Re: [Linux-fbdev-devel] Advice sought on approach.

[Antonino D. <ad...@po...>]

On Wed, 2003-03-05 at 20:37, Alex Bennee wrote:
> Hi,
> 
> I'm writting a framebuffer driver for an embedded system that has a
> overlayed video display (TV picture + Overlayed text). To do this I have
> to keep track of both the main pixel memory and a mask that the hardware
> uses to display things. This is also compilcated by the fact I can't
> access this memory directly, it is done through a small addr/data port
> on the hardware so obviosuly I want to minimise the amount of data I
> push through this (by doing it only when required).
> 
> Having read the fb-dev docs on www.linux-fbdev.org I'm a little confused
> as to what actually puts data into the framebuffer. Most of the
> framebuffer drivers just seem to deal with resolution and colourmap
> settings. Is this a case of having to re-implement the fbcon drivers as
> well to get what I want?
> 

The pixels placed to the framebuffer are all done in the fbcon-cfb*.c
modules (if you use the generic functions).  This is for standard
character drawing.  The logo is drawn indepently (fbcon_show_logo in
fbcon.c).  User applications write directly to the framebuffer via the
mmap() function.

> Are there any examples of drivers that have a similar architecture that
> would be worth looking at? I've had a look at the vfb.c code but again
> that seems too simplistic compared to what I'll need.

Search the archives for SED1335.  The author implemented a shadowed
virtual framebuffer using system memory.  The contents of the virtual
framebuffer are written to the data port periodically via a timer
function.

> 
> Final question, the docs refer to 2.2. Is this because under 2.4
> framebuffer drivers are not fundamentally differnt?

Yes.

Tony