From 9d1229fe0cdd26c0a3dcd983a082c3d9916fbd60 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Fri, 21 Oct 2022 05:11:49 -0300
Subject: [PATCH] feat: implement PPU Timings in Scheduler

---
 src/bus/io.zig    | 15 +++++++++++----
 src/ppu.zig       |  4 ++++
 src/scheduler.zig | 47 ++++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 59 insertions(+), 7 deletions(-)

diff --git a/src/bus/io.zig b/src/bus/io.zig
index 54044e9..b20bbbc 100644
--- a/src/bus/io.zig
+++ b/src/bus/io.zig
@@ -5,13 +5,15 @@ const Bitfield = bitfield.Bitfield;
 const Bit = bitfield.Bit;
 
 pub const Io = struct {
-    dispcnt: Dispcnt,
-    dispstat: Dispstat,
+    dispcnt: DispCnt,
+    dispstat: DispStat,
+    vcount: VCount,
 
     pub fn init() @This() {
         return .{
             .dispcnt = .{ .raw = 0x0000_0000 },
             .dispstat = .{ .raw = 0x0000_0000 },
+            .vcount = .{ .raw = 0x0000_0000 },
         };
     }
 
@@ -48,7 +50,7 @@ pub const Io = struct {
     }
 };
 
-const Dispcnt = extern union {
+const DispCnt = extern union {
     bg_mode: Bitfield(u16, 0, 3),
     frame_select: Bit(u16, 4),
     hblank_interraw_free: Bit(u16, 5),
@@ -61,7 +63,7 @@ const Dispcnt = extern union {
     raw: u16,
 };
 
-const Dispstat = extern union {
+const DispStat = extern union {
     vblank: Bit(u16, 0),
     hblank: Bit(u16, 1),
     vcount: Bit(u16, 2),
@@ -71,3 +73,8 @@ const Dispstat = extern union {
     vcount_setting: Bitfield(u16, 8, 7),
     raw: u16,
 };
+
+const VCount = extern union {
+    scanline: Bitfield(u16, 0, 8),
+    raw: u16,
+};
diff --git a/src/ppu.zig b/src/ppu.zig
index fcd85c1..c841779 100644
--- a/src/ppu.zig
+++ b/src/ppu.zig
@@ -2,6 +2,7 @@ const std = @import("std");
 
 const Allocator = std.mem.Allocator;
 const Scheduler = @import("scheduler.zig").Scheduler;
+const EventKind = @import("scheduler.zig").EventKind;
 
 pub const Ppu = struct {
     vram: Vram,
@@ -9,6 +10,9 @@ pub const Ppu = struct {
     sched: *Scheduler,
 
     pub fn init(alloc: Allocator, sched: *Scheduler) !@This() {
+        // Queue first Hblank
+        sched.push(.{ .kind = .HBlank, .tick = sched.tick + 240 * 4 });
+
         return @This(){
             .vram = try Vram.init(alloc),
             .palette = try Palette.init(alloc),
diff --git a/src/scheduler.zig b/src/scheduler.zig
index fc4d38c..58d16d3 100644
--- a/src/scheduler.zig
+++ b/src/scheduler.zig
@@ -25,7 +25,7 @@ pub const Scheduler = struct {
         self.queue.deinit();
     }
 
-    pub fn handleEvent(self: *@This(), _: *Arm7tdmi, _: *Bus) void {
+    pub fn handleEvent(self: *@This(), _: *Arm7tdmi, bus: *Bus) void {
         const should_handle = if (self.queue.peek()) |e| self.tick >= e.tick else false;
 
         if (should_handle) {
@@ -36,15 +36,55 @@ pub const Scheduler = struct {
                     std.debug.panic("[Scheduler] Somehow, a u64 overflowed", .{});
                 },
                 .HBlank => {
-                    std.debug.panic("[Scheduler] tick {}: Hblank", .{self.tick});
+                    std.log.debug("[Scheduler] tick {}: Hblank", .{self.tick});
+
+                    // We've reached the end of a scanline
+                    const scanline = bus.io.vcount.scanline.read();
+                    bus.io.vcount.scanline.write(scanline + 1);
+
+                    bus.io.dispstat.hblank.set();
+
+                    if (scanline < 160) {
+                        self.push(.{ .kind = .Visible, .tick = self.tick + (68 * 4) });
+                    } else {
+                        self.push(.{ .kind = .VBlank, .tick = self.tick + (68 * 4) });
+                    }
+                },
+                .Visible => {
+                    std.log.debug("[Scheduler] tick {}: Visible", .{self.tick});
+
+                    // Beginning of a Scanline
+                    bus.io.dispstat.hblank.unset();
+                    bus.io.dispstat.vblank.unset();
+
+                    self.push(.{ .kind = .HBlank, .tick = self.tick + (240 * 4) });
                 },
                 .VBlank => {
-                    std.debug.panic("[Scheduler] tick {}: VBlank", .{self.tick});
+                    std.log.debug("[Scheduler] tick {}: VBlank", .{self.tick});
+
+                    // Beginning of a Scanline, not visible though
+                    bus.io.dispstat.hblank.unset();
+                    bus.io.dispstat.vblank.set();
+
+                    const scanline = bus.io.vcount.scanline.read();
+                    bus.io.vcount.scanline.write(scanline + 1);
+
+                    if (scanline < 227) {
+                        // Another Vblank Scanline
+                        self.push(.{ .kind = .VBlank, .tick = self.tick + 68 * (308 * 4) });
+                    } else {
+                        bus.io.vcount.scanline.write(0); // Reset Scanline
+                        self.push(.{ .kind = .Visible, .tick = self.tick + 68 * (308 * 4) });
+                    }
                 },
             }
         }
     }
 
+    pub inline fn push(self: *@This(), event: Event) void {
+        self.queue.add(event) catch unreachable;
+    }
+
     pub inline fn nextTimestamp(self: *@This()) u64 {
         if (self.queue.peek()) |e| {
             return e.tick;
@@ -65,4 +105,5 @@ pub const EventKind = enum {
     HeatDeath,
     HBlank,
     VBlank,
+    Visible,
 };