feat: pass jsmolka's bios.gba

README.md

@@ -7,7 +7,7 @@ An in-progress Gameboy Advance Emulator written in Zig ⚡!
     - [x] `flash64.gba`, `flash128.gba`, `none.gba`, and `sram.gba`
     - [x] `hello.gba`, `shades.gba`, and `stripes.gba`
     - [x] `memory.gba`
-    - [ ] `bios.gba`
+    - [x] `bios.gba`
     - [ ] `nes.gba`
 - [ ] [DenSinH's GBA ROMs](https://github.com/DenSinH/GBARoms)
     - [x] `eeprom-test`

src/Bus.zig

@@ -108,7 +108,7 @@ fn readOpenBus(self: *const Self, comptime T: type, address: u32) T {
 }
 
 fn readBios(self: *const Self, comptime T: type, address: u32) T {
-    if (address < Bios.size) return self.bios.read(T, alignAddress(T, address));
+    if (address < Bios.size) return self.bios.checkedRead(T, self.cpu.?.r[15], alignAddress(T, address));
 
     return self.readOpenBus(T, address);
 }

src/bus/Bios.zig

@@ -10,6 +10,8 @@ const Self = @This();
 buf: ?[]u8,
 alloc: Allocator,
 
+addr_latch: u32,
+
 pub fn init(alloc: Allocator, maybe_path: ?[]const u8) !Self {
     var buf: ?[]u8 = null;
     if (maybe_path) |path| {
@@ -21,6 +23,7 @@ pub fn init(alloc: Allocator, maybe_path: ?[]const u8) !Self {
     return Self{
         .buf = buf,
         .alloc = alloc,
+        .addr_latch = 0,
     };
 }
 
@@ -28,13 +31,21 @@ pub fn deinit(self: Self) void {
     if (self.buf) |buf| self.alloc.free(buf);
 }
 
-pub fn read(self: *const Self, comptime T: type, addr: usize) T {
-    if (self.buf) |buf| {
-        if (addr > buf.len) {
-            log.debug("Tried to read {} from {X:0>8} (open bus)", .{ T, addr });
-            return 0;
-        }
+pub fn checkedRead(self: *const Self, comptime T: type, r15: u32, addr: u32) T {
+    if (r15 < Self.size) {
+        // FIXME: Just give up on *const Self on bus reads, Rekai
+        const this = @intToPtr(*Self, @ptrToInt(self));
+        this.addr_latch = addr;
 
+        return self.read(T, addr);
+    }
+
+    log.info("Rejected read since r15=0x{X:0>8}", .{r15});
+    return @truncate(T, self.read(T, self.addr_latch + 8));
+}
+
+fn read(self: *const Self, comptime T: type, addr: u32) T {
+    if (self.buf) |buf| {
         return switch (T) {
             u32 => (@as(u32, buf[addr + 3]) << 24) | (@as(u32, buf[addr + 2]) << 16) | (@as(u32, buf[addr + 1]) << 8) | (@as(u32, buf[addr])),
             u16 => (@as(u16, buf[addr + 1]) << 8) | @as(u16, buf[addr]),
@@ -46,7 +57,7 @@ pub fn read(self: *const Self, comptime T: type, addr: usize) T {
     std.debug.panic("[BIOS] ZBA tried to read {} from 0x{X:0>8} but not BIOS was present", .{ T, addr });
 }
 
-pub fn write(_: *Self, comptime T: type, addr: usize, value: T) void {
+pub fn write(_: *Self, comptime T: type, addr: u32, value: T) void {
     @setCold(true);
     log.debug("Tried to write {} 0x{X:} to 0x{X:0>8} ", .{ T, value, addr });
 }