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feat: implement dedicated Barrel Shifter SHL and SHR

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-01-05 13:58:11 -05:00
parent 7473ffedc7
commit 28a70d0112
6 changed files with 126 additions and 38 deletions
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2
.gitignore vendored
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@ -2,3 +2,5 @@
/bin
/zig-cache
/zig-out
/docs
**/*.log

4
src/cpu.zig
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@ -2,8 +2,10 @@ const std = @import("std");
const util = @import("util.zig");
const bitfield = @import("bitfield");
const BarrelShifter = @import("cpu/barrel_shifter.zig");
const Bus = @import("bus.zig").Bus;
const Scheduler = @import("scheduler.zig").Scheduler;
const Bitfield = bitfield.Bitfield;
const Bit = bitfield.Bit;
@ -160,7 +162,7 @@ fn populate() [0x1000]InstrFn {
};
}
const CPSR = extern union {
pub const CPSR = extern union {
mode: Bitfield(u32, 0, 5),
t: Bit(u32, 5),
f: Bit(u32, 6),

83
src/cpu/barrel_shifter.zig Normal file
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@ -0,0 +1,83 @@
const std = @import("std");
const arm = @import("../cpu.zig");
const Arm7tdmi = arm.Arm7tdmi;
const CPSR = arm.CPSR;
pub inline fn exec(cpu: *Arm7tdmi, opcode: u32) u32 {
var shift_amt: u8 = undefined;
if (opcode >> 4 & 1 == 1) {
shift_amt = @truncate(u8, cpu.r[opcode >> 8 & 0xF]);
} else {
shift_amt = @truncate(u8, opcode >> 7 & 0x1F);
}
const rm = cpu.r[opcode & 0xF];
return switch (@truncate(u2, opcode >> 5)) {
0b00 => logical_left(&cpu.cpsr, rm, shift_amt),
0b01 => logical_right(&cpu.cpsr, rm, shift_amt),
0b10 => arithmetic_right(&cpu.cpsr, rm, shift_amt),
0b11 => rotate_right(&cpu.cpsr, rm, shift_amt),
};
}
pub inline fn logical_left(cpsr: *CPSR, rm: u32, shift_byte: u8) u32 {
const shift_amt = @truncate(u5, shift_byte);
const bit_count: u8 = @typeInfo(u32).Int.bits;
var result: u32 = 0x0000_0000;
if (shift_byte < bit_count) {
// We can perform a well-defined shift here
// FIXME: We assume cpu.r[rs] == 0 and imm_shift == 0 are equivalent
if (shift_amt != 0) {
const carry_bit = @truncate(u5, bit_count - shift_amt);
cpsr.c.write(rm >> carry_bit & 1 == 1);
}
result = rm << shift_amt;
} else if (shift_byte == bit_count) {
// Shifted all bits out, carry bit is bit 0 of rm
cpsr.c.write(rm & 1 == 1);
} else {
// Shifted all bits out, carry bit has also been shifted out
cpsr.c.write(false);
}
return result;
}
pub inline fn logical_right(cpsr: *CPSR, rm: u32, shift_byte: u8) u32 {
const shift_amt = @truncate(u5, shift_byte);
const bit_count: u8 = @typeInfo(u32).Int.bits;
var result: u32 = 0x0000_0000;
if (shift_byte == 0 or shift_byte == bit_count) {
// Actualy LSR #32
cpsr.c.write(rm >> 31 & 1 == 1);
} else if (shift_byte < bit_count) {
// We can perform a well-defined shift
const carry_bit = shift_amt - 1;
cpsr.c.write(rm >> carry_bit & 1 == 1);
result = rm >> shift_amt;
} else {
// All bits have been shifted out, including carry bit
cpsr.c.write(false);
}
return result;
}
pub fn arithmetic_right(_: *CPSR, _: u32, _: u8) u32 {
// @bitCast(u32, @bitCast(i32, r_val) >> @truncate(u5, amount))
std.debug.panic("[BarrelShifter] implement arithmetic shift right", .{});
}
pub fn rotate_right(_: *CPSR, _: u32, _: u8) u32 {
// std.math.rotr(u32, r_val, amount)
std.debug.panic("[BarrelShifter] implement rotate right", .{});
}

45
src/cpu/data_processing.zig
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@ -1,9 +1,10 @@
const std = @import("std");
const processor = @import("../cpu.zig");
const arm = @import("../cpu.zig");
const BarrelShifter = @import("barrel_shifter.zig");
const Bus = @import("../bus.zig").Bus;
const Arm7tdmi = processor.Arm7tdmi;
const InstrFn = processor.InstrFn;
const Arm7tdmi = arm.Arm7tdmi;
const InstrFn = arm.InstrFn;
pub fn comptimeDataProcessing(comptime I: bool, comptime S: bool, comptime instrKind: u4) InstrFn {
return struct {
@ -15,7 +16,7 @@ pub fn comptimeDataProcessing(comptime I: bool, comptime S: bool, comptime instr
if (I) {
op2 = std.math.rotr(u32, opcode & 0xFF, (opcode >> 8 & 0xF) << 1);
} else {
op2 = registerOp2(cpu, opcode);
op2 = BarrelShifter.exec(cpu, opcode);
}
switch (instrKind) {
@ -45,7 +46,7 @@ pub fn comptimeDataProcessing(comptime I: bool, comptime S: bool, comptime instr
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
cpu.cpsr.c.write(op2 <= op1_val);
cpu.cpsr.v.write(v_ctx and (result >> 31 & 1== 1));
cpu.cpsr.v.write(v_ctx and (result >> 31 & 1 == 1));
},
else => std.debug.panic("[CPU] TODO: implement data processing type {}", .{instrKind}),
}
@ -53,22 +54,22 @@ pub fn comptimeDataProcessing(comptime I: bool, comptime S: bool, comptime instr
}.dataProcessing;
}
fn registerOp2(cpu: *const Arm7tdmi, opcode: u32) u32 {
var amount: u32 = undefined;
if (opcode >> 4 & 0x01 == 0x01) {
amount = cpu.r[opcode >> 8 & 0xF] & 0xFF;
} else {
amount = opcode >> 7 & 0x1F;
}
// fn registerOp2(cpu: *const Arm7tdmi, opcode: u32) u32 {
// var amount: u32 = undefined;
// if (opcode >> 4 & 0x01 == 0x01) {
// amount = cpu.r[opcode >> 8 & 0xF] & 0xFF;
// } else {
// amount = opcode >> 7 & 0x1F;
// }
const rm = opcode & 0xF;
const r_val = cpu.r[rm];
// const rm = opcode & 0xF;
// const r_val = cpu.r[rm];
return switch (opcode >> 5 & 0x03) {
0b00 => r_val << @truncate(u5, amount),
0b01 => r_val >> @truncate(u5, amount),
0b10 => @bitCast(u32, @bitCast(i32, r_val) >> @truncate(u5, amount)),
0b11 => std.math.rotr(u32, r_val, amount),
else => unreachable,
};
}
// return switch (opcode >> 5 & 0x03) {
// 0b00 => r_val << @truncate(u5, amount),
// 0b01 => r_val >> @truncate(u5, amount),
// 0b10 => @bitCast(u32, @bitCast(i32, r_val) >> @truncate(u5, amount)),
// 0b11 => std.math.rotr(u32, r_val, amount),
// else => unreachable,
// };
// }

6
src/cpu/half_signed_data_transfer.zig
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@ -1,10 +1,10 @@
const std = @import("std");
const processor = @import("../cpu.zig");
const arm = @import("../cpu.zig");
const util = @import("../util.zig");
const Bus = @import("../bus.zig").Bus;
const Arm7tdmi = processor.Arm7tdmi;
const InstrFn = processor.InstrFn;
const Arm7tdmi = arm.Arm7tdmi;
const InstrFn = arm.InstrFn;
pub fn comptimeHalfSignedDataTransfer(comptime P: bool, comptime U: bool, comptime I: bool, comptime W: bool, comptime L: bool) InstrFn {
return struct {

24
src/cpu/single_data_transfer.zig
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@ -1,10 +1,11 @@
const std = @import("std");
const util = @import("../util.zig");
const processor = @import("../cpu.zig");
const arm = @import("../cpu.zig");
const BarrelShifter = @import("barrel_shifter.zig");
const Bus = @import("../bus.zig").Bus;
const Arm7tdmi = processor.Arm7tdmi;
const InstrFn = processor.InstrFn;
const Arm7tdmi = arm.Arm7tdmi;
const InstrFn = arm.InstrFn;
pub fn comptimeSingleDataTransfer(comptime I: bool, comptime P: bool, comptime U: bool, comptime B: bool, comptime W: bool, comptime L: bool) InstrFn {
return struct {
@ -48,15 +49,14 @@ pub fn comptimeSingleDataTransfer(comptime I: bool, comptime P: bool, comptime U
}
fn registerOffset(cpu: *Arm7tdmi, opcode: u32) u32 {
const amount = opcode >> 7 & 0x1F;
const rm = opcode & 0xF;
const r_val = cpu.r[rm];
const shift_byte = @truncate(u8, opcode >> 7 & 0x1F);
return switch (opcode >> 5 & 0x03) {
0b00 => r_val << @truncate(u5, amount),
0b01 => r_val >> @truncate(u5, amount),
0b10 => @bitCast(u32, @bitCast(i32, r_val) >> @truncate(u5, amount)),
0b11 => std.math.rotr(u32, r_val, amount),
else => unreachable,
const rm = cpu.r[opcode & 0xF];
return switch (@truncate(u2, opcode >> 5)) {
0b00 => BarrelShifter.logical_left(&cpu.cpsr, rm, shift_byte),
0b01 => BarrelShifter.logical_right(&cpu.cpsr, rm, shift_byte),
0b10 => BarrelShifter.arithmetic_right(&cpu.cpsr, rm, shift_byte),
0b11 => BarrelShifter.rotate_right(&cpu.cpsr, rm, shift_byte),
};
}