[Server-devel] turn off backlight on XS-on-XO1

[James Cameron]

On Tue, Mar 02, 2010 at 09:00:50PM -0600, Anna wrote:
> I'd appreciate a command to blank the screen.

Your subject line mentions the backlight, and blanking the screen is
potentially a different task.

I've tested an XO-1 with build 802b1.

If you mean the backlight, you can manually control this from a shell
command or program like this:

echo 0 > /sys/class/backlight/dcon-bl/brightness

or

echo 0 > /sys/devices/platform/dcon/backlight/dcon-bl/brightness

Change the 0 to 15 for full brightness.  With the backlight off, the
screen image should still be visible.

You can manually turn off the screen and hide the screen image with this
shell command:

echo 1 > /sys/devices/platform/dcon/sleep

But it doesn't turn back on automatically.  You can appear to lose
control this way; you can restore it to normal with this:

echo 0 > /sys/devices/platform/dcon/sleep

The text console does idle blank after a while, though without turning
off the backlight.

It is possible to initiate screen blanking manually using code that
calls ioctl with TIOCLINUX and TIOCL_BLANKSCREEN but like the idle
console blanking it leaves square brackets on screen.  The other three
modes of VESA blanking that the kernel can do (TIOCL_SETVESABLANK) don't
fare any better than the default.  Two of the modes do the bit rot melt down
effect on the display.

It is also possible to manipulate the blanking timers using escape
sequences sent to /dev/tty1 ... but again, we haven't integrated the
VESA blanking feature of the kernel with our DCON and backlight.

-- 
James Cameron
http://quozl.linux.org.au/