difference in maximum color depth in Debian vs Mac OS?

[Fernan Aguero <fernan@iib.unsam.edu.ar>]

Hi!

I've had Debian woody (3.0r1) installed on my Power
Macintosh 7200/75 for a while. Over time, and after reading
different suggestions posted online, I've tried different
things to make X under Debian use a higher resolution and
color depth than the common (low) denominator of 640x480 @
256 colors.

I've provided kernel arguments in BootX
(platinumfb:vmode:13,cmode:16), and also played with
XF86Config-4.

I can make debian use a color depth of 16 at 640x480, and I
can also make debian use a resolution of 832x624, but at a
color depth of 8.

The Mac OS, OTOH can do 832x624 @ thousands of colors (16).

Recently I discovered fbset. I installed it and this is what
it reported for my system when run with no arguments:

mode "832x624-75"
    # D: 57.597 MHz, H: 49.997 kHz, V: 74.959 Hz
    geometry 832 624 832 624 8
    timings 17362 208 48 39 1 64 3
    rgba 8/0,8/0,8/0,0/0
endmode

After reading the man page I added this mode to
/etc/fb.modes (but without the line for "rgba") and
tried to now use fbset:

debian:~# fbset -fb /dev/fb0 -depth 16 "832x624-75"
platinum_var_to_par, not enough ram for vmode 13, cmode 1.
platinum_set_var: error calling platinum_var_to_par: -22.
ioctl FBIOPUT_VSCREENINFO: Invalid argument

So now, as before, I'm unable to swith to a higher color
depth at this resolution. But now at least I have an error
message. Is there any reason for this "not enough ram"?

The VRAM of this Macintosh is 1MB (expandable to 4MB I
believe). However what I fail to understand is why the Mac
OS is able to get a higher color depth than debian/linux on
the same hardware.


Thanks in advance for any suggestion. Are there other users
out there with similar problems?

Fernan