enquiry about 4 bpp frame buffer with nibbles swapped

[Aitor Garcia <carrierphasejitter@yahoo.com>]

Hi all,

I am trying to design a 4 bpp FB driver for iMX1 using
imxfb.c code as 
an starting point.
The problem that I have found is that MX1 video memory
is organised as
follows:

b7 b6 b5 b4  --> pixel 0.
b3 b2 b1 b0  --> pixel 1.

The software that I'm using to display things (Qtopia
Core) assumes a 
different scheme of memory to pixel mapping:

b7 b6 b5 b4 ---> pixel 1.
b3 b2 b1 b0 ---> pixel 0.

The solution to overcome this problem is apparently
easy:

#define SWAP_NIBBLES(in,out) (out=((in&0xf)<<4) |
((in&0xf0)>>4) |\
                                  ((in&0xf00)<<4) |
((in&0xf000)>>4) |\
		                  ((in&0xf0000)<<4) |
((in&0xf00000)>>4) |\
		                  ((in&0xf000000)<<4) |
((in&0xf0000000)>>4))

But I do not know where to do it. 
Frame Buffer has 3 functions cfb_fillrect,
cfb_copyarea and cfb_imageblit which I thought were
the key to solve my problems but Qtopia Core does not
make use
of them.  
imxfb_map_video_memory function or fb_mmap, seem to be
good candidates but I do not know how to progress
further.

I would be very grateful if I could receive some kind
of help.

Best wishes,

Aitor


 
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