Difference between revisions of "BackLight"

Revision as of 11:10, 17 November 2008

This page will explain you how to configure and use the Linux driver controlling the BackLight of your LCD

Introduction

Backlight control is done through the i.MXL integrated BackLight PWM. The output signal of this PWM is redirected to the BACKLIGHT pin of your LCD connector.
In short the driver is mainly exporting a /sys interface to user space, allowing you to change the Duty Cycle of the PWM output signal and so the backlight intensity of the LCD.

Installation

$ make linux-menuconfig

• in Device Drivers ---> Graphics support ---> Backlight & LCD device support, select <M> Lowlevel Backlight controls
• in Device Drivers ---> Armadeus specific drivers ---> Support for specific Armadeus drivers, select <M> i.MXL backLight driver
• If built in kernel, reflash your kernel image; if selected as module either reflash your rootfs or copy backlight.ko, imx_bl.ko and .../lib/modules/2.6.18.1/modules.dep to your target (for more infos: Linux_drivers_generalities). Then on your APF:

# modprobe imx_bl
i.MX Backlight driver initialized.

Usage

All backlight controls are done through the /sys interface:

# ls /sys/class/backlight/imxl-bl/

actual_brightness  max_brightness     subsystem
brightness         power              uevent

• To see the actual brightness:

# cat /sys/class/backlight/imxl-bl/actual_brightness

• To see the max allowed brightness:

# cat /sys/class/backlight/imxl-bl/max_brightness

• To change the brightness:

# echo 100 > /sys/class/backlight/imxl-bl/brightness

There is a small test script in target/linux/modules/backlight/test/

Links

• How a PWM is working
• http://www.armadeus.com/wiki/index.php?title=FrameBuffer#Tips