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.
- 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
| 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 |
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.
| 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 |
| Imm |
Meaning |
| 0 |
Exit Program |
| 1 |
Print register A as integer |
| 2 |
Print register A as ASCII char |
- Syscalls also do not modify flags
mov b, 3
mov a, 1
loop:
sub b, a
jnz loop
sys 1 ; print register A
sys 0 ; exit
cargo run -- --f <examples/filename.asc>
- No pipelining
- No interrupts
- No virtual memory
- No privilege levels
- No hardware I/O
- [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
