[FE training-materials-updates] Android labs: ask the trainees to fix the backlight

Alexandre Belloni alexandre.belloni at free-electrons.com
Tue Feb 4 09:18:39 CET 2014

Repository : git://git.free-electrons.com/training-materials.git

On branch  : master
Link       : http://git.free-electrons.com/training-materials/commit/?id=d7d2cadf574f25f995e29b61b0afecdb34cd39c9


commit d7d2cadf574f25f995e29b61b0afecdb34cd39c9
Author: Alexandre Belloni <alexandre.belloni at free-electrons.com>
Date:   Tue Feb 4 00:05:08 2014 +0100

    Android labs: ask the trainees to fix the backlight
    Signed-off-by: Alexandre Belloni <alexandre.belloni at free-electrons.com>


 labs/android-new-board/android-new-board.tex |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/labs/android-new-board/android-new-board.tex b/labs/android-new-board/android-new-board.tex
index 85b4c95..4f4d78c 100644
--- a/labs/android-new-board/android-new-board.tex
+++ b/labs/android-new-board/android-new-board.tex
@@ -362,3 +362,21 @@ Once there's extraction's done, you can reboot the board. On the
 serial port, you should see Android going through its boot process,
 until you finally have a shell on the serial link and the screen
 working properly.
+\section{Fix the blank screen}
+After the android logo, the screen will turn black. This is actually
+the backlight turning almost off.
+You can find the controls for the backlight in
+\code{/sys/class/backlight} and as this is controlled by a PWM some
+other controls are available in \code{/sys/class/pwm}. Play with those
+controls until you find the values that are working.
+To make those changes permanently, you will have to edit the kernel
+code. The used PWM is defined is the \code{am335xevm} board file, in
+the \code{arch/arm/mach-omap2} folder.
+Once you're done, rebuild the kernel, boot it, and you should be able
+to read the screen now!

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