chore: document select unimplmented I/O registers

These registers are written to / read from Kirby: Nightmare in Dream Land

src/Bus.zig

@@ -138,7 +138,7 @@ pub fn read8(self: *const Self, addr: u32) u8 {
         0x0800_0000...0x09FF_FFFF => self.pak.get8(addr - 0x0800_0000),
         0x0A00_0000...0x0BFF_FFFF => self.pak.get8(addr - 0x0A00_0000),
         0x0C00_0000...0x0DFF_FFFF => self.pak.get8(addr - 0x0C00_0000),
-        0x0E00_0000...0x0E00_FFFF => std.debug.panic("Read from 0x{X:0>2} in Game Pak SRAM", .{addr}),
+        0x0E00_0000...0x0E00_FFFF => self.pak.sram.get8(addr - 0x0E00_0000),
 
         else => std.debug.panic("Tried to read from 0x{X:0>2}", .{addr}),
     };
@@ -153,7 +153,7 @@ pub fn write8(self: *Self, addr: u32, byte: u8) void {
         0x0400_0410 => log.info("Wrote 0x{X:0>2} to 0x{X:0>8}. Ignored", .{ byte, addr }),
 
         // External Memory (Game Pak)
-        0x0E00_0000...0x0E00_FFFF => log.err("Wrote 0x{X:0>2} to 0x{X:0>8} in Game Pak SRAM", .{ byte, addr }),
+        0x0E00_0000...0x0E00_FFFF => self.pak.sram.set8(addr - 0x0E00_0000, byte),
         else => std.debug.panic("Tried to write 0x{X:0>2} to 0x{X:0>8}", .{ byte, addr }),
     }
 }

src/bus/GamePak.zig

@@ -1,13 +1,14 @@
 const std = @import("std");
 
+const Sram = @import("Sram.zig");
 const Allocator = std.mem.Allocator;
+const log = std.log.scoped(.GamePak);
 const Self = @This();
 
 title: [12]u8,
 buf: []u8,
 alloc: Allocator,
-
-const log = std.log.scoped(.GamePak);
+sram: Sram,
 
 pub fn init(alloc: Allocator, path: []const u8) !Self {
     const file = try std.fs.cwd().openFile(path, .{});
@@ -17,7 +18,12 @@ pub fn init(alloc: Allocator, path: []const u8) !Self {
     const buf = try file.readToEndAlloc(alloc, len);
     const title = parseTitle(buf);
 
-    const pak = Self{ .buf = buf, .alloc = alloc, .title = title };
+    const pak = Self{
+        .buf = buf,
+        .alloc = alloc,
+        .title = title,
+        .sram = try Sram.init(alloc),
+    };
     pak.parseHeader();
 
     return pak;
@@ -49,6 +55,7 @@ fn lookupMaker(slice: *const [2]u8) ?[]const u8 {
 
 pub fn deinit(self: Self) void {
     self.alloc.free(self.buf);
+    self.sram.deinit();
 }
 
 pub fn get32(self: *const Self, idx: usize) u32 {

src/bus/Sram.zig

@@ -0,0 +1,31 @@
+const std = @import("std");
+
+const Allocator = std.mem.Allocator;
+const log = std.log.scoped(.SRAM);
+const Self = @This();
+
+buf: []u8,
+alloc: Allocator,
+
+pub fn init(alloc: Allocator) !Self {
+    // FIXME: SRAM is more than just a 64KB block of memory
+    const buf = try alloc.alloc(u8, 0x10000);
+    std.mem.set(u8, buf, 0);
+
+    return Self{
+        .buf = buf,
+        .alloc = alloc,
+    };
+}
+
+pub fn deinit(self: Self) void {
+    self.alloc.free(self.buf);
+}
+
+pub fn get8(self: *const Self, idx: usize) u8 {
+    return self.buf[idx];
+}
+
+pub fn set8(self: *Self, idx: usize, byte: u8) void {
+    self.buf[idx] = byte;
+}

src/bus/io.zig

@@ -37,7 +37,9 @@ pub fn read32(bus: *const Bus, addr: u32) u32 {
         0x0400_0006 => bus.ppu.vcount.raw,
         0x0400_0200 => bus.io.ie.raw,
         0x0400_0208 => @boolToInt(bus.io.ime),
-        else => std.debug.panic("Tried to read from {X:0>8}", .{addr}),
+        0x0400_00C4 => failed_read("Tried to read word from DMA1CNT", .{}),
+        0x0400_00D0 => failed_read("Tried to read word from DMA2CNT", .{}),
+        else => std.debug.panic("Tried to read word from 0x{X:0>8}", .{addr}),
     };
 }
 
@@ -72,6 +74,10 @@ pub fn write32(bus: *Bus, addr: u32, word: u32) void {
             bus.ppu.bg[3].hofs.raw = @truncate(u16, word);
             bus.ppu.bg[3].vofs.raw = @truncate(u16, word >> 16);
         },
+        0x0400_00BC => log.warn("Wrote 0x{X:0>8} to DMA1SAD", .{word}),
+        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),
         0x0400_0204 => log.warn("Wrote 0x{X:0>8} to WAITCNT", .{word}),
         0x0400_0208 => bus.io.ime = word & 1 == 1,
@@ -87,7 +93,12 @@ pub fn read16(bus: *const Bus, addr: u32) u16 {
         0x0400_0130 => bus.io.keyinput.raw,
         0x0400_0200 => bus.io.ie.raw,
         0x0400_0208 => @boolToInt(bus.io.ime),
-        else => std.debug.panic("Tried to read from {X:0>4}", .{addr}),
+        0x0400_0102 => failed_read("Tried to read halfword from TM0CNT_H", .{}),
+        0x0400_0106 => failed_read("Tried to read halfword from TM1CNT_H", .{}),
+        0x0400_010A => failed_read("Tried to read halfword from TM2CNT_H", .{}),
+        0x0400_010E => failed_read("Tried to read halfword from TM3CNT_H", .{}),
+        0x0400_0204 => failed_read("Tried to read halfword from WAITCNT", .{}),
+        else => std.debug.panic("Tried to read halfword from 0x{X:0>8}", .{addr}),
     };
 }
 
@@ -95,7 +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...0x0400_000F => bus.ppu.bg[addr & 0x7].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,
@@ -104,8 +115,43 @@ pub fn write16(bus: *Bus, addr: u32, halfword: u16) void {
         0x0400_001A => bus.ppu.bg[2].vofs.raw = halfword,
         0x0400_001C => bus.ppu.bg[3].hofs.raw = halfword,
         0x0400_001E => bus.ppu.bg[3].vofs.raw = halfword,
+        0x0400_0040 => log.warn("Wrote 0x{X:0>4} to WIN0H", .{halfword}),
+        0x0400_0042 => log.warn("Wrote 0x{X:0>4} to WIN1H", .{halfword}),
+        0x0400_0044 => log.warn("Wrote 0x{X:0>4} to WIN0V", .{halfword}),
+        0x0400_0046 => log.warn("Wrote 0x{X:0>4} to WIN1V", .{halfword}),
+        0x0400_0048 => log.warn("Wrote 0x{X:0>4} to WININ", .{halfword}),
+        0x0400_004A => log.warn("Wrote 0x{X:0>4} to WINOUT", .{halfword}),
+        0x0400_004C => log.warn("Wrote 0x{X:0>4} to MOSAIC", .{halfword}),
+        0x0400_0050 => log.warn("Wrote 0x{X:0>4} to BLDCNT", .{halfword}),
+        0x0400_0052 => log.warn("Wrote 0x{X:0>4} to BLDALPHA", .{halfword}),
+        0x0400_0054 => log.warn("Wrote 0x{X:0>4} to BLDY", .{halfword}),
+        0x0400_0080 => log.warn("Wrote 0x{X:0>4} to SOUNDCNT_L", .{halfword}),
+        0x0400_0082 => log.warn("Wrote 0x{X:0>4} to SOUNDCNT_H", .{halfword}),
+        0x0400_0084 => log.warn("Wrote 0x{X:0>4} to SOUNDCNT_X", .{halfword}),
+        0x0400_00BA => log.warn("Wrote 0x{X:0>4} to DMA0CNT_H", .{halfword}),
+        0x0400_00C6 => log.warn("Wrote 0x{X:0>4} to DMA1CNT_H", .{halfword}),
+        0x0400_00D2 => log.warn("Wrote 0x{X:0>4} to DMA2CNT_H", .{halfword}),
+        0x0400_00DE => log.warn("Wrote 0x{X:0>4} to DMA3CNT_H", .{halfword}),
+        0x0400_0100 => log.warn("Wrote 0x{X:0>4} to TM0CNT_L", .{halfword}),
+        0x0400_0102 => log.warn("Wrote 0x{X:0>4} to TM0CNT_H", .{halfword}),
+        0x0400_0104 => log.warn("Wrote 0x{X:0>4} to TM1CNT_L", .{halfword}),
+        0x0400_0106 => log.warn("Wrote 0x{X:0>4} to TM1CNT_H", .{halfword}),
+        0x0400_0108 => log.warn("Wrote 0x{X:0>4} to TM2CNT_L", .{halfword}),
+        0x0400_010A => log.warn("Wrote 0x{X:0>4} to TM2CNT_H", .{halfword}),
+        0x0400_010C => log.warn("Wrote 0x{X:0>4} to TM3CNT_L", .{halfword}),
+        0x0400_010E => log.warn("Wrote 0x{X:0>4} to TM3CNT_H", .{halfword}),
+        0x0400_0120 => log.warn("Wrote 0x{X:0>4} to SIOMULTI0", .{halfword}),
+        0x0400_0122 => log.warn("Wrote 0x{X:0>4} to SIOMULTI1", .{halfword}),
+        0x0400_0124 => log.warn("Wrote 0x{X:0>4} to SIOMULTI2", .{halfword}),
+        0x0400_0126 => log.warn("Wrote 0x{X:0>4} to SIOMULTI3", .{halfword}),
+        0x0400_0128 => log.warn("Wrote 0x{X:0>4} to SIOCNT", .{halfword}),
+        0x0400_012A => log.warn("Wrote 0x{X:0>4} to SIOMLT_SEND", .{halfword}),
+        0x0400_0130 => log.warn("Wrote 0x{X:0>4} to KEYINPUT. Ignored", .{halfword}),
+        0x0400_0132 => log.warn("Wrote 0x{X:0>4} to KEYCNT", .{halfword}),
+        0x0400_0134 => log.warn("Wrote 0x{X:0>4} to RCNT", .{halfword}),
         0x0400_0200 => bus.io.ie.raw = halfword,
         0x0400_0202 => bus.io.irq.raw &= ~halfword,
+        0x0400_0204 => log.warn("Wrote 0x{X:0>4} to WAITCNT", .{halfword}),
         0x0400_0208 => bus.io.ime = halfword & 1 == 1,
         else => std.debug.panic("Tried to write 0x{X:0>4} to 0x{X:0>8}", .{ halfword, addr }),
     }
@@ -118,7 +164,8 @@ pub fn read8(bus: *const Bus, addr: u32) u8 {
         0x0400_0200 => @truncate(u8, bus.io.ie.raw),
         0x0400_0300 => bus.io.postflg.raw,
         0x0400_0006 => @truncate(u8, bus.ppu.vcount.raw),
-        else => std.debug.panic("Tried to read from 0x{X:0>8}", .{addr}),
+        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}),
     };
 }
 
@@ -126,10 +173,24 @@ pub fn write8(self: *Bus, addr: u32, byte: u8) void {
     switch (addr) {
         0x0400_0208 => self.io.ime = byte & 1 == 1,
         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}),
+        0x0400_006D => log.warn("Tried to write 0x{X:0>2} to SOUND2CNT_H (high)", .{byte}),
+        0x0400_0070 => log.warn("Tried to write 0x{X:0>2} to SOUND3CNT_L (low)", .{byte}),
+        0x0400_0079 => log.warn("Tried to write 0x{X:0>2} to SOUND4CNT_L (high)", .{byte}),
+        0x0400_007D => log.warn("Tried to write 0x{X:0>2} to SOUND4CNT_H (high)", .{byte}),
+        0x0400_0080 => log.warn("Tried to write 0x{X:0>2} to SOUNDCNT_L (low)", .{byte}),
+        0x0400_0089 => log.warn("Tried to write 0x{X:0>2} to SOUNDBIAS (high)", .{byte}),
         else => std.debug.panic("Tried to write 0x{X:0>2} to 0x{X:0>8}", .{ byte, addr }),
     }
 }
 
+fn failed_read(comptime format: []const u8, args: anytype) u8 {
+    log.warn(format, args);
+    return 0;
+}
+
 /// Read / Write 
 pub const PostFlag = extern union {
     /// 0 if First Boot, 1 if a Reset has been done

src/cpu.zig

@@ -278,8 +278,8 @@ pub const Arm7tdmi = struct {
             if (!self.bus.io.ime or self.cpsr.i.read()) return;
             // log.info("An interrupt was Handled!", .{});
 
-            // TODO: Should this behave like Software Interrupts?
-            const r15 = self.r[15] + if (self.cpsr.t.read()) @as(u32, 2) else 4;
+            // retAddr.gba says r15 on it's own is off by -04h in both ARM and THUMB mode
+            const r15 = self.r[15] + 4;
             const cpsr = self.cpsr.raw;
 
             self.changeMode(.Irq);