feat: implement Oam buffer

src/core/nds9/Bus.zig

@@ -82,6 +82,7 @@ fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T
         0x0400_0000...0x04FF_FFFF => io.read(self, T, aligned_addr),
         0x0500_0000...0x05FF_FFFF => readInt(T, self.makeshift_palram[aligned_addr & (2 * KiB - 1) ..][0..@sizeOf(T)]),
         0x0600_0000...0x06FF_FFFF => self.ppu.vram.read(T, .nds9, aligned_addr),
+        0x0700_0000...0x07FF_FFFF => readInt(T, self.ppu.oam.buf[aligned_addr..][0..byte_count]),
         0xFFFF_0000...0xFFFF_FFFF => self.bios.read(T, address),
         else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
     };
@@ -108,11 +109,12 @@ fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, v
     }
 
     switch (aligned_addr) {
-        0x0200_0000...0x02FF_FFFF => writeInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count], value),
+        0x0200_0000...0x02FF_FFFF => writeInt(T, self.main[aligned_addr & (4 * MiB - 1) ..][0..byte_count], value),
         0x0300_0000...0x03FF_FFFF => self.wram.write(T, .nds9, aligned_addr, value),
         0x0400_0000...0x04FF_FFFF => io.write(self, T, aligned_addr, value),
         0x0500_0000...0x05FF_FFFF => writeInt(T, self.makeshift_palram[aligned_addr & (2 * KiB - 1) ..][0..@sizeOf(T)], value),
         0x0600_0000...0x06FF_FFFF => self.ppu.vram.write(T, .nds9, aligned_addr, value),
+        0x0700_0000...0x07FF_FFFF => writeInt(T, self.ppu.oam.buf[aligned_addr & (2 * KiB - 1) ..][0..@sizeOf(T)], value),
         0xFFFF_0000...0xFFFF_FFFF => self.bios.write(T, address, value),
         else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
     }

src/core/nds9/io.zig

@@ -77,6 +77,8 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
         },
         u16 => switch (address) {
+            0x0400_0006 => bus.ppu.io.nds9.vcount.raw,
+
             // DMA Transfers
             0x0400_00B0...0x0400_00DE => dma.read(T, &bus.dma, address) orelse 0x0000,
             0x0400_00E0...0x0400_00EE => std.mem.readIntLittle(T, bus.io.dma_fill[address & 0xF ..][0..@sizeOf(T)]),
@@ -131,6 +133,14 @@ const subset = @import("../../util.zig").subset;
 pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
     switch (T) {
         u32 => switch (address) {
+            0x0400_0008 => {
+                bus.ppu.engines[0].bg[0].cnt.raw = @truncate(value >> 0); // 0x0400_0008
+                bus.ppu.engines[0].bg[1].cnt.raw = @truncate(value >> 16); // 0x0400_000A
+            },
+            0x0400_000C => {
+                bus.ppu.engines[0].bg[2].cnt.raw = @truncate(value >> 0); // 0x0400_000A
+                bus.ppu.engines[0].bg[3].cnt.raw = @truncate(value >> 16); // 0x0400_000C
+            },
 
             // DMA Transfers
             0x0400_00B0...0x0400_00DC => dma.write(T, &bus.dma, address, value),
@@ -155,6 +165,16 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_0210 => bus.io.ie.raw = value,
             0x0400_0214 => bus.io.irq.raw &= ~value,
 
+            0x0400_0244 => {
+                bus.ppu.vram.io.cnt_e.raw = @truncate(value >> 0); // 0x0400_0244
+                bus.ppu.vram.io.cnt_f.raw = @truncate(value >> 8); // 0x0400_0245
+                bus.ppu.vram.io.cnt_g.raw = @truncate(value >> 16); // 0x0400_0246
+                bus.io.shr.wramcnt.raw = @truncate(value >> 24); // 0x0400_0247
+
+                bus.ppu.vram.update();
+                bus.wram.update(bus.io.shr.wramcnt);
+            },
+
             0x0400_0290, 0x0400_0294 => {
                 bus.io.div.numerator = subset(u64, u32, address, bus.io.div.numerator, value);
                 bus.io.div.schedule(bus.scheduler);

src/core/ppu.zig

@@ -5,6 +5,8 @@ const Scheduler = @import("Scheduler.zig");
 const System = @import("emu.zig").System;
 
 const Vram = @import("ppu/Vram.zig");
+const Oam = @import("ppu/Oam.zig");
+
 const EngineA = @import("ppu/engine.zig").EngineA;
 const EngineB = @import("ppu/engine.zig").EngineB;
 
@@ -24,6 +26,9 @@ pub const Ppu = struct {
 
     vram: *Vram,
 
+    // FIXME: do I need a pointer here?
+    oam: *Oam,
+
     engines: struct { EngineA, EngineB },
 
     io: Io = .{},
@@ -49,12 +54,19 @@ pub const Ppu = struct {
             .fb = try FrameBuffer.init(allocator),
             .engines = .{ try EngineA.init(allocator), try EngineB.init(allocator) },
             .vram = vram,
+            .oam = blk: {
+                var oam = try allocator.create(Oam);
+                oam.init();
+
+                break :blk oam;
+            },
         };
     }
 
     pub fn deinit(self: @This(), allocator: Allocator) void {
         self.fb.deinit(allocator);
         inline for (self.engines) |eng| eng.deinit(allocator);
+        allocator.destroy(self.oam);
     }
 
     pub fn drawScanline(self: *@This(), bus: *System.Bus9) void {

src/core/ppu/Oam.zig

@@ -0,0 +1,7 @@
+const KiB = 0x400;
+
+buf: [2 * KiB]u8,
+
+pub fn init(self: *@This()) void {
+    @memset(self.buf[0..], 0);
+}