# new Rollup()

Opens the rollup device and initializes the outputs merkle tree.

On riscv64 (inside the Cartesi Machine) the constructor opens the real machine IO device; elsewhere it starts libcmt's mock driver, configured by the `CMT_INPUTS` / `CMT_DEBUG` environment variables (see [Testing on the Host](/cmio/guide/testing)).

## Usage

```ts twoslash
import { Rollup } from '@deroll/cmio';

const rollup = new Rollup();
```

## Behavior

* The device is **exclusive**: while an instance is open, constructing another throws with `error.errno === -16` (`EBUSY`). Call [`close`](/cmio/reference/close) first.
* On the mock, `CMT_INPUTS` is read once, at construction time — set it before creating the instance.

## Errors

| Condition | Error |
| --- | --- |
| Device already open | `RollupError` with `errno: -16` (`EBUSY`) |
| Device unavailable / driver failure | `RollupError` with the negative errno in `errno` and the libcmt call in `syscall` |