing, re-flashing, trying to understand the systemd/init.d/start process (still confused about how the boot process works) , I found some hints here;


In the end, I (warning => use this at your own risk)

sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.backup
sudo apt-get install xserver-xorg-video-fbdev
sudo reboot

and I have the LDE desktop !!!

I’m noticing some errors in /var/logs/Xorg.0.log  related to

FBDEV(0): FBIOPUTCMAP: Invalid argument

,....but I’ll leave that for another day.

///// UPDATE /////
after some further investigations I think I understand what is happening.....
the default xorg.cong file is using the modesetting driver.  For what ever reason the driver could not pull the proper EDID setting from my monitor (Samsung S22B300).  

Check /var/log/Xorg.0.log for clues !!!

The update update above basically swaps out the modesetting driver for the framebuffer driver (fbdev) which works.  Apparently fbdev is slower (but at least it works).

In order to get my monitor to work with the modesetting driver I aligned a valid mode line for my monitor with a valid BBB resolution into my xorg.conf.  

My working xorg.conf

Final note:  => this is for linux 3.8.16, Debian Wheezy.   No luck with 3.13 and Jessie


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