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# Software interrupts (ivss)

A **software interrupt** is requested by the program through `int`. This complete example installs a handler, requests an interrupt, and resumes at `halt`:

```asm
.section my_code
    ld $handler, %r1
    csrwr %r1, %handler
    int
    halt
handler:
    ld $42, %r5
    iret
.end
```

The emulator sets a pending software flag when it executes `int`. Its following interrupt check builds the frame, writes cause four, and transfers to the installed handler. The handler leaves forty-two in `%r5`; `iret` restores the saved state and returns to the instruction following `int`.

Software delivery does not require `-timer` or `-terminal`. Those options enable host-generated device events, not the program's own request.

In this implementation the software case does not consult the timer, terminal, or global hardware-mask bits. Do not assume that setting the global status mask blocks every interrupt kind. The handler and internal interrupt-enable checks still apply to delivery.

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