[Oberon] FPGA - Display.Mod 4-bit colour

[Tomas Kral]

Hi,

I wish to modify `Display.Mod' to accept 4-bit colour. Standard
interface currently supports 1-bit colour only.

  PROCEDURE Dot*(col, x, y, mode: INTEGER);
  PROCEDURE ReplConst*(col, x, y, w, h, mode: INTEGER);
  PROCEDURE CopyPattern*(col, patadr, x, y, mode: INTEGER);
  PROCEDURE CopyBlock*(sx, sy, w, h, dx, dy, mode: INTEGER);
  PROCEDURE ReplPattern*(col, patadr, x, y, w, h, mode: INTEGER);

I have a version of VID.v with 4-bit pixels and a 16 entry colour
lookup table. So `col' parameter in the range {0..15} defines index
into that table.

Looking at the code, I realise each display line takes 128 bytes 1-bit.
4-bit it must be 4*128. While single word sets 1-bit colour of 32
pixels, and only 8 pixels of 4-bit colour, correct?

I am generally seeking advice for the good starting point, also hwoto
set up a test environment for quick tests turnaround? My idea was to
make a standalone boot program accepting draw commands over serial.

I may start with `ReplConst' (font rendering), and `ReplConst' (line
drawing).

I wonder how much of the original code I could reuse, just extending
the loop count, and some 4-bit manipulation?

Many thanks in advance.

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