114 lines
2.7 KiB
Markdown
114 lines
2.7 KiB
Markdown
# 8-Bit CPU Emulator
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This project is an educational 8-bit CPU emulator written in Rust, it's build to understand core computer architecture concepts such as instruction sets, flags,
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control flow, stacks and system calls.
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This project is **not** a production CPU and **not** accurate. It is designed purely for learning and experimentation.
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-----
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## Features
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- Custom 8-bit ISA (control-flow and arithmetic operations)
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- 4 general-purpose registers
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- 64 KB (0x0000-0xFFFF) byte-addressable memory
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- Two-pass assembler with label support
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- Stack-based function calls
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- Stack is software-managed and grows downward
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---
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## Registers
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| Register | Size | Description |
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| -------- | ------ | ------------------------------ |
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| A | 8-bit | General-purpose register |
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| B | 8-bit | General-purpose register |
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| C | 8-bit | General-purpose register |
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| D | 8-bit | General-purpose register |
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| PC | 16-bit | Program Counter |
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| SP | 16-bit | Stack pointer |
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## Flags Register
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The CPU maintains a small flags register.
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| Flag | Description |
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| ----- | ------------ |
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| Z | Zero flag - set if last result was `0` |
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| C | Carry/Borrow flag |
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- Control-flow instructions do **not** modify flags.
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## Supported Instructions
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| Instruction | Syntax |
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| ----------- | ---------------- |
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| MOV | mov dest, src OR mov reg, imm |
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| ADD | add r1, r2 OR add reg, imm |
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| SUB | sub r1, r2 OR sub reg, imm |
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| JMP | jmp addr OR jmp addr |
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| JZ | jz addr OR jz addr |
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| JNZ | jnz addr OR jnz addr |
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| CMP | cmp r1, r2 OR cmp reg, imp |
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| MUL | mul r1, r2 |
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| DIV | div r1, r2 |
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| CALL | call \<label\> |
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| SYS | sys \<syscall_no\> |
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| HLT (Halt) | hlt |
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## Syscalls
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| Imm | Meaning |
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| --- | ------- |
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| 0 | Exit Program |
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| 1 | Print register A as integer |
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| 2 | Print register A as ASCII char |
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- Syscalls also do not modify flags
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## Example assembly program
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```assembly
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mov b, 3
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mov a, 1
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loop:
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sub b, a
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jnz loop
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sys 1 ; print register A
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sys 0 ; exit
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```
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## Usage
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```bash
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cargo run -- --f <examples/filename.asc>
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```
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## Non-goals
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1. No pipelining
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2. No interrupts
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3. No virtual memory
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4. No privilege levels
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5. No hardware I/O
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## Goals
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- [x] Assembler
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- [x] Lexer/Tokenizer
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- [x] Add label support (supporting JMP/JZ/JNZ)
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- [x] Add instructions
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- [x] CMP
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- [x] MUL
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- [x] DIV
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- [x] CALL
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- [x] RET
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- [x] SYS
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- [ ] Better error-handling
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- [ ] TUI debugger
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