color map vs. pseudo-palette vs. RAMDAC registers

[Rolf Offermanns <rolf.offermanns@gmx.net>]

Hi All,
I tried to understand the skeletonfb driver code, and I am confused by some 
comments in it:

I do not understand what the color map and pseudo palette stuff is used for.

From the c file:
--------------------------------------------------------------------
Pseudocolor:
* cmap is not used
* DAC[X] is programmed to (red, green, blue)
--------------------------------------------------------------------
Does that mean, I do not need to allocate a color map, if my driver would only 
support pseudocolor visual? Is pseudocolor always used for 8bpp or are there 
situations where 16bpp pseudocolor makes sense?

-----------------------------------------------------------------------------
Truecolor:
     *    does not use RAMDAC (usually has 3 of them).
     *    var->{color}.offset contains start of bitfield
     *    var->{color}.length contains length of bitfield
     *    cmap is programmed to (red << red.offset) | 
				(green << green.offset) |
    				(blue << blue.offset) | 
				(transp << transp.offset)
     *    RAMDAC does not exist
-----------------------------------------------------------------------------
Now I am lost:
-> does not use RAMDAC. 
I understand this. It states the same in my chip reference. But what means 
"usually has 3 of them" in this context?

-> cmap is programmed to...
In the code that follows this comment, not the cmap is programmed, but the 
pseudo palette.
1. Why do I need a pseudo palette and where does its size 16 comes from?
2. What do I need a color map for?

-> RAMDAC does not exist <-> "usually has 3 of them"
???

Please shed some light on me.

Thanks,
Rolf



-------------------------------------------------------
This SF.Net email is sponsored by the JBoss Inc.
Get Certified Today * Register for a JBoss Training Course
Free Certification Exam for All Training Attendees Through End of 2005
Visit http://www.jboss.com/services/certification for more information