# TCPU
Assembly language interpreter written in pure C. Can execute programs up to 1 MEGABYTE (1048576 bytes) in size!!!

## Building
1. Install [cbuild](https://timerix.ddns.net:3322/Timerix/cbuild.git)
2.  ```sh
    cbuild build_exec_dbg
    ```

## Assembly language
### Instructions
| code | name | arguments | details |
|------|------|-----------|---------|
| 00 | NOP  |           | ignored instruction |
| 01 | PUSH | `dst_register`, `value_size(bytes)`, `value` | push constant value into `dst_register` | 
| 02 | MOV  | `dst_register`, `src_register` | copy value from `src_register` to `dst_register`
| 03 | ADD  | `dst_register`, `src_register` | `dst` += `src` |
| 04 | SUB  | `dst_register`, `src_register` | `dst` -= `src` |
| 05 | MUL  | `dst_register`, `src_register` | `dst` *= `src` |
| 06 | DIV  | `dst_register`, `src_register` | `dst` /= `src` |
| 07 | MOD  | `dst_register`, `src_register` | `dst` %= `src` |
| 08 | SYS  |           | call system function |
| 09 | EXIT |           | stop the program with exit code in `ax` |

### Registers
| code | name | size (bits) |
|------|------|-------------|
| 00 | ax | 32 |
| 01 | bx | 32 |
| 02 | cx | 32 |
| 03 | dx | 32 |

### System functions
To call a system function you need to push values to registers and write `SYS` opcode. The return value of a function will will be avaliable in `ax` after call.
| `ax` | name | `bx` | `cx` | `dx` | details |
|-----------|------|----|----|----|---------|
| 0 | read  | file number | buffer pointer | buffer size | read data from file |
| 1 | write | file number | buffer pointer | buffer size | write data to file |