Subject: Re: qtopia
To: Garrett D'Amore <>
From: David Laight <>
List: tech-kern
Date: 06/05/2006 21:48:23
On Sat, Jun 03, 2006 at 09:23:40PM -0700, Garrett D'Amore wrote:
> > As for TFTs, I was under the
> > impression that the analog refresh rate doesn't matter because the
> > internal analog->digital panel converter has no glow decay like a CRT
> > (same goes for the refresh rate of a panel connected via DVI btw).
> This is true.  Most panels prefer to run at 60Hz.  Driving them faster
> serves no purpose, AFAIK can actually be detrimental (increased power
> consumption and wear?)

Actually many VGA connected LCD panels will not work at > 60Hz at their
preferred resolution, the AD converter just isn't up to it.

I've also (in the past) done some experiments with the pixel clock speed
on directly connected LCD panels (connected to an SA1101).  In order to
reduce display flicker we had to run the pixel clock at the absolute
maximum value, unfortunately this caused underruns whenever the system
did a 'slow' memory access (or more likely back to back slow cycles) [1].

Slowing the pixel clock right down showed the cause of the flicker - about
1" (probably 32 lines?) of the display were drawn black before being
refreshed to the 'correct' colour.  This requires a refresh rate that
approaches that of CRTs to avoid flicker.
There was also a slight colour difference between alternate frames.


[1] solved by dynamically changing the pixel clock across accress to
pcmcia space and cache-line reads from the EEPROM.

David Laight: