Backlight (PWM)

Hello,

is it possible to make the backlight dimmable by hardware pwm port (I think
its GPB1) on the mini2440 board? And how must I configure it right in the
kernel source (mach-mini2440.c)?

I have already tried to set GPB1 as S3C2410_GPB1_TOUT1 and setting the PWM
duty but it hasn't worked yet. In a manual for this board it says that GPB1
can be used for modulated LCD power. Only GPG4 is working for me but this
port hasn't any hardware PWM controller so I would have to use software PWM
and thats not optimal. I use the default NEC35 as display with the On-Board
controller.

Also I have another problem that the backlight turns off a few seconds
after loading the kernel so I have to enable it later in userspace again.
How can I figure that out?

Just must change some resistors;
http://www.friendlyarm.net/forum/topic/401

Hmmm...
In the post it says that R12 must be removed and R13 must be installed on
the adaptor board. But there already is an R13 on it!

Jay, those instructions are for the A70 display. It doesn't look like your
display connects the PWM pin to anything on the display. Sorry.

Its a little bit tricky with software PWM (you don't need a hardware pwm
port to do this!) but finally I got it:

type in serial console for half brightness (depends on the kernel you use
but its working for me):
echo timer > /sys/class/leds/backlight/trigger
echo 5 > /sys/class/leds/backlight/delay_off
echo 5 > /sys/class/leds/backlight/delay_on

And my backlight is at half brightness!

A little bit darker (but flickering a little bit):
echo timer > /sys/class/leds/backlight/trigger
echo 6 > /sys/class/leds/backlight/delay_off
echo 2 > /sys/class/leds/backlight/delay_on

Have fun to experiment with this :)

There isn't much more system load using this.

Hello Jay,

can you post some delay_off and delay_on settings which will give a nick
backlight (and hence good screen contrast) ?? thanks!

Dear,

Maybe the subject is quite old, but I've read this :

"The PWM output (GPB1 can be configured by register as PWM) and reset
signal (nRESET) are led out for the convenience of testing. The LCD_PWR is
the back light controlling signal."
See
http://resources.mini-box.com/online/MBD-mini2440+7in-LCD/MBD-mini2440+7...

"The LED backlight can be turned on or off or modulated with GPB1. The
backlight signal is called LCD_PWR PWM output (GPB1 be sent through
Depositors configuration for
PWM), and reset signals (nRESET), one of backlight control signals are
LCD_PWR."
See
http://www.andahammer.com/assets/Uploads/All2440/Firmware/Mini2440Essent...

I have not understood everything as GPB1 can be pwm, so a modulated signal.
So what's the use of LCD_PWR wich is said to be a backlight control signal?

Regards