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chore(cpu): reimplement bank switching logic

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-02-12 04:33:32 -04:00
parent d897c2fdcc
commit 8ab7a178c1
1 changed files with 56 additions and 53 deletions
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109
src/cpu.zig
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@ -97,8 +97,8 @@ pub const Arm7tdmi = struct {
self.binary_log = is_binary;
}
inline fn bankedIdx(mode: Mode) usize {
return switch (mode) {
inline fn bankedIdx(mode: Mode, kind: BankedKind) usize {
const idx: usize = switch (mode) {
.User, .System => 0,
.Supervisor => 1,
.Abort => 2,
@ -106,9 +106,11 @@ pub const Arm7tdmi = struct {
.Irq => 4,
.Fiq => 5,
};
return (idx * 2) + if (kind == .R14) @as(usize, 1) else 0;
}
inline fn spsrIdx(mode: Mode) usize {
inline fn bankedSpsrIndex(mode: Mode) usize {
return switch (mode) {
.Supervisor => 0,
.Abort => 1,
@ -119,6 +121,10 @@ pub const Arm7tdmi = struct {
};
}
inline fn bankedFiqIdx(i: usize, mode: Mode) usize {
return (i * 2) + if (mode == .Fiq) @as(usize, 1) else 0;
}
pub inline fn hasSPSR(self: *const Self) bool {
const mode = getModeChecked(self, self.cpsr.mode.read());
return switch (mode) {
@ -147,84 +153,77 @@ pub const Arm7tdmi = struct {
pub fn setUserModeRegister(self: *Self, idx: usize, value: u32) void {
const current = getModeChecked(self, self.cpsr.mode.read());
if (idx < 8) {
self.r[idx] = value;
} else if (idx < 13) {
if (current == .Fiq) {
const user_offset: usize = 0;
self.banked_fiq[(idx - 8) * 2 + user_offset] = value;
} else self.r[idx] = value;
} else if (idx < 15) {
switch (current) {
switch (idx) {
8...12 => {
if (current == .Fiq) {
self.banked_fiq[bankedFiqIdx(idx - 8, .User)] = value;
} else self.r[idx] = value;
},
13, 14 => switch (current) {
.User, .System => self.r[idx] = value,
else => {
self.banked_r[bankedIdx(.User) * 2 + (idx - 13)] = value;
const kind = std.meta.intToEnum(BankedKind, idx - 13) catch unreachable;
self.banked_r[bankedIdx(.User, kind)] = value;
},
}
} else self.r[idx] = value;
},
else => self.r[idx] = value, // R0 -> R7 and R15
}
}
pub fn getUserModeRegister(self: *Self, idx: usize) u32 {
const current = getModeChecked(self, self.cpsr.mode.read());
var result: u32 = undefined;
if (idx < 8) {
result = self.r[idx];
} else if (idx < 13) {
if (current == .Fiq) {
const user_offset: usize = 0;
result = self.banked_fiq[(idx - 8) * 2 + user_offset];
} else result = self.r[idx];
} else if (idx < 15) {
switch (current) {
.User, .System => result = self.r[idx],
else => {
result = self.banked_r[bankedIdx(.User) * 2 + (idx - 13)];
return switch (idx) {
8...12 => if (current == .Fiq) self.banked_fiq[bankedFiqIdx(idx - 8, .User)] else self.r[idx],
13, 14 => switch (current) {
.User, .System => self.r[idx],
else => blk: {
const kind = std.meta.intToEnum(BankedKind, idx - 13) catch unreachable;
break :blk self.banked_r[bankedIdx(.User, kind)];
},
}
} else result = self.r[idx];
return result;
},
else => self.r[idx], // R0 -> R7 and R15
};
}
pub fn changeMode(self: *Self, next: Mode) void {
const now = getModeChecked(self, self.cpsr.mode.read());
// Bank R8 -> r12
var r: usize = 8;
while (r <= 12) : (r += 1) {
self.banked_fiq[(r - 8) * 2 + if (now == .Fiq) @as(usize, 1) else 0] = self.r[r];
var i: usize = 0;
while (i < 5) : (i += 1) {
self.banked_fiq[bankedFiqIdx(i, now)] = self.r[8 + i];
}
// Bank r13, r14, SPSR
switch (now) {
.User, .System => {
self.banked_r[bankedIdx(now) * 2 + 0] = self.r[13];
self.banked_r[bankedIdx(now) * 2 + 1] = self.r[14];
self.banked_r[bankedIdx(now, .R13)] = self.r[13];
self.banked_r[bankedIdx(now, .R14)] = self.r[14];
},
else => {
self.banked_r[bankedIdx(now) * 2 + 0] = self.r[13];
self.banked_r[bankedIdx(now) * 2 + 1] = self.r[14];
self.banked_spsr[spsrIdx(now)] = self.spsr;
self.banked_r[bankedIdx(now, .R13)] = self.r[13];
self.banked_r[bankedIdx(now, .R14)] = self.r[14];
self.banked_spsr[bankedSpsrIndex(now)] = self.spsr;
},
}
// Grab R8 -> R12
r = 8;
while (r <= 12) : (r += 1) {
self.r[r] = self.banked_fiq[(r - 8) * 2 + if (next == .Fiq) @as(usize, 1) else 0];
i = 0;
while (i < 5) : (i += 1) {
self.r[8 + i] = self.banked_fiq[bankedFiqIdx(i, next)];
}
// Grab r13, r14, SPSR
switch (next) {
.User, .System => {
self.r[13] = self.banked_r[bankedIdx(next) * 2 + 0];
self.r[14] = self.banked_r[bankedIdx(next) * 2 + 1];
self.r[13] = self.banked_r[bankedIdx(next, .R13)];
self.r[14] = self.banked_r[bankedIdx(next, .R14)];
},
else => {
self.r[13] = self.banked_r[bankedIdx(next) * 2 + 0];
self.r[14] = self.banked_r[bankedIdx(next) * 2 + 1];
self.spsr = self.banked_spsr[spsrIdx(next)];
self.r[13] = self.banked_r[bankedIdx(next, .R13)];
self.r[14] = self.banked_r[bankedIdx(next, .R14)];
self.spsr = self.banked_spsr[bankedSpsrIndex(next)];
},
}
@ -232,16 +231,15 @@ pub const Arm7tdmi = struct {
}
pub fn fastBoot(self: *Self) void {
self.r = std.mem.zeroes([16]u32);
self.r[0] = 0x08000000;
self.r[1] = 0x000000EA;
// GPRs 2 -> 12 *should* already be 0 initialized
self.r[13] = 0x0300_7F00;
self.r[14] = 0x0000_0000;
self.r[15] = 0x0800_0000;
// Set r13_irq and r14_svc to their respective values
self.banked_r[bankedIdx(.Irq) * 2 + 0] = 0x0300_7FA0;
self.banked_r[bankedIdx(.Supervisor) * 2 + 0] = 0x0300_7FE0;
self.banked_r[bankedIdx(.Irq, .R13)] = 0x0300_7FA0;
self.banked_r[bankedIdx(.Supervisor, .R13)] = 0x0300_7FE0;
self.cpsr.raw = 0x6000001F;
}
@ -632,6 +630,11 @@ const Mode = enum(u5) {
System = 0b11111,
};
const BankedKind = enum(u1) {
R13 = 0,
R14,
};
fn getMode(bits: u5) ?Mode {
return std.meta.intToEnum(Mode, bits) catch null;
}