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