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fix(ppu): delay ppu by one cycle on scx fifo discard
continuous-integration/drone/push Build is passing Details

This commit is contained in:
Rekai Nyangadzayi Musuka 2021-07-16 21:01:30 -05:00
parent cc0cb0dd8a
commit 1d8fb8d32a
1 changed files with 18 additions and 5 deletions
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23
src/ppu.rs
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@ -51,6 +51,10 @@ pub struct Ppu {
obj_buffer: ObjectBuffer, obj_buffer: ObjectBuffer,
frame_buf: Box<[u8; GB_WIDTH * GB_HEIGHT * 4]>, frame_buf: Box<[u8; GB_WIDTH * GB_HEIGHT * 4]>,
window_stat: WindowStatus, window_stat: WindowStatus,
scanline_start: bool,
to_discard: u8,
x_pos: u8, x_pos: u8,
cycle: Cycle, cycle: Cycle,
} }
@ -105,6 +109,8 @@ impl Ppu {
} }
self.x_pos = 0; self.x_pos = 0;
self.scanline_start = true;
self.to_discard = 0;
self.fetch.hblank_reset(); self.fetch.hblank_reset();
self.window_stat.hblank_reset(); self.window_stat.hblank_reset();
@ -375,12 +381,17 @@ impl Ppu {
} }
if self.fifo.is_enabled() { if self.fifo.is_enabled() {
if self.x_pos == 0 && !self.fifo.back.is_empty() { if self.x_pos == 0 && !self.fifo.back.is_empty() && self.scanline_start {
let to_discard = self.pos.scroll_x % 8; self.to_discard = self.pos.scroll_x % 8;
self.scanline_start = false;
for _ in 0..to_discard {
let _ = self.fifo.back.pop_front();
} }
if self.to_discard > 0 {
let _ = self.fifo.back.pop_front();
self.to_discard -= 1;
// Delay the PPU by one cycle
return;
} }
// Handle Background Pixel and Sprite FIFO // Handle Background Pixel and Sprite FIFO
@ -472,6 +483,8 @@ impl Default for Ppu {
window_stat: Default::default(), window_stat: Default::default(),
dma: Default::default(), dma: Default::default(),
x_pos: 0, x_pos: 0,
scanline_start: true,
to_discard: Default::default(),
} }
} }
} }