> It might be possible, that the TIA finishes it's setup routine already
> at cycle 22, since cycle 23 ends one pixel in the display.
>
> This would explain the stange gun position in Atlantis. The
> RESPx might end at cycle 22, which would be 2 pixels before
> display time. If we add the strange 5 pixel offset, the gun
> would be at pixel 3. The HMOVE of 3 pixels to the left, that
> you mentioned, would put the gun right at pixel 1.
I did a trace of Atlantis to see how it's positioning P0 for the gun
on the left side of the screen and here it is:
PC=160b IR=85 <$nn 2 0 STA > A=c0 X=ff Y= 8 PS=e5 SP=ff Cyc=14584
PC=160d IR=85 <$nn 10 0 STA > A=c0 X=ff Y= 8 PS=e5 SP=ff Cyc=14587
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y= 7 PS=65 SP=ff Cyc=14589
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y= 7 PS=65 SP=ff Cyc=14592
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y= 6 PS=65 SP=ff Cyc=14594
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y= 6 PS=65 SP=ff Cyc=14597
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y= 5 PS=65 SP=ff Cyc=14599
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y= 5 PS=65 SP=ff Cyc=14602
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y= 4 PS=65 SP=ff Cyc=14604
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y= 4 PS=65 SP=ff Cyc=14607
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y= 3 PS=65 SP=ff Cyc=14609
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y= 3 PS=65 SP=ff Cyc=14612
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y= 2 PS=65 SP=ff Cyc=14614
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y= 2 PS=65 SP=ff Cyc=14617
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y= 1 PS=65 SP=ff Cyc=14619
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y= 1 PS=65 SP=ff Cyc=14622
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y= 0 PS=67 SP=ff Cyc=14624
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y= 0 PS=67 SP=ff Cyc=14627
PC=160f IR=88 <implied 0 0 DEY > A=c0 X=ff Y=ff PS=e5 SP=ff Cyc=14629
PC=1610 IR=10 <implied 0 0 BPL > A=c0 X=ff Y=ff PS=e5 SP=ff Cyc=14631
PC=1612 IR=85 <$nn 11 0 STA > A=c0 X=ff Y=ff PS=e5 SP=ff Cyc=14634
PC=1614 IR=a9 <#$nn 1615 0 LDA > A= 0 X=ff Y=ff PS=67 SP=ff Cyc=14636
PC=1616 IR=85 <$nn 1d 0 STA > A= 0 X=ff Y=ff PS=67 SP=ff Cyc=14639
PC=1618 IR=85 <$nn 1e 0 STA > A= 0 X=ff Y=ff PS=67 SP=ff Cyc=14642
PC=161a IR=a9 <#$nn 161b 30 LDA > A=30 X=ff Y=ff PS=65 SP=ff Cyc=14644
PC=161c IR=85 <$nn 20 0 STA > A=30 X=ff Y=ff PS=65 SP=ff Cyc=14647
PC=161e IR=a9 <#$nn 161f 50 LDA > A=50 X=ff Y=ff PS=65 SP=ff Cyc=14649
PC=1620 IR=85 <$nn 21 0 STA > A=50 X=ff Y=ff PS=65 SP=ff Cyc=14652
PC=1622 IR=a5 <$nn 95 80 LDA > A=80 X=ff Y=ff PS=e5 SP=ff Cyc=14655
PC=1624 IR=85 <$nn 91 90 STA > A=80 X=ff Y=ff PS=e5 SP=ff Cyc=14658
PC=1626 IR=a5 <$nn 96 78 LDA > A=78 X=ff Y=ff PS=65 SP=ff Cyc=14661
PC=1628 IR=85 <$nn 93 80 STA > A=78 X=ff Y=ff PS=65 SP=ff Cyc=14664
PC=162a IR=85 <$nn 2 0 STA > A=78 X=ff Y=ff PS=65 SP=ff Cyc=14736
PC=162c IR=85 <$nn 2a 0 STA > A=78 X=ff Y=ff PS=65 SP=ff Cyc=14739
PC=162e IR=a0 <#$nn 162f 7 LDY > A=78 X=ff Y= 7 PS=65 SP=ff Cyc=14741
PC=1630 IR=ae <$nnnn 1e37 cb LDX > A=78 X=cb Y= 7 PS=e5 SP=ff Cyc=14745
PC=1633 IR=ad <$nnnn 1e27 3a LDA > A=3a X=cb Y= 7 PS=65 SP=ff Cyc=14749
PC=1636 IR=85 <$nn 2 0 STA > A=3a X=cb Y= 7 PS=65 SP=ff Cyc=14812
The only things that looks strange to me is that the RESP0 occurs
right after a write to WSYNC. The HMOVE occurs after a write to WSYNC
as a good game should :-) And like I was saying HMP0 = $30 so it moves
the player 3 pixels to the left at the STA HMOVE.
Well I guess I better write some 2600 code to play with some of these
interesting effects.
Brad
P.S. I'm not writing these traces by hand they're generated by Stella using
a compile time option (they get very large after a few frames :-)
--------------------------------------------------------------------------
Bradford W. Mott (bwmott@xxxxxxx) Computer Science Department
http://www4.ncsu.edu/~bwmott/www North Carolina State University
--------------------------------------------------------------------------
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