Re: [stella] DD Dead end?

Subject: Re: [stella] DD Dead end?
From: Thomas Jentzsch <tjentzsch@xxxxxx>
Date: Sat, 10 Nov 2001 20:14:27 +0100
Glenn Saunders wrote:
> At 11:11 AM 11/10/2001 +0100, you wrote:
>> could reduce the vertical resolution (not the positioning!) to two
>>pixels. Then you would need four (2x2) kernels, depending if your missiles
>>start at an odd or even line. That way you could reduce the missile
>>cycles down to 52, plus a few extra cycles (~6..10) because you have to
>>clear the HMMx registers.

> If you aren't going to reduce the vertical positioning then how do you get 
> both missiles to start on the same scanline?

As I said, you need four kernels:
1. both missiles start in the first row
2. missile 0 starts in first row, missile 1 in second row
3. missile 0 starts in second row, missile 1 in first row
4. both missiles start in the second row

> I think the problem with your math is that you aren't taking into account 
> the timing-critical playfield code.  The two little windows of time between 
> the playfield load/stores are very short.  I'll experiment a little and see 
> if I can wedge the sprite code in there.  I don't know what else I could 
> use that area for.  Right now each area is only 16 cycles long.

Well, you can reorganize your playfield writes:

    LDA     <PF1DataRAM-1,X   ; 4
    STA     PF1               ; 3     @27      (just in time :-)
    LDA     <PF2DataRAM-1,X   ; 4
    STA     PF2               ; 3     @34
    LDA     <PF1bDataRAM-1,X  ; 4
    STA     PF1               ; 3     @41
    LDA     <PF2bDataRAM-1,X  ; 4
    STA     PF2               ; 3     @48

That way you can move the cycles before the PF writes and merge them
with other cycles.

Have fun!
Thomas Jentzsch         | *** Every bit is sacred ! ***
tjentzsch at web dot de |

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