From: Manuel Dejonghe <limbus_at_gmail.com>
Date: Mon, 27 Jun 2005 03:17:22 +0200

Wow, thanks Jens for that extensive explanation.

I already presumed (1), deducted (2) from Linus' post that you had to
do TWI, err, I mean I²C for that, but your explanation shows me that
rockbox helps me a lot to learn electronics.
For (3): Lately I've seen transistors going off too slow that resulted
in the same effect. Publicity: It was on the following hardware
(german page with a lot of images):
http://koeln.ccc.de/prozesse/running/fnordlicht/

->bed, Manuel

On 6/26/05, Jens Arnold <arnold-j_at_t-online.de> wrote:
> Hello Manuel
>
> On 26.06.2005, you wrote:
>
> > On 6/26/05, Linus Nielsen Feltzing <linus_at_haxx.se> 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
> nice dimming.
> 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 :-(
>
>
> Regards, Jens
>

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Received on 2005-06-27