From 8257a3899a384a2984d5f1bde4f56815cfef5dba Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Mon, 3 Jan 2022 19:47:26 -0600
Subject: [PATCH] feat(ppu): implement VRAM

---
 src/bus.zig | 19 +++++++++++--------
 src/ppu.zig | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 8 deletions(-)
 create mode 100644 src/ppu.zig

diff --git a/src/bus.zig b/src/bus.zig
index c486c77..37b240a 100644
--- a/src/bus.zig
+++ b/src/bus.zig
@@ -3,18 +3,21 @@ const std = @import("std");
 const Io = @import("bus/io.zig").Io;
 const Bios = @import("bus/bios.zig").Bios;
 const GamePak = @import("bus/pak.zig").GamePak;
+const Ppu = @import("ppu.zig").Ppu;
+
 const Allocator = std.mem.Allocator;
 
 pub const Bus = struct {
     pak: GamePak,
     bios: Bios,
+    ppu: Ppu,
     io: Io,
 
     pub fn init(alloc: Allocator, path: []const u8) !@This() {
         return @This(){
             .pak = try GamePak.init(alloc, path),
-            // TODO: don't hardcode this + bundle open-sorce Boot ROM
-            .bios = try Bios.init(alloc, "./bin/gba_bios.bin"),
+            .bios = try Bios.init(alloc, "./bin/gba_bios.bin"), // TODO: don't hardcode this + bundle open-sorce Boot ROM
+            .ppu = try Ppu.init(alloc),
             .io = Io.init(),
         };
     }
@@ -29,7 +32,7 @@ pub const Bus = struct {
 
             // Internal Display Memory
             0x0500_0000...0x0500_03FF => std.debug.panic("[Bus:32] read from 0x{X:} in BG/OBJ Palette RAM", .{addr}),
-            0x0600_0000...0x0601_7FFF => std.debug.panic("[Bus:32] read from 0x{X:} in VRAM", .{addr}),
+            0x0600_0000...0x0601_7FFF => self.ppu.vram.get32(@as(usize, addr - 0x0600_0000)),
             0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:32] read from 0x{X:} in OAM", .{addr}),
 
             // External Memory (Game Pak)
@@ -44,7 +47,7 @@ pub const Bus = struct {
         };
     }
 
-    pub fn write32(_: *@This(), addr: u32, word: u32) void {
+    pub fn write32(self: *@This(), addr: u32, word: u32) void {
         // TODO: write32 can write to GamePak Flash
 
         switch (addr) {
@@ -55,7 +58,7 @@ pub const Bus = struct {
 
             // Internal Display Memory
             0x0500_0000...0x0500_03FF => std.debug.panic("[Bus:32] wrote 0x{X:} to 0x{X:} in BG/OBJ Palette RAM", .{ word, addr }),
-            0x0600_0000...0x0601_7FFF => std.debug.panic("[Bus:32] wrote 0x{X:} to 0x{X:} in VRAM", .{ word, addr }),
+            0x0600_0000...0x0601_7FFF => self.ppu.vram.set32(@as(usize, addr - 0x0600_0000), word),
             0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:32] wrote 0x{X:} to 0x{X:} in OAM", .{ word, addr }),
 
             else => std.log.warn("[Bus:32] ZBA tried to write 0x{X:} to 0x{X:}", .{ word, addr }),
@@ -72,7 +75,7 @@ pub const Bus = struct {
 
             // Internal Display Memory
             0x0500_0000...0x0500_03FF => std.debug.panic("[Bus:16] read from 0x{X:} in BG/OBJ Palette RAM", .{addr}),
-            0x0600_0000...0x0601_7FFF => std.debug.panic("[Bus:16] read from 0x{X:} in VRAM", .{addr}),
+            0x0600_0000...0x0601_7FFF => self.ppu.vram.get16(@as(usize, addr - 0x0600_0000)),
             0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:16] read from 0x{X:} in OAM", .{addr}),
 
             // External Memory (Game Pak)
@@ -98,7 +101,7 @@ pub const Bus = struct {
 
             // Internal Display Memory
             0x0500_0000...0x0500_03FF => std.debug.panic("[Bus:16] write 0x{X:} to 0x{X:} in BG/OBJ Palette RAM", .{ halfword, addr }),
-            0x0600_0000...0x0601_7FFF => std.debug.panic("[Bus:16] write 0x{X:} to 0x{X:} in VRAM", .{ halfword, addr }),
+            0x0600_0000...0x0601_7FFF => self.ppu.vram.set16(@as(usize, addr - 0x0600_0000), halfword),
             0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:16] write 0x{X:} to 0x{X:} in OAM", .{ halfword, addr }),
 
             else => std.log.warn("[Bus:16] ZBA tried to write 0x{X:} to 0x{X:}", .{ halfword, addr }),
@@ -115,7 +118,7 @@ pub const Bus = struct {
 
             // Internal Display Memory
             0x0500_0000...0x0500_03FF => std.debug.panic("[Bus:8] read from 0x{X:} in BG/OBJ Palette RAM", .{addr}),
-            0x0600_0000...0x0601_7FFF => std.debug.panic("[Bus:8] read from 0x{X:} in VRAM", .{addr}),
+            0x0600_0000...0x0601_7FFF => self.ppu.vram.get8(@as(usize, addr - 0x0600_0000)),
             0x0700_0000...0x0700_03FF => std.debug.panic("[Bus:8] read from 0x{X:} in OAM", .{addr}),
 
             // External Memory (Game Pak)
diff --git a/src/ppu.zig b/src/ppu.zig
new file mode 100644
index 0000000..387db69
--- /dev/null
+++ b/src/ppu.zig
@@ -0,0 +1,47 @@
+const std = @import("std");
+
+const Allocator = std.mem.Allocator;
+
+pub const Ppu = struct {
+    vram: Vram,
+
+    pub fn init(alloc: Allocator) !@This() {
+        return @This(){
+            .vram = try Vram.init(alloc),
+        };
+    }
+};
+
+const Vram = struct {
+    buf: []u8,
+
+    fn init(alloc: Allocator) !@This() {
+        return @This(){
+            .buf = try alloc.alloc(u8, 0x18000),
+        };
+    }
+
+    pub inline fn get32(self: *const @This(), 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 inline fn set32(self: *@This(), 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 inline fn get16(self: *const @This(), idx: usize) u16 {
+        return (@as(u16, self.buf[idx + 1]) << 8) | @as(u16, self.buf[idx]);
+    }
+
+    pub inline fn set16(self: *@This(), idx: usize, halfword: u16) void {
+        self.buf[idx + 1] = @truncate(u8, halfword >> 8);
+        self.buf[idx] = @truncate(u8, halfword);
+    }
+
+    pub inline fn get8(self: *const @This(), idx: usize) u8 {
+        return self.buf[idx];
+    }
+};