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chore(cpu): iron out some false assumptions

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-01-01 03:41:50 -06:00
parent c660ca8922
commit 92a06e49c3
4 changed files with 128 additions and 36 deletions
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113
src/cpu.zig
View File

@ -1,4 +1,5 @@
const std = @import("std");
const util = @import("util.zig");
const Bus = @import("bus.zig").Bus;
const Scheduler = @import("scheduler.zig").Scheduler;
@ -16,12 +17,11 @@ pub const ARM7TDMI = struct {
cpsr: CPSR,
pub fn new(scheduler: *Scheduler, bus: *Bus) @This() {
const cpsr: u32 = 0x0000_00DF;
return .{
.r = [_]u32{0x00} ** 16,
.sch = scheduler,
.bus = bus,
.cpsr = @bitCast(CPSR, cpsr),
.cpsr = .{ .inner = 0x0000_00DF },
};
}
@ -47,7 +47,7 @@ pub const ARM7TDMI = struct {
};
fn armIdx(opcode: u32) u12 {
return @truncate(u12, opcode >> 20 & 0xFF) << 4 | @truncate(u12, opcode >> 8 & 0xF);
return @truncate(u12, opcode >> 20 & 0xFF) << 4 | @truncate(u12, opcode >> 4 & 0xF);
}
fn populate() [0x1000]InstrFn {
@ -65,29 +65,18 @@ fn populate() [0x1000]InstrFn {
lut[i] = comptimeDataProcessing(I, S, instrKind);
}
if (i >> 9 & 0x7 == 0b000 and i >> 6 & 0x01 == 0x00 and i & 0xF == 0x0) {
if (i >> 9 & 0x7 == 0b000 and i >> 3 & 0x01 == 0x01 and i & 0x01 == 0x01) {
// Halfword and Signed Data Transfer with register offset
const P = i >> 8 & 0x01 == 0x01;
const U = i >> 7 & 0x01 == 0x01;
const I = true;
const I = i >> 6 & 0x01 == 0x01;
const W = i >> 5 & 0x01 == 0x01;
const L = i >> 4 & 0x01 == 0x01;
lut[i] = comptimeHalfSignedDataTransfer(P, U, I, W, L);
}
if (i >> 9 & 0x7 == 0b000 and i >> 6 & 0x01 == 0x01) {
// Halfword and Signed Data Tranfer with immediate offset
const P = i >> 8 & 0x01 == 0x01;
const U = i >> 7 & 0x01 == 0x01;
const I = false;
const W = i >> 5 & 0x01 == 0x01;
const L = i >> 4 & 0x01 == 0x01;
lut[i] = comptimeHalfSignedDataTransfer(P, U, I, W, L);
}
if (i >> 10 & 0x3 == 0b01 and i & 0x01 == 0x00) {
if (i >> 10 & 0x3 == 0b01) {
const I = i >> 9 & 0x01 == 0x01;
const P = i >> 8 & 0x01 == 0x01;
const U = i >> 7 & 0x01 == 0x01;
@ -108,22 +97,85 @@ fn populate() [0x1000]InstrFn {
};
}
const CPSR = packed struct {
n: bool, // Negative / Less Than
z: bool, // Zero
c: bool, // Carry / Borrow / Extend
v: bool, // Overflow
_: u20,
i: bool, // IRQ Disable
f: bool, // FIQ Diable
t: bool, // State
m: Mode, // Mode
const CPSR = struct {
inner: u32,
pub fn n(self: *const @This()) bool {
return self.inner >> 31 & 0x01 == 0x01;
}
pub fn set_n(self: *@This(), set: bool) void {
self.set_bit(31, set);
}
pub fn z(self: *const @This()) bool {
return self.inner >> 30 & 0x01 == 0x01;
}
pub fn set_z(self: *@This(), set: bool) void {
self.set_bit(30, set);
}
pub fn c(self: *const @This()) bool {
return self.inner >> 29 & 0x01 == 0x01;
}
pub fn set_c(self: *@This(), set: bool) void {
self.set_bit(29, set);
}
pub fn v(self: *const @This()) bool {
return self.inner >> 28 & 0x01 == 0x01;
}
pub fn set_v(self: *@This(), set: bool) void {
self.set_bit(28, set);
}
pub fn i(self: *const @This()) bool {
return self.inner >> 7 & 0x01 == 0x01;
}
pub fn set_i(self: *@This(), set: bool) void {
self.set_bit(7, set);
}
pub fn f(self: *const @This()) bool {
return self.inner >> 6 & 0x01 == 0x01;
}
pub fn set_f(self: *@This(), set: bool) void {
self.set_bit(6, set);
}
pub fn t(self: *const @This()) bool {
return self.inner >> 5 & 0x01 == 0x01;
}
pub fn set_t(self: *@This(), set: bool) void {
self.set_bit(5, set);
}
pub fn mode(self: *const @This()) Mode {
return self.inner & 0x1F;
}
pub fn set_mode(_: *@This(), _: Mode) void {
std.debug.panic("TODO: Implement set_mode for CPSR", .{});
}
fn set_bit(self: *@This(), comptime bit: usize, set: bool) void {
const set_val = @as(u32, @boolToInt(set)) << bit;
const mask = ~(@as(u32, 1) << bit);
self.inner = (self.inner & mask) | set_val;
}
};
const Mode = enum(u5) {
User = 0b10000,
Fiq = 0b10001,
Irq = 0b10010,
FIQ = 0b10001,
IRQ = 0b10010,
Supervisor = 0b10011,
Abort = 0b10111,
Undefined = 0b11011,
@ -142,8 +194,7 @@ fn comptimeBranch(comptime L: bool) InstrFn {
cpu.r[14] = cpu.r[15] - 4;
}
const offset = @bitCast(i32, (opcode << 2) << 8) >> 8;
cpu.r[15] = cpu.fakePC() + @bitCast(u32, offset);
cpu.r[15] = cpu.fakePC() + util.u32SignExtend(24, opcode << 2);
}
}.branch;
}

17
src/cpu/data_processing.zig
View File

@ -20,15 +20,32 @@ pub fn comptimeDataProcessing(comptime I: bool, comptime S: bool, comptime instr
switch (instrKind) {
0x4 => {
// ADD
cpu.r[rd] = cpu.r[op1] + op2;
if (S) std.debug.panic("TODO: implement ADD condition codes", .{});
},
0xD => {
// MOV
cpu.r[rd] = op2;
if (S) std.debug.panic("TODO: implement MOV condition codes", .{});
},
0xA => {
// CMP
var result: u32 = undefined;
const op1_val = cpu.r[op1];
const v_ctx = (op1_val >> 31 == 0x01) or (op2 >> 31 == 0x01);
const didOverflow = @subWithOverflow(u32, op1_val, op2, &result);
cpu.cpsr.set_v(v_ctx and (result >> 31 & 0x01 == 0x01));
cpu.cpsr.set_c(didOverflow);
cpu.cpsr.set_z(result == 0x00);
cpu.cpsr.set_n(result >> 31 & 0x01 == 0x01);
},
else => std.debug.panic("TODO: implement data processing type {}", .{instrKind}),
}
}

4
src/cpu/half_signed_data_transfer.zig
View File

@ -40,12 +40,12 @@ pub fn comptimeHalfSignedDataTransfer(comptime P: bool, comptime U: bool, compti
0b10 => {
// LDRSB
const byte = bus.readByte(address);
cpu.r[rd] = util.u32_sign_extend(@as(u32, byte), 8);
cpu.r[rd] = util.u32SignExtend(8, @as(u32, byte));
},
0b11 => {
// LDRSH
const halfword = bus.readHalfWord(address);
cpu.r[rd] = util.u32_sign_extend(@as(u32, halfword), 16);
cpu.r[rd] = util.u32SignExtend(16, @as(u32, halfword));
},
}
} else {

30
src/util.zig
View File

@ -1,6 +1,30 @@
const std = @import("std");
const assert = std.debug.assert;
pub fn u32_sign_extend(value: u32, bitSize: anytype) u32 {
const amount: u5 = 32 - bitSize;
return @bitCast(u32, @bitCast(i32, value << amount) >> amount);
pub fn signExtend(comptime T: type, comptime bits: usize, value: anytype) T {
const ValT = comptime @TypeOf(value);
comptime assert(isInteger(ValT));
comptime assert(isSigned(ValT));
const value_bits = @typeInfo(ValT).Int.bits;
comptime assert(value_bits >= bits);
const bit_diff = value_bits - bits;
// (1 << bits) -1 is a mask that will take values like 0x100 and make them 0xFF
// value & mask so that only the relevant bits are sign extended
// therefore, value & ((1 << bits) - 1) is the isolation of the relevant bits
return ((value & ((1 << bits) - 1)) << bit_diff) >> bit_diff;
}
pub fn u32SignExtend(comptime bits: usize, value: u32) u32 {
return @bitCast(u32, signExtend(i32, bits, @bitCast(i32, value)));
}
fn isInteger(comptime T: type) bool {
return @typeInfo(T) == .Int;
}
fn isSigned(comptime T: type) bool {
return @typeInfo(T).Int.signedness == .signed;
}