chore(bios): impl bios handlers

src/core/nds9/Bios.zig

@@ -0,0 +1,49 @@
+const std = @import("std");
+
+const Allocator = std.mem.Allocator;
+
+const log = std.log.scoped(.nds7_bios);
+
+const KiB = 0x400;
+
+const _len = 4 * KiB; // real size of the NDS9 BIOS
+const len = 32 * KiB; // size allocated to NDS9 BIOS
+
+buf: ?*align(4) [len]u8 = null,
+
+// FIXME: Currently we dupe here, should we just take ownership?
+pub fn load(self: *@This(), allocator: Allocator, data: []u8) !void {
+    if (data.len != _len) {
+        const acutal_size = @as(f32, @floatFromInt(data.len)) / KiB;
+        log.warn("BIOS was {d:.2} KiB (should be {} KiB)", .{ acutal_size, len });
+    }
+
+    const buf = try allocator.alignedAlloc(u8, 4, len);
+    @memcpy(buf[0..data.len], data);
+    @memset(buf[data.len..], 0);
+
+    self.* = .{ .buf = buf[0..len] };
+}
+
+pub fn deinit(self: @This(), allocator: Allocator) void {
+    if (self.buf) |ptr| allocator.destroy(ptr);
+}
+
+// Note: Parts of 16MiB addrspace that aren't mapped to BIOS are typically undefined
+pub fn read(self: *const @This(), comptime T: type, address: u32) T {
+    const readInt = std.mem.readIntLittle;
+    const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
+
+    // if (address >= len) return 0x0000_0000; // TODO: What is undefined actually?
+
+    const ptr = self.buf orelse {
+        log.err("read(T: {}, address: 0x{X:0>8}) from BIOS but none was found!", .{ T, address });
+        @panic("TODO: ability to load in NDS9 BIOS just-in-time");
+    };
+
+    return readInt(T, ptr[address & (len - 1) ..][0..byte_count]);
+}
+
+pub fn write(_: *const @This(), comptime T: type, address: u32, value: T) void {
+    log.err("write(T: {}, address: 0x{X:0>8}, value: 0x{X:}) but we're in the BIOS!", .{ T, address, value });
+}