Hrrm...I dug up Thin Red Line and realized that even it
has the same problem as my later code...if I change the
background color to non-black, I see a black line at the
top.
Looking at Rodrigo's "Thin Blue Rod" routine
(yeesh, sounds like a porn flick)...he doesn't have
this issue. But he's doing line counting, rather than
the timer. (Incidentally, Rodrigo, I think most people use the
timer instead of counting lines because that way they don't
need to make sure that all their calculations during vblank
fit into scanlinesized chunks)
Just for a lark, I decided to mess around with the timer...
it turns out if I put 45 or 46 into TIM64T the main line
goes away, though there is still a small line underneath it.
But making the timer wait for more doesn't make intuitive
sense to me...anyone know what's going on?
Here's the code. CHange the #43 to #46 to see the effect
I'm talking about...
; thin red line by Kirk Israel
processor 6502
include vcs.h
org $F000
Start
SEI
CLD
LDX #$FF
TXS
LDA #0
ClearMem
STA 0,X
DEX
BNE ClearMem
LDA #$99
STA COLUBK
LDA #33
STA COLUP0
MainLoop
LDA #2
STA VSYNC
STA WSYNC
STA WSYNC
STA WSYNC
LDA #43
STA TIM64T
LDA #0
STA VSYNC
WaitForVblankEnd
LDA INTIM
BNE WaitForVblankEnd
LDY #191
STA VBLANK
LDA #$F0
STA HMM0
STA WSYNC
STA HMOVE
ScanLoop
STA WSYNC
LDA #2
STA ENAM0
DEY
BNE ScanLoop
LDA #2
STA WSYNC
STA VBLANK
LDX #30
OverScanWait
STA WSYNC
DEX
BNE OverScanWait
JMP MainLoop
org $FFFC
.word Start
.word Start
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