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| author | Miquel Sabaté Solà <mikisabate@gmail.com> | 2025-02-04 15:46:54 +0100 |
|---|---|---|
| committer | Miquel Sabaté Solà <mikisabate@gmail.com> | 2025-02-04 22:00:36 +0100 |
| commit | 3e7549c71f60ee1c4b49a7c09fde3b6017818089 (patch) | |
| tree | dc132aecc12b2ba2680edca912fa12778618ad02 /scroll | |
| parent | 6c4ac7727094259b3b5a25e8c168245983e70b2f (diff) | |
| download | code.nes-3e7549c71f60ee1c4b49a7c09fde3b6017818089.tar.gz code.nes-3e7549c71f60ee1c4b49a7c09fde3b6017818089.zip | |
Ensure background/sprite tiles are spread properly
At least on the MMC3 chip, it's important to have background tiles on
the first pattern table and then sprite tiles on the second pattern
table. This avoids a hardware bug on scanline IRQs.
Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
Diffstat (limited to 'scroll')
| -rw-r--r-- | scroll/roulette.s | 17 |
1 files changed, 7 insertions, 10 deletions
diff --git a/scroll/roulette.s b/scroll/roulette.s index ecf2569..4b13c22 100644 --- a/scroll/roulette.s +++ b/scroll/roulette.s @@ -1,6 +1,6 @@ ;;; ;; Divide the screen in three rows and make them move in different -;; directions/speed. This is achieved thanks to the MMC3 chip (check the +;; directions/speed. This is achieved thanks to the MMC3 chip (check ;; `fx/blink.s` for further information on this chip). In particular, we are ;; using the scanline IRQ mechanism provided by this chip to react to different ;; parts of the screen being rendered: @@ -208,7 +208,7 @@ reset: ;; NOTE: enable back interrupts so we can set them up later on `nmi` code. cli - lda #%10010000 + lda #%10001000 sta $2000 lda #%00011110 sta $2001 @@ -386,9 +386,9 @@ nmi: ldx #$00 stx MMC3::IRQ_DISABLE - ;; The screen is made up of 240 scan lines. Since we are dividing the screen - ;; by 3: 240 / 3 = 80. Hence, the next IRQ should happen on scanline 80, - ;; where we would need to update the scroll value through the + ;; The screen is made up of 240 visible scan lines. Since we are dividing + ;; the screen by 3: 240 / 3 = 80. Hence, the next IRQ should happen on + ;; scanline 80, where we would need to update the scroll value through the ;; `{center/bottom}_scroll` values instead. Moreover, note that ;; `MMC3::IRQ_ENABLE` accepts any value, so the same value as the two other ;; registers is just fine. @@ -493,15 +493,12 @@ irq: rti -;;; NOTE: pretty much the same as `fx/blink.s` but we also copy the same data on -;;; the second pattern table as that's the one being used for background -;;; elements. +;;; NOTE: pretty much the same as `fx/blink.s`. .segment "CHARS" .incbin "../assets/diskun0.chr" .incbin "../assets/diskun1.chr" -.incbin "../assets/diskun0.chr" -.incbin "../assets/diskun1.chr" +.res $1000, $00 ;; The 15 other 8KB portions are left empty. .res $2000, $00 |