DAC size with vesafb?

Hi there,

I am programming with Linux vesafb and below is my code which works for mobility radeon 7500 but does NOT work for GT 330M:

Code:

unsigned short R = (Pixel.R << 8);
unsigned short G = (Pixel.G << 8);
unsigned short B = (Pixel.B << 8);

fb_cmap Palette = {Index, 1, &R, &G, &B, NULL};

ioctl(Device, FBIOPUTCMAP, &Palette);

while below code works for GT 330M:

Code:

unsigned short R = (Pixel.R << 6);
unsigned short G = (Pixel.G << 6);
unsigned short B = (Pixel.B << 6);

fb_cmap Palette = {Index, 1, &R, &G, &B, NULL};

ioctl(Device, FBIOPUTCMAP, &Palette);

So my question is, how should I write my code to get the 6 or 8 during initialization? I have searched much on google but seems no luck.

Thanks in advance!

I suspect the issue is related to the video card's RAMDAC size (for standard VGA it's 6 bits for each color component, for some super VGA it's 8), but I could not have this size during code initialization.

It is possible to call interrupt 10h (AX = 4F00h) to query super VGA info and have the size, but this is not acceptable to me as my code is running in user space without root privilege.

I have also checked the info returned by FBIOGET_VSCREENINFO and FBIOGET_FSCREENINFO, but still no help.

Is it possible to make use of what's in /sys or some other (non-root) methods? Thanks for your help!

Is there anything in /usr/include/linux/fb.h which looks like it might be the thing?
It might help figure out which ioctl() returns the info you want.

Originally Posted by Salem

Is there anything in /usr/include/linux/fb.h which looks like it might be the thing?
It might help figure out which ioctl() returns the info you want.

Thanks for the reply, but I did not find anything interesting in /usr/include/linux/fb.h. Do you have some hints?