88 lines
2.6 KiB
Zig
88 lines
2.6 KiB
Zig
const std = @import("std");
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const Allocator = std.mem.Allocator;
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const log = std.log.scoped(.Bios);
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const rotr = @import("zba-util").rotr;
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const forceAlign = @import("../Bus.zig").forceAlign;
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/// Size of the BIOS in bytes
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pub const size = 0x4000;
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const Self = @This();
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buf: ?[]u8,
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allocator: Allocator,
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addr_latch: u32 = 0,
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// https://github.com/ITotalJustice/notorious_beeg/issues/106
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pub fn read(self: *Self, comptime T: type, r15: u32, address: u32) T {
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if (r15 < Self.size) {
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const addr = forceAlign(T, address);
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self.addr_latch = addr;
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return self._read(T, addr);
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}
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log.warn("Open Bus! Read from 0x{X:0>8}, but PC was 0x{X:0>8}", .{ address, r15 });
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const value = self._read(u32, self.addr_latch);
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return @truncate(T, rotr(u32, value, 8 * rotateBy(T, address)));
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}
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fn rotateBy(comptime T: type, address: u32) u32 {
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return switch (T) {
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u8 => address & 3,
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u16 => address & 2,
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u32 => 0,
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else => @compileError("bios: unsupported read width"),
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};
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}
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pub fn dbgRead(self: *const Self, comptime T: type, r15: u32, address: u32) T {
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if (r15 < Self.size) return self._read(T, forceAlign(T, address));
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const value = self._read(u32, self.addr_latch);
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return @truncate(T, rotr(u32, value, 8 * rotateBy(T, address)));
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}
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/// Read without the GBA safety checks
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fn _read(self: *const Self, comptime T: type, addr: u32) T {
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const buf = self.buf orelse std.debug.panic("[BIOS] ZBA tried to read {} from 0x{X:0>8} but not BIOS was present", .{ T, addr });
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return switch (T) {
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u32, u16, u8 => std.mem.readIntSliceLittle(T, buf[addr..][0..@sizeOf(T)]),
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else => @compileError("BIOS: Unsupported read width"),
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};
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}
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pub fn write(_: *Self, comptime T: type, addr: u32, value: T) void {
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@setCold(true);
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log.debug("Tried to write {} 0x{X:} to 0x{X:0>8} ", .{ T, value, addr });
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}
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pub fn init(allocator: Allocator, maybe_path: ?[]const u8) !Self {
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if (maybe_path == null) return .{ .buf = null, .allocator = allocator };
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const path = maybe_path.?;
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const buf = try allocator.alloc(u8, Self.size);
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errdefer allocator.free(buf);
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const file = try std.fs.cwd().openFile(path, .{});
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defer file.close();
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const file_len = try file.readAll(buf);
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if (file_len != Self.size) log.err("Expected BIOS to be {}B, was {}B", .{ Self.size, file_len });
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return Self{ .buf = buf, .allocator = allocator };
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}
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pub fn reset(self: *Self) void {
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self.addr_latch = 0;
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}
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pub fn deinit(self: *Self) void {
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if (self.buf) |buf| self.allocator.free(buf);
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self.* = undefined;
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}
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