On 26.06.2005, you wrote:
> On 6/26/05, Linus Nielsen Feltzing <firstname.lastname@example.org> wrote:
>> BlueChip wrote:
>> Backlight fading on the archos was done a looooooooooooong
>> time ago. By Amiconn, iirc.
>> ...but never committed, because it put too much strain on the
>> CPU and I2C, IIRC.
> I take this as a no for my initial question :-)
Unfortunately it's not possible for mainstream rockbox, however,
the reason is *not* the cpu load.
Recently I did some more experiments to evaluate that kind of
stuff. There are 3 types of backlight and backlight circuitry
used in the various archoses:
(1) The Ondio family: These are prepared for backlight, but so
far we know of no single unmodded Ondio equipped with a
backlight. This backlight, if installed by a hardware mod,
is controlled by an I/O port pin, but since it is an EL
backlight, it's not dimmable. The EL driver chip would need
special features to allow this.
(2) The Recorder family: These have a LED backlight which in
theory is dimmable by PWM. However, the backlight is not
directly connected to a CPU port pin, but to a port pin of
the RTC. That means this port is only controllable via the
I2C bus, which should not be done in interrupts, and doing
it from a thread does not allow for precise enough timing.
I have an experimental plugin that dims the recorder
backlight nicely, but as soon as something else accesses
the I2C bus, like playing music which requires controlling
the MAS, the unit will lock up sooner or later.
(3) The player family: These have a LED backlight with is
hooked up to a CPU port pin, so it should be dimmable the
same way as the iriver backlight is. I actually tried it,
but it does not work. Instead of nicely fading, it just
flickers a bit, then goes off. There seems to be additional
circuitry between the port pin and the LEDs that prevents
It was not the code's fault; I tried dimming the red LED
instead which worked like a charm.
So unfortunately, no backlight dimming possible on archos :-(
Received on Sun Jun 26 22:32:20 2005