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[Lcdproc] Please test: hd44780 backlight update

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  • From: bsdfan at (Markus Dolze)
  • Subject: [Lcdproc] Please test: hd44780 backlight update
  • Date: Sun, 25 Jan 2009 12:49:33 +0100


After analyzing Sascha's problem with 40x4 winamp-wired display I had a
closer look how the backlight is used.

I found that:

1. In render.c the backlight state is determined.
2. drivers.c passed the BL state to all drivers, if supported
3. The hd44780 passed the BL to the connection type, if supported
4. The conntection type sets the hardware accordingly.

Besides a possible problem in 3. because the hardware is asked to set
the backlight off if the user specified no backlight being available in
the config file, the whole chain is executed with every screen rendering.

Looking at how other drivers handle this I found some implement an
"incremental" backlight change (only update hardware if the the state
has really changed) while others do not.

I decided to implement this "incremental update" for the hd44780 driver
as well. Patch attached.

As this applies to all connection types, I ask developers and users with
hd44780 type displays and backlight to test the impact of this change. I
already tested with lcd2usb and winamp (but without switchable
backlight) and found no problems so far.

Please also test what happens if "Backlight=off" is set in LCDd.conf.

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  • [Lcdproc] Please test: hd44780 backlight update, Markus Dolze, 01/25/2009

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