Fwd: LCM flicker

[Wolfgang Spraul]

fyi

Begin forwarded message:

> From: Andy Green <andy at openmoko.com>
> Date: March 9, 2008 6:50:31 PM GMT+08:00
> To: "Carsten Haitzler (The Rasterman)" <raster at openmoko.org>
> Cc: Wolfgang Spraul <wolfgang at openmoko.com>,  Sean Moss-Pultz <sean at openmoko.com 
> >, William Lai <will at openmoko.com>, "Tony Tu)" <tony at openmoko.com>,   
> matt_hsu <matt_hsu at openmoko.org>, Chia-I Wu <olv at openmoko.com>,  
> Werner Almesberger <werner at openmoko.org>
> Subject: Re: LCM flicker
>
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> Somebody in the thread at some point said:
>
>>> hhmmm. then xrandr is lying to me, it claims 50hz. aqnd it claims  
>>> 25hz for
>>> landscape mode (which explains the much worse flicker).
>
> It is true that landscape is 1/2 the rate of portrait currently, but  
> 680
> x 600 (the overscanned y and x) at 24.5MHz PCLK (41ns period) comes  
> out
> to 16.6ms == 60Hz.
>
>> Either the refresh action we perform "beats" against another  
>> oscialltor
>> inside the LCM ("booster" or this "internal" osciallator), or there  
>> is
>> some kind of PWM trickery used to get the intensity levels that we  
>> beat
>> against somehow.
>>
>>> i haven't found a pathological pattern yet - but it seems a smooth  
>>> gradient - in
>>> ANY direction seems to bring it out. that doesn't help me figure  
>>> out what kind
>>> of pathological pattern is causing it. for that matter a solid  
>>> orange color
>>> region flickers too - all by itself. no gradient needed.
>>
>>> rgb: 255 145 0 does a wonder flickering job. this is totally  
>>> bizarre unles u
>>> look at there being some temporal interference pattern on the r &  
>>> b signals
>>> that doesn't affect g, and the interference pattern is inverted  
>>> between r & b.
>
> Hum well it is a big clue for sure since we can make the problem come
> and go depending on colour.  I guess the first question we should  
> ask is
> can the glamo being doing it really early in the actual pixel data  
> frame
> by frame.  I will try to fill the display with this colour and have  
> a look.
>
> Another thing I noticed is that we have an insane RC filter on PCLK
> currently, the signal quality on PCLK is pretty bad.  But I can't  
> make a
> story how that causes these outcomes.
>
> - -Andy
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