chore: refactor GBA Display Timings

This change should reflect that the Hblank bit of DISPSTAT is toggled on all scanlines
while also ensuring that the Vblank bit is set on all Vblank scanlines

src/main.zig

@@ -16,6 +16,7 @@ const gba_height = @import("ppu.zig").height;
 const buf_pitch = @import("ppu.zig").buf_pitch;
 
 pub const enable_logging: bool = false;
+const is_binary: bool = false;
 
 pub fn main() anyerror!void {
     // Allocator for Emulator + CLI
@@ -48,7 +49,6 @@ pub fn main() anyerror!void {
     cpu.fastBoot();
 
     if (enable_logging) {
-        const is_binary: bool = true;
         const file_name = if (is_binary) "zba.bin" else "zba.log";
 
         const file = try std.fs.cwd().createFile(file_name, .{ .read = true });

src/scheduler.zig

@@ -36,26 +36,26 @@ pub const Scheduler = struct {
                     std.debug.panic("[Scheduler] Somehow, a u64 overflowed", .{});
                 },
                 .HBlank => {
-                    // The End of a Hblank
-                    const scanline = bus.io.vcount.scanline.read();
-                    const new_scanline = scanline + 1;
+                    // The End of a Hblank (During Draw or Vblank)
+                    const old_scanline = bus.io.vcount.scanline.read();
+                    const scanline = (old_scanline + 1) % 228;
 
-                    // TODO: Should this be done @ end of Draw instead of end of Hblank?
-                    bus.ppu.drawScanline(&bus.io);
+                    bus.io.vcount.scanline.write(scanline);
+                    bus.io.dispstat.hblank.unset();
 
-                    bus.io.vcount.scanline.write(new_scanline);
-
-                    if (new_scanline < 160) {
+                    if (scanline < 160) {
                         // Transitioning to another Draw
                         self.push(.Draw, self.tick + (240 * 4));
                     } else {
                         // Transitioning to a Vblank
-                        bus.io.dispstat.vblank.set();
-                        self.push(.VBlank, self.tick + (308 * 4));
+                        if (scanline < 227) bus.io.dispstat.vblank.set() else bus.io.dispstat.vblank.unset();
+
+                        self.push(.VBlank, self.tick + (240 * 4));
                     }
                 },
                 .Draw => {
                     // The end of a Draw
+                    bus.ppu.drawScanline(&bus.io);
 
                     // Transitioning to a Hblank
                     bus.io.dispstat.hblank.set();
@@ -63,23 +63,7 @@ pub const Scheduler = struct {
                 },
                 .VBlank => {
                     // The end of a Vblank
-
-                    const scanline = bus.io.vcount.scanline.read();
-                    const new_scanline = scanline + 1;
-                    bus.io.vcount.scanline.write(new_scanline);
-
-                    if (new_scanline == 227) bus.io.dispstat.vblank.unset();
-
-                    if (new_scanline < 228) {
-                        // Transition to another Vblank
-                        self.push(.VBlank, self.tick + (308 * 4));
-                    } else {
-                        // Transition to another Draw
-                        bus.io.vcount.scanline.write(0); // Reset Scanline
-
-                        // DISPSTAT was disabled on scanline 227
-                        self.push(.Draw, self.tick + (240 * 4));
-                    }
+                    self.push(.HBlank, self.tick + (68 * 4));
                 },
             }
         }