[Bug 1086] White pixel "noise" corrupts display dynamically after some boots

bugzilla-daemon at bugzilla.openmoko.org bugzilla-daemon at bugzilla.openmoko.org
Mon Dec 10 08:47:45 CET 2007


------- Additional Comments From andy at openmoko.com  2007-12-10 08:47 -------
Before we got to try the patch I experienced the problem here.  I noticed that 
when it is corrupting pixels, there is a "hum bar" kind of effect vertically 
which somehow alters the colours of pixels in vertical ranks slowly, over a 
couple of seconds in a vertical sweep.  The pixels are rewritten behind 
this "wave front" so the display is still pretty legible.

I also noticed some kind of interlace or interleave is visible making the 
pixels "twinkle" where they differ between the two lines.

I wondered immediately if the problem was a slow pixel clock, and the "hum 
bar" in that case was the capacitive decay of the TFT gate level over time.  
Sure enough when Willie got a 'scope, we measured PCLK in the bad mode and 
afterwards in the good mode: ~1.7MHz vs ~24.5MHz or ~15 times slower when it 
is bad.  So it seems likely this is to do with PLL settings or issue with wait 
for lock.

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