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Chirp/src/cpu/instruction.rs

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// (c) 2023 John A. Breaux
// This code is licensed under MIT license (see LICENSE.txt for details)
//! Contains implementations for each [Insn] as private member functions of [CPU]
use super::*;
impl CPU {
/// Executes a single [Insn]
#[inline(always)]
#[rustfmt::skip]
pub(super) fn execute(&mut self, bus: &mut Bus, instruction: Insn) {
match instruction {
// Core Chip-8 instructions
Insn::cls => self.clear_screen(bus),
Insn::ret => self.ret(bus),
Insn::jmp { A } => self.jump(A),
Insn::call { A } => self.call(A, bus),
Insn::seb { x, B } => self.skip_equals_immediate(x, B),
Insn::sneb { x, B } => self.skip_not_equals_immediate(x, B),
Insn::se { y, x } => self.skip_equals(x, y),
Insn::movb { x, B } => self.load_immediate(x, B),
Insn::addb { x, B } => self.add_immediate(x, B),
Insn::mov { y, x } => self.load(x, y),
Insn::or { y, x } => self.or(x, y),
Insn::and { y, x } => self.and(x, y),
Insn::xor { y, x } => self.xor(x, y),
Insn::add { y, x } => self.add(x, y),
Insn::sub { y, x } => self.sub(x, y),
Insn::shr { y, x } => self.shift_right(x, y),
Insn::bsub { y, x } => self.backwards_sub(x, y),
Insn::shl { y, x } => self.shift_left(x, y),
Insn::sne { y, x } => self.skip_not_equals(x, y),
Insn::movI { A } => self.load_i_immediate(A),
Insn::jmpr { A } => self.jump_indexed(A),
Insn::rand { x, B } => self.rand(x, B),
Insn::draw { y, x, n } => self.draw(x, y, n, bus),
Insn::sek { x } => self.skip_key_equals(x),
Insn::snek { x } => self.skip_key_not_equals(x),
Insn::getdt { x } => self.load_delay_timer(x),
Insn::waitk { x } => self.wait_for_key(x),
Insn::setdt { x } => self.store_delay_timer(x),
Insn::movst { x } => self.store_sound_timer(x),
Insn::addI { x } => self.add_i(x),
Insn::font { x } => self.load_sprite(x),
Insn::bcd { x } => self.bcd_convert(x, bus),
Insn::dmao { x } => self.store_dma(x, bus),
Insn::dmai { x } => self.load_dma(x, bus),
// Super-Chip extensions
Insn::scd { n } => self.scroll_down(n, bus),
Insn::scr => self.scroll_right(bus),
Insn::scl => self.scroll_left(bus),
Insn::halt => self.flags.pause(),
Insn::lores => self.init_lores(bus),
Insn::hires => self.init_hires(bus),
Insn::hfont { x } => self.load_big_sprite(x),
Insn::flgo { x } => self.store_flags(x, bus),
Insn::flgi { x } => self.load_flags(x, bus),
}
}
}
// |`0aaa`| Issues a "System call" (ML routine)
//
// |opcode| effect |
// |------|------------------------------------|
// |`00e0`| Clear screen memory to all 0 |
// |`00ee`| Return from subroutine |
impl CPU {
/// |`00e0`| Clears the screen memory to 0
#[inline(always)]
pub(super) fn clear_screen(&mut self, bus: &mut Bus) {
bus.clear_region(Region::Screen);
}
/// |`00ee`| Returns from subroutine
#[inline(always)]
pub(super) fn ret(&mut self, bus: &impl ReadWrite<u16>) {
self.sp = self.sp.wrapping_add(2);
self.pc = bus.read(self.sp);
}
}
// |`1aaa`| Sets pc to an absolute address
impl CPU {
/// |`1aaa`| Sets the program counter to an absolute address
#[inline(always)]
pub(super) fn jump(&mut self, a: Adr) {
// jump to self == halt
if a.wrapping_add(2) == self.pc {
self.flags.pause = true;
}
self.pc = a;
}
}
// |`2aaa`| Pushes pc onto the stack, then jumps to a
impl CPU {
/// |`2aaa`| Pushes pc onto the stack, then jumps to a
#[inline(always)]
pub(super) fn call(&mut self, a: Adr, bus: &mut impl ReadWrite<u16>) {
bus.write(self.sp, self.pc);
self.sp = self.sp.wrapping_sub(2);
self.pc = a;
}
}
// |`3xbb`| Skips next instruction if register X == b
impl CPU {
/// |`3xbb`| Skips the next instruction if register X == b
#[inline(always)]
pub(super) fn skip_equals_immediate(&mut self, x: Reg, b: u8) {
if self.v[x] == b {
self.pc = self.pc.wrapping_add(2);
}
}
}
// |`4xbb`| Skips next instruction if register X != b
impl CPU {
/// |`4xbb`| Skips the next instruction if register X != b
#[inline(always)]
pub(super) fn skip_not_equals_immediate(&mut self, x: Reg, b: u8) {
if self.v[x] != b {
self.pc = self.pc.wrapping_add(2);
}
}
}
// |`5xyn`| Performs a register-register comparison
//
// |opcode| effect |
// |------|------------------------------------|
// |`5XY0`| Skip next instruction if vX == vY |
impl CPU {
/// |`5xy0`| Skips the next instruction if register X != register Y
#[inline(always)]
pub(super) fn skip_equals(&mut self, x: Reg, y: Reg) {
if self.v[x] == self.v[y] {
self.pc = self.pc.wrapping_add(2);
}
}
}
// |`6xbb`| Loads immediate byte b into register vX
impl CPU {
/// |`6xbb`| Loads immediate byte b into register vX
#[inline(always)]
pub(super) fn load_immediate(&mut self, x: Reg, b: u8) {
self.v[x] = b;
}
}
// |`7xbb`| Adds immediate byte b to register vX
impl CPU {
/// |`7xbb`| Adds immediate byte b to register vX
#[inline(always)]
pub(super) fn add_immediate(&mut self, x: Reg, b: u8) {
self.v[x] = self.v[x].wrapping_add(b);
}
}
// |`8xyn`| Performs ALU operation
//
// |opcode| effect |
// |------|------------------------------------|
// |`8xy0`| Y = X |
// |`8xy1`| X = X | Y |
// |`8xy2`| X = X & Y |
// |`8xy3`| X = X ^ Y |
// |`8xy4`| X = X + Y; Set vF=carry |
// |`8xy5`| X = X - Y; Set vF=carry |
// |`8xy6`| X = X >> 1 |
// |`8xy7`| X = Y - X; Set vF=carry |
// |`8xyE`| X = X << 1 |
impl CPU {
/// |`8xy0`| Loads the value of y into x
#[inline(always)]
pub(super) fn load(&mut self, x: Reg, y: Reg) {
self.v[x] = self.v[y];
}
/// |`8xy1`| Performs bitwise or of vX and vY, and stores the result in vX
///
/// # Quirk
/// The original chip-8 interpreter will clobber vF for any 8-series instruction
#[inline(always)]
pub(super) fn or(&mut self, x: Reg, y: Reg) {
self.v[x] |= self.v[y];
if !self.flags.quirks.bin_ops {
self.v[0xf] = 0;
}
}
/// |`8xy2`| Performs bitwise and of vX and vY, and stores the result in vX
///
/// # Quirk
/// The original chip-8 interpreter will clobber vF for any 8-series instruction
#[inline(always)]
pub(super) fn and(&mut self, x: Reg, y: Reg) {
self.v[x] &= self.v[y];
if !self.flags.quirks.bin_ops {
self.v[0xf] = 0;
}
}
/// |`8xy3`| Performs bitwise xor of vX and vY, and stores the result in vX
///
/// # Quirk
/// The original chip-8 interpreter will clobber vF for any 8-series instruction
#[inline(always)]
pub(super) fn xor(&mut self, x: Reg, y: Reg) {
self.v[x] ^= self.v[y];
if !self.flags.quirks.bin_ops {
self.v[0xf] = 0;
}
}
/// |`8xy4`| Performs addition of vX and vY, and stores the result in vX
#[inline(always)]
pub(super) fn add(&mut self, x: Reg, y: Reg) {
let carry;
(self.v[x], carry) = self.v[x].overflowing_add(self.v[y]);
self.v[0xf] = carry.into();
}
/// |`8xy5`| Performs subtraction of vX and vY, and stores the result in vX
#[inline(always)]
pub(super) fn sub(&mut self, x: Reg, y: Reg) {
let carry;
(self.v[x], carry) = self.v[x].overflowing_sub(self.v[y]);
self.v[0xf] = (!carry).into();
}
/// |`8xy6`| Performs bitwise right shift of vX
///
/// # Quirk
/// On the original chip-8 interpreter, this shifts vY and stores the result in vX
#[inline(always)]
pub(super) fn shift_right(&mut self, x: Reg, y: Reg) {
let src: Reg = if self.flags.quirks.shift { x } else { y };
let shift_out = self.v[src] & 1;
self.v[x] = self.v[src] >> 1;
self.v[0xf] = shift_out;
}
/// |`8xy7`| Performs subtraction of vY and vX, and stores the result in vX
#[inline(always)]
pub(super) fn backwards_sub(&mut self, x: Reg, y: Reg) {
let carry;
(self.v[x], carry) = self.v[y].overflowing_sub(self.v[x]);
self.v[0xf] = (!carry).into();
}
/// 8X_E: Performs bitwise left shift of vX
///
/// # Quirk
/// On the original chip-8 interpreter, this would perform the operation on vY
/// and store the result in vX. This behavior was left out, for now.
#[inline(always)]
pub(super) fn shift_left(&mut self, x: Reg, y: Reg) {
let src: Reg = if self.flags.quirks.shift { x } else { y };
let shift_out: u8 = self.v[src] >> 7;
self.v[x] = self.v[src] << 1;
self.v[0xf] = shift_out;
}
}
// |`9xyn`| Performs a register-register comparison
//
// |opcode| effect |
// |------|------------------------------------|
// |`9XY0`| Skip next instruction if vX != vY |
impl CPU {
/// |`9xy0`| Skip next instruction if X != y
#[inline(always)]
pub(super) fn skip_not_equals(&mut self, x: Reg, y: Reg) {
if self.v[x] != self.v[y] {
self.pc = self.pc.wrapping_add(2);
}
}
}
// |`Aaaa`| Load address #a into register I
impl CPU {
/// |`Aadr`| Load address #adr into register I
#[inline(always)]
pub(super) fn load_i_immediate(&mut self, a: Adr) {
self.i = a;
}
}
// |`Baaa`| Jump to &adr + v0
impl CPU {
/// |`Badr`| Jump to &adr + v0
///
/// Quirk:
/// On the Super-Chip, this does stupid shit
#[inline(always)]
pub(super) fn jump_indexed(&mut self, a: Adr) {
let reg = if self.flags.quirks.stupid_jumps {
a as usize >> 8
} else {
0
};
self.pc = a.wrapping_add(self.v[reg] as Adr);
}
}
// |`Cxbb`| Stores a random number & the provided byte into vX
impl CPU {
/// |`Cxbb`| Stores a random number & the provided byte into vX
#[inline(always)]
pub(super) fn rand(&mut self, x: Reg, b: u8) {
self.v[x] = random::<u8>() & b;
}
}
// |`Dxyn`| Draws n-byte sprite to the screen at coordinates (vX, vY)
impl CPU {
/// |`Dxyn`| Draws n-byte sprite to the screen at coordinates (vX, vY)
///
/// # Quirk
/// On the original chip-8 interpreter, this will wait for a VBI
#[inline(always)]
pub(super) fn draw(&mut self, x: Reg, y: Reg, n: Nib, bus: &mut Bus) {
if !self.flags.quirks.draw_wait {
self.flags.draw_wait = true;
}
// self.draw_hires handles both hi-res mode and drawing 16x16 sprites
if self.flags.draw_mode || n == 0 {
self.draw_hires(x, y, n, bus);
} else {
self.draw_lores(x, y, n, bus);
}
}
#[inline(always)]
pub(super) fn draw_lores(&mut self, x: Reg, y: Reg, n: Nib, bus: &mut Bus) {
self.draw_sprite(self.v[x] as u16 % 64, self.v[y] as u16 % 32, n, 64, 32, bus);
}
#[inline(always)]
pub(super) fn draw_sprite(&mut self, x: u16, y: u16, n: Nib, w: u16, h: u16, bus: &mut Bus) {
let w_bytes = w / 8;
self.v[0xf] = 0;
if let Some(sprite) = bus.get(self.i as usize..(self.i + n as u16) as usize) {
let sprite = sprite.to_vec();
for (line, &sprite) in sprite.iter().enumerate() {
let line = line as u16;
let sprite = ((sprite as u16) << (8 - (x % 8))).to_be_bytes();
for (addr, &byte) in sprite.iter().enumerate().filter_map(|(idx, byte)| {
let x = (x / 8) + idx as u16;
Some((
if self.flags.quirks.screen_wrap {
((y + line) % h * w_bytes + (x % w_bytes)) % (w_bytes * h)
} else if x < w_bytes {
(y + line) * w_bytes + x
} else {
return None;
} + self.screen,
byte,
))
}) {
let screen: u8 = bus.read(addr);
bus.write(addr, byte ^ screen);
if byte & screen != 0 {
self.v[0xf] = 1;
}
}
}
}
}
}
// |`Exbb`| Skips instruction on value of keypress
//
// |opcode| effect |
// |------|------------------------------------|
// |`eX9e`| Skip next instruction if key == vX |
// |`eXa1`| Skip next instruction if key != vX |
impl CPU {
/// |`Ex9E`| Skip next instruction if key == vX
#[inline(always)]
pub(super) fn skip_key_equals(&mut self, x: Reg) {
if self.keys[self.v[x] as usize & 0xf] {
self.pc += 2;
}
}
/// |`ExaE`| Skip next instruction if key != vX
#[inline(always)]
pub(super) fn skip_key_not_equals(&mut self, x: Reg) {
if !self.keys[self.v[x] as usize & 0xf] {
self.pc += 2;
}
}
}
// |`Fxbb`| Performs IO
//
// |opcode| effect |
// |------|------------------------------------|
// |`fX07`| Set vX to value in delay timer |
// |`fX0a`| Wait for input, store key in vX |
// |`fX15`| Set sound timer to the value in vX |
// |`fX18`| set delay timer to the value in vX |
// |`fX1e`| Add vX to I |
// |`fX29`| Load sprite for character x into I |
// |`fX33`| BCD convert X into I[0..3] |
// |`fX55`| DMA Stor from I to registers 0..=X |
// |`fX65`| DMA Load from I to registers 0..=X |
impl CPU {
/// |`Fx07`| Get the current DT, and put it in vX
/// ```py
/// vX = DT
/// ```
#[inline(always)]
pub(super) fn load_delay_timer(&mut self, x: Reg) {
self.v[x] = self.delay as u8;
}
/// |`Fx0A`| Wait for key, then vX = K
#[inline(always)]
pub(super) fn wait_for_key(&mut self, x: Reg) {
if let Some(key) = self.flags.lastkey {
self.v[x] = key as u8;
self.flags.lastkey = None;
} else {
self.pc = self.pc.wrapping_sub(2);
self.flags.keypause = true;
}
}
/// |`Fx15`| Load vX into DT
/// ```py
/// DT = vX
/// ```
#[inline(always)]
pub(super) fn store_delay_timer(&mut self, x: Reg) {
self.delay = self.v[x] as f64;
}
/// |`Fx18`| Load vX into ST
/// ```py
/// ST = vX;
/// ```
#[inline(always)]
pub(super) fn store_sound_timer(&mut self, x: Reg) {
self.sound = self.v[x] as f64;
}
/// |`Fx1e`| Add vX to I,
/// ```py
/// I += vX;
/// ```
#[inline(always)]
pub(super) fn add_i(&mut self, x: Reg) {
self.i += self.v[x] as u16;
}
/// |`Fx29`| Load sprite for character x into I
/// ```py
/// I = sprite(X);
/// ```
#[inline(always)]
pub(super) fn load_sprite(&mut self, x: Reg) {
self.i = self.font + (5 * (self.v[x] as Adr % 0x10));
}
/// |`Fx33`| BCD convert X into I`[0..3]`
#[inline(always)]
pub(super) fn bcd_convert(&mut self, x: Reg, bus: &mut Bus) {
let x = self.v[x];
bus.write(self.i.wrapping_add(2), x % 10);
bus.write(self.i.wrapping_add(1), x / 10 % 10);
bus.write(self.i, x / 100 % 10);
}
/// |`Fx55`| DMA Stor from I to registers 0..=X
///
/// # Quirk
/// The original chip-8 interpreter uses I to directly index memory,
/// with the side effect of leaving I as I+X+1 after the transfer is done.
#[inline(always)]
pub(super) fn store_dma(&mut self, x: Reg, bus: &mut Bus) {
let i = self.i as usize;
for (reg, value) in bus
.get_mut(i..=i + x)
.unwrap_or_default()
.iter_mut()
.enumerate()
{
*value = self.v[reg]
}
if !self.flags.quirks.dma_inc {
self.i += x as Adr + 1;
}
}
/// |`Fx65`| DMA Load from I to registers 0..=X
///
/// # Quirk
/// The original chip-8 interpreter uses I to directly index memory,
/// with the side effect of leaving I as I+X+1 after the transfer is done.
#[inline(always)]
pub(super) fn load_dma(&mut self, x: Reg, bus: &mut Bus) {
let i = self.i as usize;
for (reg, value) in bus.get(i..=i + x).unwrap_or_default().iter().enumerate() {
self.v[reg] = *value;
}
if !self.flags.quirks.dma_inc {
self.i += x as Adr + 1;
}
}
}
//////////////// SUPER CHIP ////////////////
impl CPU {
/// |`00cN`| Scroll the screen down N lines
#[inline(always)]
pub(super) fn scroll_down(&mut self, n: Nib, bus: &mut Bus) {
match self.flags.draw_mode {
true => {
// Get a line from the bus
for i in (0..16 * (64 - n as usize)).step_by(16).rev() {
let i = i + self.screen as usize;
let line: u128 = bus.read(i);
bus.write(i - (n as usize * 16), 0u128);
bus.write(i, line);
}
}
false => {
// Get a line from the bus
for i in (0..8 * (32 - n as usize)).step_by(8).rev() {
let i = i + self.screen as usize;
let line: u64 = bus.read(i);
bus.write(i, 0u64);
bus.write(i + (n as usize * 8), line);
}
}
}
}
/// |`00fb`| Scroll the screen right
#[inline(always)]
pub(super) fn scroll_right(&mut self, bus: &mut (impl ReadWrite<u128> + ReadWrite<u128>)) {
// Get a line from the bus
for i in (0..16 * 64).step_by(16) {
//let line: u128 = bus.read(self.screen + i) >> 4;
bus.write(self.screen + i, bus.read(self.screen + i) >> 4);
}
}
/// |`00fc`| Scroll the screen right
#[inline(always)]
pub(super) fn scroll_left(&mut self, bus: &mut (impl ReadWrite<u128> + ReadWrite<u128>)) {
// Get a line from the bus
for i in (0..16 * 64).step_by(16) {
let line: u128 = (bus.read(self.screen + i) & !(0xf << 124)) << 4;
bus.write(self.screen + i, line);
}
}
/// |`Dxyn`|
/// Super-Chip extension high-resolution graphics mode
#[inline(always)]
pub(super) fn draw_hires(&mut self, x: Reg, y: Reg, n: Nib, bus: &mut Bus) {
if !self.flags.quirks.draw_wait {
self.flags.draw_wait = true;
}
let (w, h) = match self.flags.draw_mode {
true => (128, 64),
false => (64, 32),
};
let (x, y) = (self.v[x] as u16 % w, self.v[y] as u16 % h);
match n {
0 => self.draw_schip_sprite(x, y, w, bus),
_ => self.draw_sprite(x, y, n, w, h, bus),
}
}
/// Draws a 16x16 Super Chip sprite
#[inline(always)]
pub(super) fn draw_schip_sprite(&mut self, x: u16, y: u16, w: u16, bus: &mut Bus) {
self.v[0xf] = 0;
let w_bytes = w / 8;
if let Some(sprite) = bus.get(self.i as usize..(self.i + 32) as usize) {
let sprite = sprite.to_owned();
for (line, sprite) in sprite.chunks_exact(2).enumerate() {
let sprite = u16::from_be_bytes(
sprite
.try_into()
.expect("Chunks should only return 2 bytes"),
);
let addr = (y + line as u16) * w_bytes + x / 8 + self.screen;
let sprite = (sprite as u32) << (16 - (x % 8));
let screen: u32 = bus.read(addr);
bus.write(addr, screen ^ sprite);
if screen & sprite != 0 {
self.v[0xf] += 1;
}
}
}
}
/// |`Fx30`| (Super-Chip) 16x16 equivalent of Fx29
///
/// TODO: Actually make and import the 16x font
#[inline(always)]
pub(super) fn load_big_sprite(&mut self, x: Reg) {
self.i = self.font + (5 * 8) + (16 * (self.v[x] as Adr % 0x10));
}
/// |`Fx75`| (Super-Chip) Save to "flag registers"
/// I just chuck it in 0x0..0xf. Screw it.
#[inline(always)]
pub(super) fn store_flags(&mut self, x: Reg, bus: &mut Bus) {
// TODO: Save these, maybe
for (reg, value) in bus
.get_mut(0..=x)
.unwrap_or_default()
.iter_mut()
.enumerate()
{
*value = self.v[reg]
}
}
/// |`Fx85`| (Super-Chip) Load from "flag registers"
/// I just chuck it in 0x0..0xf. Screw it.
#[inline(always)]
pub(super) fn load_flags(&mut self, x: Reg, bus: &mut Bus) {
for (reg, value) in bus.get(0..=x).unwrap_or_default().iter().enumerate() {
self.v[reg] = *value;
}
}
/// Initialize lores mode
pub(super) fn init_lores(&mut self, bus: &mut Bus) {
self.flags.draw_mode = false;
let scraddr = self.screen as usize;
bus.set_region(Region::Screen, scraddr..scraddr + 256);
self.clear_screen(bus);
}
/// Initialize hires mode
pub(super) fn init_hires(&mut self, bus: &mut Bus) {
self.flags.draw_mode = true;
let scraddr = self.screen as usize;
bus.set_region(Region::Screen, scraddr..scraddr + 1024);
self.clear_screen(bus);
}
}
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