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fix: rotate unaligned reads on BIOS open-bus

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This commit is contained in:
Rekai Nyangadzayi Musuka
2022-12-27 05:41:19 -06:00
parent 39d50466c9
commit db7a562aa2
2 changed files with 24 additions and 7 deletions
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8
src/core/Bus.zig
View File

@@ -227,7 +227,7 @@ fn dbgSlowRead(self: *const Self, comptime T: type, unaligned_address: u32) T {
// General Internal Memory
0x00 => blk: {
if (address < Bios.size)
break :blk self.bios.dbgRead(T, self.cpu.r[15], address);
break :blk self.bios.dbgRead(T, self.cpu.r[15], unaligned_address);
break :blk self.openBus(T, address);
},
@@ -347,7 +347,7 @@ fn slowRead(self: *Self, comptime T: type, unaligned_address: u32) T {
// General Internal Memory
0x00 => blk: {
if (address < Bios.size)
break :blk self.bios.read(T, self.cpu.r[15], address);
break :blk self.bios.read(T, self.cpu.r[15], unaligned_address);
break :blk self.openBus(T, address);
},
@@ -437,11 +437,11 @@ inline fn rotateBy(comptime T: type, address: u32) u32 {
u32 => address & 3,
u16 => address & 1,
u8 => 0,
else => @compileError("Backup: Unsupported write width"),
else => @compileError("Unsupported write width"),
};
}
inline fn forceAlign(comptime T: type, address: u32) u32 {
pub inline fn forceAlign(comptime T: type, address: u32) u32 {
return switch (T) {
u32 => address & ~@as(u32, 3),
u16 => address & ~@as(u32, 1),

23
src/core/bus/Bios.zig
View File

@@ -3,6 +3,9 @@ const std = @import("std");
const Allocator = std.mem.Allocator;
const log = std.log.scoped(.Bios);
const rotr = @import("../../util.zig").rotr;
const forceAlign = @import("../Bus.zig").forceAlign;
/// Size of the BIOS in bytes
pub const size = 0x4000;
const Self = @This();
@@ -12,14 +15,28 @@ allocator: Allocator,
addr_latch: u32,
pub fn read(self: *Self, comptime T: type, r15: u32, addr: u32) T {
// https://github.com/ITotalJustice/notorious_beeg/issues/106
pub fn read(self: *Self, comptime T: type, r15: u32, address: u32) T {
if (r15 < Self.size) {
const addr = forceAlign(T, address);
self.addr_latch = addr;
return self._read(T, addr);
}
log.debug("Rejected read since r15=0x{X:0>8}", .{r15});
return @truncate(T, self._read(T, self.addr_latch));
log.warn("Open Bus! Read from 0x{X:0>8}, but PC was 0x{X:0>8}", .{ address, r15 });
const value = self._read(u32, self.addr_latch);
return @truncate(T, rotr(u32, value, 8 * rotateBy(T, address)));
}
fn rotateBy(comptime T: type, address: u32) u32 {
return switch (T) {
u8 => address & 3,
u16 => address & 2,
u32 => 0,
else => @compileError("bios: unsupported read width"),
};
}
pub fn dbgRead(self: *const Self, comptime T: type, r15: u32, addr: u32) T {