# Terminal interrupts (ivss)

**Terminal interrupts** notify a program when the host terminal supplies an input byte. Start the input thread with:

```bash
$ ./emulator -terminal program.hex
```

For ordinary input, the terminal callback stores the byte in `Emu_TermBuffer` and raises a request under the emulator mutex:

```c
Emu_MutexLock();
INT[INT_TERMINAL] = 1;
Emu_MutexUnlock();
```

The callback first disables canonical input and echo on the host terminal. It has special handling for backtick, which prints registers, and Escape, which stops emulation; these are not ordinary guest input events.

Delivery requires an installed handler and clear terminal and global mask bits. The emulator writes cause three, allowing a shared handler to distinguish terminal input from timer or software events.

The handler reads the [[ivss-terminal-input|input register]] at `0xFFFFFF04`. Storage is a latest-byte buffer rather than an input queue, so slow handling can lose intermediate characters. Restoring registers and using `iret` returns to the interrupted program with its saved status.

Source: [emulator.c](https://github.com/yanevskiv/ivss/blob/main/src/emulator.c).