[Oberon] RGB display in Oberon RISC5

[Tomas Kral]

Hi Magnus,

That is all perfect, we now have 3 bit VGA, and also 4 bit VGA with
colour map support. That is plenty to play around with colours.

I am just thinking, if there could be yet another approach? As in
PO.System chapter 4.5. p52, it describes:

".. it is assumed, that all cells hosting B/W monitors are allocated to
the left of all cells hosting colour monitors". 

In the picture it shows 1st, 2nd and 3rd cell. With the 3rd keeping the
colour attributes.

Many thanks so far.


-- 
Tomas Kral <thomas.kral at email.cz>

On Wed, 2016-04-20 at 09:03 -0700, Magnus Karlsson wrote:
> It would be trivial to modify the code to add a fixed 16-entry lookup
> table for the output color based on the 4-bit pixel value (just a case
> statement).  However, due to differences in the native color
> capabilities of the different hardware platforms capable of running
> Oberon RISC5 (Digilent Spartan3 board has 3-bit color, OberonStation
> has 6-bit color, Pepino has 8-bit color and Pipistrello has 24-bit
> color) the implementation of the lookup table table would be slightly
> different.  The 3-bit color output that I did is supported by all
> platforms.  
> 
> Also, if you want the lookup table to be dynamic instead of fixed
> (i.e. CPU read/write access to the table) then that would add a bit of
> extra complexity but still very doable.  
> 
> BTW, my initial goal of the RGB version of VID.v was to implement a
> RGB video system with as few changes as possible, mostly for
> educational purpose since the question was asked in this mailing list
> as to how such modifications could be done.  Making the pixel size a
> power-of-2 value minimizes both the hardware changes and software
> changes at the expense of wasted memory space. 
> 
> Magnus
> 
> 
> On 4/19/2016 12:12 AM, Jörg Straube wrote:
> 
> > Hi Magnus
> > 
> > Thx for preparing VID.v
> > As the original ProjectOberon has only 1M of memory, it's a pity to waste 25% of your 4 bit color layout. Basically, we could use 16 colors instead of 8.
> > Instead of mapping the bits directly to RGB, I would rather use the 4 bits as index into a color palette.
> > 
> > Display.Mod has to be adapted accordingly.
> > 
> > Jörg
> > 
> > > Am 18.04.2016 um 21:59 schrieb Magnus Karlsson <magnus at saanlima.com>:
> > > 
> > > I have made an updated version of VID.v with support for an RGB video buffer.
> > > 
> > > The video buffer is now 4x larger (about 40% of the total 1 MB RAM) and video refresh will use up about 40% of the memory bandwidth.
> > > 
> > > See http://saanlima.com/forum/viewtopic.php?f=14&p=1786#p1783 for Verilog code and bit files for Pepino_LX9 and Pepino_LX25.
> > > 
> > > Magnus
> > > --
> > > Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
> > > https://lists.inf.ethz.ch/mailman/listinfo/oberon
> > > 
> > > 
> > > --
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> > > https://lists.inf.ethz.ch/mailman/listinfo/oberon
> 
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