From bfdad9fa320091c2a4c238668e95979f1cfbb013 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Fri, 21 Oct 2022 05:12:19 -0300
Subject: [PATCH] feat: implement OAM

---
 src/Bus.zig | 10 +++++-----
 src/ppu.zig | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/src/Bus.zig b/src/Bus.zig
index 07524ad..ec3ec77 100644
--- a/src/Bus.zig
+++ b/src/Bus.zig
@@ -49,7 +49,7 @@ pub fn read32(self: *const Self, addr: u32) u32 {
         // Internal Display Memory
         0x0500_0000...0x0500_03FF => self.ppu.palette.get32(addr - 0x0500_0000),
         0x0600_0000...0x0601_7FFF => self.ppu.vram.get32(addr - 0x0600_0000),
-        0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:32] read from 0x{X:} in OAM", .{addr}),
+        0x0700_0000...0x0700_03FF => self.ppu.oam.get32(addr - 0x0700_0000),
 
         // External Memory (Game Pak)
         0x0800_0000...0x09FF_FFFF => self.pak.get32(addr - 0x0800_0000),
@@ -75,7 +75,7 @@ pub fn write32(self: *Self, addr: u32, word: u32) void {
         // Internal Display Memory
         0x0500_0000...0x0500_03FF => self.ppu.palette.set32(addr - 0x0500_0000, word),
         0x0600_0000...0x0601_7FFF => self.ppu.vram.set32(addr - 0x0600_0000, word),
-        0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:32] wrote 0x{X:} to 0x{X:} in OAM", .{ word, addr }),
+        0x0700_0000...0x0700_03FF => self.ppu.oam.set32(addr - 0x0700_0000, word),
 
         else => log.warn("32-bit write of 0x{X:0>8} to 0x{X:0>8}", .{ word, addr }),
     }
@@ -92,7 +92,7 @@ pub fn read16(self: *const Self, addr: u32) u16 {
         // Internal Display Memory
         0x0500_0000...0x0500_03FF => self.ppu.palette.get16(addr - 0x0500_0000),
         0x0600_0000...0x0601_7FFF => self.ppu.vram.get16(addr - 0x0600_0000),
-        0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:16] read from 0x{X:} in OAM", .{addr}),
+        0x0700_0000...0x0700_03FF => self.ppu.oam.get16(addr - 0x0700_0000),
 
         // External Memory (Game Pak)
         0x0800_0000...0x09FF_FFFF => self.pak.get16(addr - 0x0800_0000),
@@ -117,7 +117,7 @@ pub fn write16(self: *Self, addr: u32, halfword: u16) void {
         // Internal Display Memory
         0x0500_0000...0x0500_03FF => self.ppu.palette.set16(addr - 0x0500_0000, halfword),
         0x0600_0000...0x0601_7FFF => self.ppu.vram.set16(addr - 0x0600_0000, halfword),
-        0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:16] write 0x{X:} to 0x{X:} in OAM", .{ halfword, addr }),
+        0x0700_0000...0x0700_03FF => self.ppu.oam.set16(addr - 0x0700_0000, halfword),
 
         else => log.warn("16-bit write of 0x{X:0>4} to 0x{X:0>8}", .{ halfword, addr }),
     }
@@ -134,7 +134,7 @@ pub fn read8(self: *const Self, addr: u32) u8 {
         // Internal Display Memory
         0x0500_0000...0x0500_03FF => self.ppu.palette.get8(addr - 0x0500_0000),
         0x0600_0000...0x0601_7FFF => self.ppu.vram.get8(addr - 0x0600_0000),
-        0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:8] read from 0x{X:} in OAM", .{addr}),
+        0x0700_0000...0x0700_03FF => self.ppu.oam.get8(addr - 0x0700_0000),
 
         // External Memory (Game Pak)
         0x0800_0000...0x09FF_FFFF => self.pak.get8(addr - 0x0800_0000),
diff --git a/src/ppu.zig b/src/ppu.zig
index 865022e..c89d00f 100644
--- a/src/ppu.zig
+++ b/src/ppu.zig
@@ -14,6 +14,7 @@ pub const Ppu = struct {
 
     vram: Vram,
     palette: Palette,
+    oam: Oam,
     sched: *Scheduler,
     framebuf: []u8,
     alloc: Allocator,
@@ -28,6 +29,7 @@ pub const Ppu = struct {
         return Self{
             .vram = try Vram.init(alloc),
             .palette = try Palette.init(alloc),
+            .oam = try Oam.init(alloc),
             .sched = sched,
             .framebuf = framebuf,
             .alloc = alloc,
@@ -158,3 +160,44 @@ const Vram = struct {
         return self.buf[idx];
     }
 };
+
+const Oam = struct {
+    const Self = @This();
+
+    buf: []u8,
+    alloc: Allocator,
+
+    fn init(alloc: Allocator) !Self {
+        const buf = try alloc.alloc(u8, 0x400);
+        std.mem.set(u8, buf, 0);
+
+        return Self{
+            .buf = buf,
+            .alloc = alloc,
+        };
+    }
+
+    pub fn get32(self: *const Self, idx: usize) u32 {
+        return (@as(u32, self.buf[idx + 3]) << 24) | (@as(u32, self.buf[idx + 2]) << 16) | (@as(u32, self.buf[idx + 1]) << 8) | (@as(u32, self.buf[idx]));
+    }
+
+    pub fn set32(self: *Self, idx: usize, word: u32) void {
+        self.buf[idx + 3] = @truncate(u8, word >> 24);
+        self.buf[idx + 2] = @truncate(u8, word >> 16);
+        self.buf[idx + 1] = @truncate(u8, word >> 8);
+        self.buf[idx] = @truncate(u8, word);
+    }
+
+    pub fn get16(self: *const Self, idx: usize) u16 {
+        return (@as(u16, self.buf[idx + 1]) << 8) | @as(u16, self.buf[idx]);
+    }
+
+    pub fn set16(self: *Self, idx: usize, halfword: u16) void {
+        self.buf[idx + 1] = @truncate(u8, halfword >> 8);
+        self.buf[idx] = @truncate(u8, halfword);
+    }
+
+    pub fn get8(self: *const Self, idx: usize) u8 {
+        return self.buf[idx];
+    }
+};