src/bus/io.zig

@@ -14,7 +14,7 @@ pub const Io = struct {
     ie: InterruptEnable,
     irq: InterruptRequest,
     postflg: PostFlag,
-    haltcnt: HaltControl,
+    is_halted: bool,
 
     keyinput: KeyInput,
 
@@ -23,9 +23,9 @@ pub const Io = struct {
             .ime = false,
             .ie = .{ .raw = 0x0000 },
             .irq = .{ .raw = 0x0000 },
+            .postflg = .{ .raw = 0x00 },
             .keyinput = .{ .raw = 0x03FF },
-            .postflg = .FirstBoot,
-            .haltcnt = .Execute,
+            .is_halted = false,
         };
     }
 };
@@ -33,9 +33,9 @@ pub const Io = struct {
 pub fn read32(bus: *const Bus, addr: u32) u32 {
     return switch (addr) {
         0x0400_0000 => bus.ppu.dispcnt.raw,
-        0x0400_0004 => @as(u32, bus.ppu.vcount.raw) << 16 | bus.ppu.dispstat.raw,
-        0x0400_0006 => @as(u32, bus.ppu.bg[0].cnt.raw) << 16 | bus.ppu.vcount.raw,
-        0x0400_0200 => @as(u32, bus.io.irq.raw) << 16 | bus.io.ie.raw,
+        0x0400_0004 => bus.ppu.dispstat.raw,
+        0x0400_0006 => bus.ppu.vcount.raw,
+        0x0400_0200 => bus.io.ie.raw,
         0x0400_0208 => @boolToInt(bus.io.ime),
         0x0400_00C4 => failed_read("Tried to read word from DMA1CNT", .{}),
         0x0400_00D0 => failed_read("Tried to read word from DMA2CNT", .{}),
@@ -78,10 +78,7 @@ pub fn write32(bus: *Bus, addr: u32, word: u32) void {
         0x0400_00C0 => log.warn("Wrote 0x{X:0>8} to DMA1DAD", .{word}),
         0x0400_00C8 => log.warn("Wrote 0x{X:0>8} to DMA2SAD", .{word}),
         0x0400_00CC => log.warn("Wrote 0x{X:0>8} to DMA2DAD", .{word}),
-        0x0400_0200 => {
-            bus.io.ie.raw = @truncate(u16, word);
-            bus.io.irq.raw &= ~@truncate(u16, word >> 16);
-        },
+        0x0400_0200 => bus.io.ie.raw = @truncate(u16, word),
         0x0400_0204 => log.warn("Wrote 0x{X:0>8} to WAITCNT", .{word}),
         0x0400_0208 => bus.io.ime = word & 1 == 1,
         else => std.debug.panic("Tried to write 0x{X:0>8} to 0x{X:0>8}", .{ word, addr }),
@@ -95,7 +92,6 @@ pub fn read16(bus: *const Bus, addr: u32) u16 {
         0x0400_0006 => bus.ppu.vcount.raw,
         0x0400_0130 => bus.io.keyinput.raw,
         0x0400_0200 => bus.io.ie.raw,
-        0x0400_0202 => bus.io.irq.raw,
         0x0400_0208 => @boolToInt(bus.io.ime),
         0x0400_0102 => failed_read("Tried to read halfword from TM0CNT_H", .{}),
         0x0400_0106 => failed_read("Tried to read halfword from TM1CNT_H", .{}),
@@ -110,10 +106,7 @@ pub fn write16(bus: *Bus, addr: u32, halfword: u16) void {
     switch (addr) {
         0x0400_0000 => bus.ppu.dispcnt.raw = halfword,
         0x0400_0004 => bus.ppu.dispstat.raw = halfword,
-        0x0400_0008 => bus.ppu.bg[0].cnt.raw = halfword,
-        0x0400_000A => bus.ppu.bg[1].cnt.raw = halfword,
-        0x0400_000C => bus.ppu.bg[2].cnt.raw = halfword,
-        0x0400_000E => bus.ppu.bg[3].cnt.raw = halfword,
+        0x0400_0008...0x0400_000F => bus.ppu.bg[addr & 0x3].cnt.raw = halfword,
         0x0400_0010 => bus.ppu.bg[0].hofs.raw = halfword, // TODO: Don't write out every HOFS / VOFS?
         0x0400_0012 => bus.ppu.bg[0].vofs.raw = halfword,
         0x0400_0014 => bus.ppu.bg[1].hofs.raw = halfword,
@@ -169,7 +162,7 @@ pub fn read8(bus: *const Bus, addr: u32) u8 {
         0x0400_0000 => @truncate(u8, bus.ppu.dispcnt.raw),
         0x0400_0004 => @truncate(u8, bus.ppu.dispstat.raw),
         0x0400_0200 => @truncate(u8, bus.io.ie.raw),
-        0x0400_0300 => @enumToInt(bus.io.postflg),
+        0x0400_0300 => bus.io.postflg.raw,
         0x0400_0006 => @truncate(u8, bus.ppu.vcount.raw),
         0x0400_0089 => failed_read("Tried to read (high) byte from SOUNDBIAS", .{}),
         else => std.debug.panic("Tried to read byte from 0x{X:0>8}", .{addr}),
@@ -178,10 +171,8 @@ pub fn read8(bus: *const Bus, addr: u32) u8 {
 
 pub fn write8(self: *Bus, addr: u32, byte: u8) void {
     switch (addr) {
-        0x0400_0004 => self.ppu.dispstat.raw = (self.ppu.dispstat.raw & 0xFF00) | byte,
-        0x0400_0005 => self.ppu.dispstat.raw = (@as(u16, byte) << 8) | (self.ppu.dispstat.raw & 0xFF),
         0x0400_0208 => self.io.ime = byte & 1 == 1,
-        0x0400_0301 => self.io.haltcnt = if (byte >> 7 & 1 == 0) .Halt else std.debug.panic("TODO: Implement STOP", .{}),
+        0x0400_0301 => self.io.is_halted = byte >> 7 & 1 == 0, // TODO: Implement Stop?
         0x0400_0063 => log.warn("Tried to write 0x{X:0>2} to SOUND1CNT_H (high)", .{byte}),
         0x0400_0065 => log.warn("Tried to write 0x{X:0>2} to SOUND1CNT_X (high)", .{byte}),
         0x0400_0069 => log.warn("Tried to write 0x{X:0>2} to SOUND2CNT_L (high)", .{byte}),
@@ -201,16 +192,10 @@ fn failed_read(comptime format: []const u8, args: anytype) u8 {
 }
 
 /// Read / Write 
-pub const PostFlag = enum(u1) {
-    FirstBoot = 0,
-    FurtherBoots = 1,
-};
-
-/// Write Only
-pub const HaltControl = enum {
-    Halt,
-    Stop,
-    Execute,
+pub const PostFlag = extern union {
+    /// 0 if First Boot, 1 if a Reset has been done
+    not_first_boot: Bit(u8, 0),
+    raw: u8,
 };
 
 /// Read / Write

src/cpu.zig

@@ -247,7 +247,7 @@ pub const Arm7tdmi = struct {
 
     pub fn step(self: *Self) u64 {
         // If we're halted, the cpu is disabled
-        if (self.bus.io.haltcnt == .Halt) return 1;
+        if (self.bus.io.is_halted) return 1;
 
         if (self.cpsr.t.read()) {
             const opcode = self.thumbFetch();
@@ -270,7 +270,7 @@ pub const Arm7tdmi = struct {
         const should_handle = self.bus.io.ie.raw & self.bus.io.irq.raw;
 
         if (should_handle != 0) {
-            self.bus.io.haltcnt = .Execute;
+            self.bus.io.is_halted = false;
             // log.info("An Interrupt was Fired!", .{});
 
             // Either IME is not true or I in CPSR is true