# Control transfers _Run a control request against the real device, read its answer_ `transfer` runs one USB control transfer against the real device on the host chip and returns its answer as a [`TransferOutcome`](/library/types/structs.md#transfer-outcome). It rides its own inter-chip link pair, not the game PC's EP0 proxy, and is single-outstanding. Read a descriptor, string, or vendor value straight from the device. ``` native device the box (host chip | device chip = the clone) game PC HID report ---IN---> [ HID_IN ]--> renderer --> [ EMIT ]---interrupt-IN---> reads report relayed <--OUT--- [ HID_OUT ]<-- relay <---------------- interrupt-OUT <-- writes report control <-- EP0 -> [ CONTROL ]<-- proxy ------------------- EP0 <--------> GET_DESCRIPTOR, SET_* ^ +-- transfer(ep, setup) <== your own control request, its own link pair ``` > **Warning** > > The advanced control layer is gated on the imperfect-clone opt-in. With [`allow_imperfect_clones`](/library/options.md#allow-imperfect-clones) off, the box answers `Refused` rather than reaching the device. ## transfer _One control transfer, blocking on the answer_ ```text fn transfer(&self, ep: u8, setup: Setup, out: &[u8]) -> Result ``` ```text fn transfer_timeout(&self, ep: u8, setup: Setup, out: &[u8], timeout: Duration) -> Result ``` _Blocks_ | Parameter | Type | Description | | --- | --- | --- | | `ep` | `u8` | `0` for EP0, or a control endpoint number the device declares. | | `setup` | [`Setup`](/library/types/structs.md#setup) | The eight-byte setup packet. | | `out` | `&[u8]` | The OUT data stage: the bytes carried after the setup packet. Empty for an IN transfer. | `Ok(_)` means the box answered at all: a [`TransferStatus`](/library/types/enums.md#transfer-status) other than `Ok` comes back inside the [`TransferOutcome`](/library/types/structs.md#transfer-outcome), not as an error. > **Note** > > `transfer` uses `DEFAULT_TRANSFER_TIMEOUT` (1.5 s). The box gives up after its own ~800 ms window; keep `transfer_timeout` at or above that. #### EXAMPLE ```rust use medius::{Device, Setup, TransferStatus}; let device = Device::find()?; device.allow_imperfect_clones(true)?; let reply = device.transfer(0, Setup::new(0x80, 0x06, 0x0100, 0x0000, 18), &[])?; if reply.status == TransferStatus::Ok { println!("device descriptor: {:02x?}", reply.data()); } ``` ## On AsyncDevice _transfer awaits the device's answer_ [`AsyncDevice`](/library/features/async.md) makes `transfer` and `transfer_timeout` futures, awaited like any query, since each waits for the device's answer. #### EXAMPLE ```rust use futures::executor::block_on; use medius::{AsyncDevice, Setup, TransferStatus}; let device = AsyncDevice::open("/dev/ttyACM0")?; device.allow_imperfect_clones(true)?; let reply = block_on(device.transfer(0, Setup::new(0x80, 0x06, 0x0100, 0x0000, 18), &[]))?; if reply.status == TransferStatus::Ok { println!("device descriptor: {:02x?}", reply.data()); } ```