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The TXT-8 is a simple 8-bit virtual machine based on the command line.
TXT-8 has a minimal instruction set which demonstrates the fundamental aspects of virtualization.
I originally created TXT-8 to provide digestible substance for my lecture on virtualization for the programming club at my school.
Components and specifications of TXT-8.
- 8x 8-bit general-purpose registers.
- 8-level 12-bit address stack.
- 12-bit stack pointer.
- 12-bit program counter.
- 12-bit index register.
- 4096 bytes of memory (4KB).
- 12-bit addressing.
- 8-bit output buffer.
- 8-bit buffer pointer that points to the end of the buffer.
A: 8-bit register (4 bytes).
B: 8-bit register (4 bytes).
ADDR: 12-bit address (12 bytes).
| Opcode | Mnemonic | Operands | Description |
|---|---|---|---|
| 0 | CALL | ADDR | Call subroutine |
| 1 | RET | NULL | Return from subroutine |
| 2 | JMP | ADDR | Jump to address |
| 3 | ADD | X, Y | Add X and Y (store in X) |
| 4 | SUB | X, Y | Subtract Y from X (store in X) |
| 5 | AND | X, Y | AND X and Y (store in X) |
| 6 | OR | X, Y | OR X and Y (store in X) |
| 7 | XOR | X, Y | XOR X and Y (store in X) |
| 8 | SHR | X, Y | Shift X right by Y (store in X) |
| 9 | SHL | X, Y | Shift X left by Y (store in X) |
| A | LDB | X | Load output buffer with value of register X. Y bit low enables ASCII encoding. |
| B | LDI | X, BYTE | Load immediate value into X |
| C | LDR | X, Y | Load value of Y into X |
| D | LDX | ADRR | Load index register with address |
| E | STR | X | Load value of X into memory[index] |
| F | PRNT | NULL | Print the text buffer and clear its contents |
A Makefile is provided in the root directory that can be used to build/clean the project.
Simply run make build to compile the project.
./bin/txt8 <path-to-program>
Examples can be found in the examples folder.
You can make your own programs by manually typing the instructions into a hex editor. I plan on making an assembler (so you can use ASM rather than manual hexadecimal) for TXT-8 once I finish fleshing out the instruction set.
The .t8 extension for programs is not necessary, but I recommend it for clarity.
TXT-8 - Apache 2.9