mirror of https://github.com/mre/mos6502.git
125 lines
3.8 KiB
Markdown
125 lines
3.8 KiB
Markdown
# mos6502
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[](https://docs.rs/mos6502)
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An emulator for the [MOS 6502 CPU](https://en.wikipedia.org/wiki/MOS_Technology_6502) written in Rust.
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Tested and validated by [solid65](https://github.com/omarandlorraine/solid65).
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It builds on stable Rust and supports `#[no_std]` targets.
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## What is the MOS 6502?
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> The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") is an 8-bit microprocessor that was designed by a small team led by Chuck Peddle for MOS Technology. [...]
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>
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> When it was introduced in 1975, the 6502 was the **least expensive microprocessor on the market** by a considerable margin. It initially sold for less than one-sixth the cost of competing designs from larger companies, such as the 6800 or Intel 8080. Its introduction caused rapid decreases in pricing across the entire processor market. **Along with the Zilog Z80, it sparked a series of projects that resulted in the home computer revolution of the early 1980s.**
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Source: [Wikipedia](https://en.wikipedia.org/wiki/MOS_Technology_6502)
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## How to use this library
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```rust
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use mos6502::memory::Bus;
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use mos6502::memory::Memory;
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use mos6502::instruction::Nmos6502;
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use mos6502::cpu;
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fn main() {
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// Calculate the greatest common divisor of 56 and 49
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// using Euclid's algorithm.
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let zero_page_data = [56, 49];
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let program = [
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// (F)irst | (S)econd
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// .algo
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0xa5, 0x00, // Load from F to A
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// .algo_
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0x38, // Set carry flag
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0xe5, 0x01, // Substract S from number in A (from F)
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0xf0, 0x07, // Jump to .end if diff is zero
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0x30, 0x08, // Jump to .swap if diff is negative
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0x85, 0x00, // Load A to F
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0x4c, 0x12, 0x00, // Jump to .algo_
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// .end
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0xa5, 0x00, // Load from S to A
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0xff,
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// .swap
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0xa6, 0x00, // load F to X
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0xa4, 0x01, // load S to Y
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0x86, 0x01, // Store X to F
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0x84, 0x00, // Store Y to S
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0x4c, 0x10, 0x00, // Jump to .algo
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];
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let mut cpu = cpu::CPU::new(Memory::new(), Nmos6502);
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cpu.memory.set_bytes(0x00, &zero_page_data);
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cpu.memory.set_bytes(0x10, &program);
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cpu.registers.program_counter = 0x10;
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cpu.run();
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// The expected GCD is 7
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assert_eq!(7, cpu.registers.accumulator);
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}
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```
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The same can be achieved, by compiling the euclid example yourself.
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First install a 6502 assembler and linker, e.g. [cc65](https://cc65.github.io/cc65/).
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```sh
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brew install cc65
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```
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Then compile and link the assembly file:
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```sh
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cd examples/asm/euclid
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ca65 euclid.a65
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ld65 -C ../linker.cfg -o euclid.bin euclid.o
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```
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This will create a binary file `euclid.bin` that you can load into the emulator:
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```rust
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use mos6502::memory::Bus;
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use mos6502::memory::Memory;
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use mos6502::instruction::Nmos6502;
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use mos6502::cpu;
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use std::fs::read;
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fn main() {
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// Calculate the greatest common divisor of 56 and 49
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// using Euclid's algorithm.
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let zero_page_data = [56, 49];
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// Load the binary file from disk
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let program = match read("examples/asm/euclid/euclid.bin") {
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Ok(data) => data,
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Err(err) => {
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println!("Error reading euclid.bin: {}", err);
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return;
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}
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};
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let mut cpu = cpu::CPU::new(Memory::new(), Nmos6502);
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cpu.memory.set_bytes(0x00, &zero_page_data);
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cpu.memory.set_bytes(0x10, &program);
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cpu.registers.program_counter = 0x10;
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cpu.run();
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// The expected GCD is 7
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assert_eq!(7, cpu.registers.accumulator);
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}
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```
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## Credits
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This started off as a fork of [amw-zero/6502-rs](https://github.com/amw-zero/6502-rs),
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which seems to be [unmaintained](https://github.com/amw-zero/6502-rs/pull/36) at this point.
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