QVGA for Neo

Harald Welte laforge at openmoko.org
Thu Oct 4 15:20:22 CEST 2007

Hi, sorry for my delayed response. 

On Thu, Sep 27, 2007 at 06:42:47AM -0700, john cass wrote:
> I have been playing with QVGA mode for the Neo and have some observations and 
> questions. QVGA will be important for several key Neo applications including 
> games and movie playing.  It may also offer lower power usage.

yes, we've always wanted QVGA support, but with all the higher priority

> The LCM register set is not documented but a patch was made by Stefan Schmidt 
> which demonstrated switching it into QVGA mode.(patch for /drivers/spi/jbt6k74.c)
> Basically this patch changes two register values called DISPLAY_MODE and 
> QUAD_RATE, it also fills in timing values to an alternate set of registers 
> for vga or qvga.
> This patch does not change the framebuffer driver (within the s3c2410 - 
> /drivers/video/s3c2410fb.c) which by default is set up to always generate a 
> VGA signal.

I thought Stefan was never able to finish his QVGA patch ?!?

Anyway, what a pleasant surprise.

In QVGA mode, the LCM needs the following minimal timings:

vertical cycle 		326	line
vertical data start	  4	line
verical sync pulse	  2	line
vertical front porch	  2 	line
vertical back porch	  2	line
vertical blanking period  6	line
vertical active area	320	line
horizontal cycle	344	dot
horizontal front porch	 88	dot
horizontal fsync pulse	  8	dot
horizontal back porch	  8	dot
horizontal data start	 16	dot
horizontal active area	240	dot
clock frequency		6.5	MHz

So once the LCM has been switched to QVGA using jbt6k74, the s3c2410_fb
needs to be re-programmed to generate a signal according to the
abovementioned specs.
> 1) Does qvga mode in the LCM require/expect a vga signal, or can it run from a 
>     qvga signal?  

QVGA signal accordign to specs above.

>     As it stands, we can see qvga on the screen but linux (console, X)  still 
>     thinks it has a 480x640 framebuffer (which it does!) and I cant see a way 
>     of forcing it to use only a part of that.
>     It is relatively straightforward to change the framebuffer (and console, X) to
>     generate a qvga signal using fbset but will the LCM accept that?


happy hacking!
- Harald Welte <laforge at openmoko.org>          	        http://openmoko.org/
Software for the world's first truly open Free Software mobile phone

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