🚀 go-pugleaf

0. I took Spectrum apart with a logic analyzer one day.  This is not for the
   faint of heart:

1. Spectrum 512 is a kernel (any 2600 programmers out there?).

2. There is a clever synchronization technique.  Basically they use
   the video scan register (the low byte of it) to determine how far
   the processor is into the line, using it as a jump-index into a
   table of NOPs when it changes.  The number of NOPs is (are?) tuned
   so the 68000 starts off "on the right foot" of the kernel.

3. All interrupts are off (IPL-7) during the kernel, naturally.

4. Each line of the kernel itself looks something like:

	MOVEM.L	<location>,<register-mask>	; suck-in pallette assignments
	MOVEM.L	<register-mask>,COLOR0		; set pallette registers
	MOVEM.L	<location>,<register-mask>	; suck-in pallette assignments
	MOVEM.L	<register-mask>,COLOR0		; set pallette registers
	MOVEM.L	<location>,<register-mask>	; suck-in pallette assignments
	MOVEM.L	<register-mask>,COLOR0		; set pallette registers
	(NOPs for alignment)			; sync with next scanline

   Quiz: how many registers do you need?  How many cycles does this take?
   [Hint: you can get about 3.5 complete pallette changes on a scanline].

5. This gets you 48+ colors on a LINE.  I don't know how to get 48 CONSECUTIVE
   colors -- I suspect it is impossible without playing tricks with alternating
   video frames.  There may be other even more hair-raising things you can do
   with MOVEM, however.

-- 

I speak for me.