# TCPU
Machine code 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. Install [SDL3](https://github.com/libsdl-org/SDL) and [SDL3_image](https://github.com/libsdl-org/SDL_image) from package manager or source.
3.  ```sh
    cbuild build_exec_dbg
    ```

## Assembly language
### Registers
| name | code | size (bits) |
|-----|------|----|
| rax | 0x01 | 64 |
| eax | 0x02 | 32 |
| ax  | 0x04 | 16 |
| al  | 0x07 | 8  |
| ah  | 0x08 | 8  |
|                 |
| rbx | 0x11 | 64 |
| ebx | 0x12 | 32 |
| bx  | 0x14 | 16 |
| bl  | 0x17 | 8  |
| bh  | 0x18 | 8  |
|                 |
| rcx | 0x21 | 64 |
| ecx | 0x22 | 32 |
| cx  | 0x24 | 16 |
| cl  | 0x27 | 8  |
| ch  | 0x28 | 8  |
|                 |
| rdx | 0x31 | 64 |
| edx | 0x32 | 32 |
| dx  | 0x34 | 16 |
| dl  | 0x37 | 8  |
| dh  | 0x38 | 8  |

### Instructions
| name | arguments | details |
|------|-----------|---------|
| NOP  |           | ignored instruction |
| EXIT |           | stop the program with exit code in `eax` |
| SYS  |           | call system function |
|                            |
| MOVC | `dst_register`, `const_value` | push constant value into `dst_register` | 
| MOVR | `dst_register`, `src_register` | copy value from `src_register` to `dst_register` |
|                            |
| ADD | `dst_register`, `src_register` | `dst += src` |
| SUB | `dst_register`, `src_register` | `dst -= src` |
| MUL | `dst_register`, `src_register` | `dst *= src` |
| DIV | `dst_register`, `src_register` | `dst /= src` |
| MOD | `dst_register`, `src_register` | `dst %= src` |
|                            |
| EQ | `dst_register`, `src_register` | `cmp_flag = dst == src` |
| NE | `dst_register`, `src_register` | `cmp_flag = dst != src` |
| LT | `dst_register`, `src_register` | `cmp_flag = dst <  src` |
| LE | `dst_register`, `src_register` | `cmp_flag = dst <= src` |
| GT | `dst_register`, `src_register` | `cmp_flag = dst >  src` |
| GE | `dst_register`, `src_register` | `cmp_flag = dst >= src` |
|                            |
| NOT | `dst_register` | `dst = !dst` |
| INV | `dst_register` | `dst = ~dst` |
| OR  | `dst_register`, `src_register` | `dst = dst \| src` |
| XOR | `dst_register`, `src_register` | `dst = dst ^ src` |
| AND | `dst_register`, `src_register` | `dst = dst & src` |
|                            |
| JMP | `dst_address_const` | goto `dst` |
| JNZ | `dst_address_const` | if (`cmp_flag` != 0) goto `dst` |
| JZ  | `dst_address_const` | if (`cmp_flag` == 0) goto `dst` |

### 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.
| name | `al` | `ah` | `rbx` | `ecx` | details |
|------|------|------|-------|-------|---------|
| read  | 0 | file number | buffer pointer | buffer size | read data from file |
| write | 1 | file number | buffer pointer | buffer size | write data to file |