Advantech RSB-4210 Evaluation Kit User Manual download pdf (Page 103)

95 RSB-4210 User Manual

Chapter 3 Software Functionality

More detail please reference "source/linux-2.6.35.4/Documentation/input/input.txt".

3.12 Backlight Adjustment

The brightness of the display backlight can be adjusted in a range from 0 to 255. The

value is exported as a virtual file in the sysfs under /sys/class/backlight/

pwm_backlight/brightness. It can be accessed using the standard file operations

open(), read(), write() and close().

Example 1: Reading and adjusting the current backlight brightness on the console

root #cat /sys/class/backlight/pwm-backlight/brightness

255

root # echo 100 > /sys/class/backlight/pwm-backlight/bright-

ness

root #cat /sys/class/backlight/pwm-backlight/brightness

100

Please note that this value is not persistent, i.e. it gets lost when the device is

rebooted. In order to change the brightness permanently, it has to be set in the XML

configuration, which is also mapped into the sysfs under /sys/class/misc/guf_xml/

configurationFile/variables/display/backlight/level_ac.

The PWM settings used allow the adjustment of the duty cycle in 255 steps.

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Advantech RSB-4210 Evaluation Kit User Manual Page 103