Vendor-specific¶

The device driver provides bulk, and optionally interrupt or isochronous, transfers for a vendor-defined interface. There is no generic vendor protocol: the device descriptors, request semantics, framing, and host software are part of the product’s protocol.

Device¶

Enable CFG_TUD_VENDOR and add TUD_VENDOR_DESCRIPTOR for the usual pair of bulk endpoints. Buffered mode is the practical default.

Option	Default	What it controls
`CFG_TUD_VENDOR_RX_BUFSIZE` / `CFG_TUD_VENDOR_TX_BUFSIZE`	Device bulk maximum	Software FIFO bytes. Setting either to zero selects direct mode for both directions.
`CFG_TUD_VENDOR_RX_EPSIZE` / `CFG_TUD_VENDOR_TX_EPSIZE`	Device bulk maximum	Bulk endpoint transfer buffer sizes. Each must be at least the endpoint’s `wMaxPacketSize`.
`CFG_TUD_VENDOR_RX_MANUAL_XFER`	`0`	Disables automatic receive arming at open and transfer completion. Use `tud_vendor_n_read_xfer()` to arm reception explicitly; buffered reads and `tud_vendor_n_read_flush()` also attempt to re-arm it.
`CFG_TUD_VENDOR_RX_NEED_ZLP`	`0`	Allows multi-packet receive termination by a zero-length packet; enable only when the custom host protocol sends that terminator. RX transfers then can request up to `CFG_TUD_VENDOR_RX_EPSIZE` (otherwise one packet); make it a multiple of the OUT endpoint’s `wMaxPacketSize`.
`CFG_TUD_VENDOR_EP_INT_OUT` / `CFG_TUD_VENDOR_EP_INT_IN`	`0`	Enables optional direct interrupt endpoints. Their buffer-size options default to 64 bytes.
`CFG_TUD_VENDOR_EP_ISO_OUT` / `CFG_TUD_VENDOR_EP_ISO_IN`	`0`	Enables optional direct isochronous endpoints. They require alternate settings; their buffers default to 64 bytes.
`CFG_TUD_VENDOR_ALT_SETTINGS`	`0`	Enables alternate-setting tracking. It requires direct mode and is required by the optional isochronous endpoints.

Use tud_vendor_available()/tud_vendor_read() for OUT data and tud_vendor_write()/tud_vendor_write_flush() for IN data. In buffered mode, tud_vendor_rx_cb() is only a notification; read the FIFO rather than using its null buffer argument.

For direct transfers, configure zero RX/TX FIFO sizes and follow the ownership rules in vendor_device.h. Optional interrupt, isochronous, and alternate setting support is controlled by CFG_TUD_VENDOR_EP_* and CFG_TUD_VENDOR_ALT_SETTINGS. Interrupt and isochronous OUT endpoints must be explicitly re-armed after their receive callbacks.

API or callback	What it does
`tud_vendor_n_mounted()`	Tests whether an instance has any configured bulk, interrupt, or isochronous endpoint open.
`tud_vendor_n_available()` / `tud_vendor_n_read()`	Reports and removes bulk OUT FIFO bytes in buffered mode.
`tud_vendor_n_write_available()` / `tud_vendor_n_write()`	Reports room and copies as many bulk IN bytes as fit. In direct mode the copy is limited to one endpoint buffer.
`tud_vendor_n_write_flush()`	Starts a short buffered IN transfer and returns the number of bytes submitted.
`tud_vendor_rx_cb()` / `tud_vendor_tx_cb()`	Announces received data or completed output. In direct mode, consume or copy the receive pointer before returning from the callback.
`tud_vendor_n_int_read_xfer()` / `tud_vendor_n_iso_read_xfer()`	Arms one optional OUT transfer; re-arm after each receive callback.
`tud_vendor_n_int_write()` / `tud_vendor_n_iso_write()`	Copies and queues at most one optional endpoint buffer and returns the accepted byte count.
`tud_vendor_n_alt()`	Returns the host-selected alternate setting when support is enabled.

Handle vendor control requests in tud_vendor_control_xfer_cb() and perform the data/status stage with tud_control_xfer() or tud_control_status(). Validate bmRequestType, bRequest, wIndex, wValue, and wLength before accepting a request.

The WebUSB Serial example combines a vendor bulk interface with WebUSB and Microsoft OS 2.0 descriptors.

Host¶

A host cannot interpret an arbitrary vendor interface from its class code. TinyUSB does not currently offer a supported, protocol-neutral tuh_vendor_* application API. For a simple fixed device, enable CFG_TUH_API_EDPT_XFER and use the descriptor/endpoint APIs demonstrated by Host: Bare API. For a reusable protocol, implement a custom host class driver that matches devices by descriptors and VID/PID and owns their enumeration and transfer state.

Define framing, version negotiation, maximum message lengths, timeouts, and error recovery before deploying a vendor protocol. Never cast unvalidated wire data directly to an application structure.