EBC Exercise 19 DSS2 and sysfs

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thumb‎ Embedded Linux Class by Mark A. Yoder

3.2 Kernel‎

Here are some example DSS2 sysfs commands that run on the Beagle xM running the 3.2 kernel. (No BeagleBone Black version yet.)

Play around and see what you can learn.


The framebuffers are in /sys/class/graphics/.

beagle$ ls -F /sys/class/graphics/
fb0@  fb1@  fb2@  fbcon@
beagle$ cd /sys/class/graphics/fb0
beagle$ ls -F
bits_per_pixel  dev      modes            pan        rotate_type  subsystem@
blank           device@  name             phys_addr  size         uevent
console         mirror   overlays         power/     state        virt_addr
cursor          mode     overlays_rotate  rotate     stride       virtual_size

Overlays, Managers and Displays

The overlays, managers and displays are in /sys/devices/platform/omapdss/

beagle$ cd /sys/devices/platform/omapdss/
beagle$ ls -F
display0@  manager1/                     overlay0/  subsystem@
display1@  microamps_requested_vdda_dac  overlay1/  uevent
driver@    microamps_requested_vdds_dsi  overlay2/
manager0/  modalias                      power/
beagle$ cd overlay0
beagle$ ls -F
enabled       input_size  name         position
global_alpha  manager     output_size  screen_width
beagle$ cat position
beagle$ cat manager
beagle$ cat output_size

Investigate mplayer

Load Big Buck Bunny. This took some 3 minutes for me.

beagle$ cd exercises/gstreamer
beagle$ git clone git://github.com/MarkAYoder/esc-media.git
beagle$ cd esc-media

Now, start Big Buck Bunny and discover how it uses DSS

beagle$ mplayer BigBuckBunny_640x360.m4v
beagle$ cd /sys/devices/platform/omapdss
beagle$ ls
beagle$ cd overlay0
beagle$ cat enabled

Repeat for overlay1 and 2, Which are being used? cd to it.

Play with scale and position

beagle$ cd /sys/devices/platform/omapdss/overlay2
beagle$ cat position
beagle$ echo 100,100 >  position
beagle$ cat output_size
beagle$ echo 320,400 > output_size

Try transparency

beagle$ echo 127 > global_alpha
beagle$ cd ../manager0
beagle$ echo 1 > alpha_blending_enabled
beagle$ echo 1 > trans_key_enabled
beagle$ echo 65535 > trans_key_value

Caution: You may have to disable an overlay before changing some values.

beagle$ echo “0” > $ovl0/enabled


Note what you have learned in a short memo.


Can you get mplayer to appear in two windows?

thumb‎ Embedded Linux Class by Mark A. Yoder