mirror of
https://github.com/mre/mos6502.git
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188 lines
5.6 KiB
Rust
188 lines
5.6 KiB
Rust
// Copyright (C) 2014 The 6502-rs Developers
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions
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// are met:
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// 1. Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright
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// notice, this list of conditions and the following disclaimer in the
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// documentation and/or other materials provided with the distribution.
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// 3. Neither the names of the copyright holders nor the names of any
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// contributors may be used to endorse or promote products derived from this
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// software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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// POSSIBILITY OF SUCH DAMAGE.
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use address::{Address, AddressDiff};
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use memory::{STACK_ADDRESS_LO, STACK_ADDRESS_HI};
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// Useful for constructing Status instances
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#[derive(Copy, Clone)]
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pub struct StatusArgs {
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pub negative: bool,
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pub overflow: bool,
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pub unused: bool,
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pub brk: bool,
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pub decimal_mode: bool,
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pub disable_interrupts: bool,
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pub zero: bool,
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pub carry: bool,
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}
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impl StatusArgs {
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pub fn none() -> StatusArgs {
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StatusArgs {
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negative: false,
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overflow: false,
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unused: false,
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brk: false,
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decimal_mode: false,
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disable_interrupts: false,
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zero: false,
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carry: false,
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}
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}
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}
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bitflags! {
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pub struct Status: u8 {
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const PS_NEGATIVE = 0b1000_0000;
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const PS_OVERFLOW = 0b0100_0000;
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const PS_UNUSED = 0b0010_0000; // JAM: Should this exist?
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// (note that it affects the
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// behavior of things like
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// from_bits_truncate)
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const PS_BRK = 0b0001_0000;
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const PS_DECIMAL_MODE = 0b0000_1000;
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const PS_DISABLE_INTERRUPTS = 0b0000_0100;
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const PS_ZERO = 0b0000_0010;
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const PS_CARRY = 0b0000_0001;
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}
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}
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impl Status {
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pub fn default() -> Status {
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// TODO akeeton: Revisit these defaults.
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Status::new(StatusArgs {
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negative: false,
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overflow: false,
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unused: true,
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brk: false,
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decimal_mode: false,
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disable_interrupts: true,
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zero: false,
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carry: false,
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})
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}
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pub fn new(StatusArgs { negative,
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overflow,
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unused,
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brk,
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decimal_mode,
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disable_interrupts,
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zero,
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carry }: StatusArgs) -> Status
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{
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let mut out = Status::empty();
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if negative {
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out = out | PS_NEGATIVE
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}
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if overflow {
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out = out | PS_OVERFLOW
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}
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if unused {
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out = out | PS_UNUSED
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}
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if brk {
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out = out | PS_BRK
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}
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if decimal_mode {
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out = out | PS_DECIMAL_MODE
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}
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if disable_interrupts {
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out = out | PS_DISABLE_INTERRUPTS
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}
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if zero {
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out = out | PS_ZERO
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}
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if carry {
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out = out | PS_CARRY
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}
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out
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}
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pub fn and(&mut self, rhs: Status) {
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*self = *self & rhs;
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}
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pub fn or(&mut self, rhs: Status) {
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*self = *self | rhs;
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}
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pub fn set_with_mask(&mut self, mask: Status, rhs: Status) {
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*self = (*self & !mask) | rhs;
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}
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}
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#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
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pub struct StackPointer(pub u8);
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impl StackPointer {
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pub fn to_address(&self) -> Address {
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let StackPointer(sp) = *self;
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STACK_ADDRESS_LO + AddressDiff(sp as i32)
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}
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// JAM: FIXME: Should we prevent overflow here? What would a 6502 do?
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pub fn decrement(&mut self) {
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let StackPointer(val) = *self;
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*self = StackPointer(val - 1);
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}
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pub fn increment(&mut self) {
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let StackPointer(val) = *self;
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*self = StackPointer(val + 1);
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}
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}
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#[derive(Copy, Clone, PartialEq, Eq, Debug)]
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pub struct Registers {
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pub accumulator: i8,
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pub index_x: i8,
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pub index_y: i8,
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pub stack_pointer: StackPointer,
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pub program_counter: Address,
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pub status: Status,
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}
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impl Registers {
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pub fn new() -> Registers {
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// TODO akeeton: Revisit these defaults.
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Registers {
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accumulator: 0,
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index_x: 0,
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index_y: 0,
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stack_pointer: StackPointer(STACK_ADDRESS_HI.get_offset()),
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program_counter: Address(0),
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status: Status::default(),
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}
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}
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}
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