[Linux-fbdev-devel] Query:Regarding Virtual frame buffer

[Bipin T S <bi...@lg...>]

Hi,

>  We are using a Walnut board with a PPC processor. We don't have a
graphics chip/card in this board and so we planned to use the virtual
> frame buffer concept for debugging and testing the frame buffer
system. We build the kernel with the virtual frame buffer enabled in
Console
> drivers and we gave video = vfb:enable (Thanks to Simmons)  in the
command line options.

1) We tried giving echo "Hello World" > /dev/fb0. It works fine.

2) We wrote an application that mmaps the /dev/fb0 into user memory.
This works fine and mmap() returns a valid address

        fb = open("/dev/fb0", O_RDWR);
        addr =(unsigned char*)  mmap(NULL, size, PROT_READ|PROT_WRITE,
MAP_SHARED, fb, 0);

3) But when we try to write something into the MAPPED address, we get a
segmentation fault!!
            *( addr + 10) = 20;

We would like to know the reason for the above behaviour. Pointers and
references will be appreciated

Thanks and regards
Bipin