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USB(4) Device Drivers Manual USB(4)

usb, uhubintroduction to Universal Serial Bus support

# octeon specific
dwctwo0 at iobus? irq 56
# all architectures
ehci* at cardbus?
ohci* at cardbus?
uhci* at cardbus?
ehci* at pci?
ohci* at pci?
uhci* at pci?
xhci* at pci?
usb* at dwctwo?
usb* at ehci? flags 0x00
usb* at ohci? flags 0x00
usb* at uhci? flags 0x00
usb* at xhci? flags 0x00
uhub* at usb?
uhub* at uhub?


#include <dev/usb/usb.h>
#include <dev/usb/usbhid.h>

OpenBSD provides machine-independent bus support and drivers for Universal Serial Bus (USB) devices.

The OpenBSD usb driver has three layers (like scsi(4) and pcmcia(4)): the controller, the bus, and the device layer. The controller attaches to a physical bus (like pci(4) or cardbus(4)). The USB bus attaches to the controller and the root hub attaches to the USB bus. Devices, which may include further hubs, attach to the root hub. The attachment forms the same tree structure as the physical USB device tree. For each USB device there may be additional drivers attached to it.

The uhub driver controls USB hubs and must always be present since there is at least one root hub in any USB system.

The flags are used to specify if the devices on the USB bus should be probed early in the boot process. If the flags are specified with a value of 1, the USB bus will be probed when the USB host device is attached instead of waiting until kernel processes start running.

OpenBSD provides support for the following devices. Note that not all architectures support all devices.

USB Mass Storage Devices, e.g., external disk drives

ADMtek AN986/ADM8511 Pegasus family 10/100 USB Ethernet device
ASIX Electronics AX88172/AX88178/AX88772 10/100/Gigabit USB Ethernet device
ASIX Electronics AX88179 10/100/Gigabit USB Ethernet device
USB Communication Device Class Ethernet device
CATC USB-EL1201A USB Ethernet device
Kawasaki LSI KL5KUSB101B USB Ethernet device
MosChip MCS7730/7830/7832 10/100 USB Ethernet device
Microchip LAN75xx/LAN78xx 10/100/Gigabit USB Ethernet device
SMSC LAN95xx 10/100 USB Ethernet device
Davicom DM9601 10/100 USB Ethernet device
RealTek RTL8152/RTL8153 10/100/Gigabit USB Ethernet device
Realtek RTL8150L 10/100 USB Ethernet device
USB Remote NDIS Ethernet device

Atheros IEEE 802.11a/b/g/n wireless network device
Atmel AT76C50x IEEE 802.11b wireless network device
Broadcom and Cypress IEEE 802.11a/ac/b/g/n wireless network device
Atheros USB IEEE 802.11a/b/g/n wireless network device
Realtek RTL8188SU/RTL8192SU USB IEEE 802.11b/g/n wireless network device
Ralink Technology/MediaTek USB IEEE 802.11a/b/g wireless network device
Ralink Technology/MediaTek USB IEEE 802.11a/b/g/n wireless network device
Atheros USB IEEE 802.11a/b/g wireless network device
Conexant/Intersil PrismGT SoftMAC USB IEEE 802.11b/g wireless network device
Ralink Technology/MediaTek USB IEEE 802.11b/g wireless network device
Realtek RTL8187L/RTL8187B USB IEEE 802.11b/g wireless network device
Realtek RTL8188CU/RTL8188EU/RTL8192CU/RTL8192EU USB IEEE 802.11b/g/n wireless network device
Intersil PRISM 2-3 IEEE 802.11b wireless network device
ZyDAS ZD1211/ZD1211B USB IEEE 802.11b/g wireless network device

MosChip Semiconductor MCS7703 based USB serial adapter
Arkmicro Technologies ARK3116 based USB serial adapter
Belkin USB serial adapter
WinChipHead CH341/340 based USB serial adapter
USB tty support
Cypress microcontroller based USB serial adapter
FTDI USB serial adapter
iPAQ USB units
USB printer support
MosChip Semiconductor based USB multiport serial adapter
MCT USB-RS232 USB serial adapter
USB modem support
Qualcomm MSM modem device
Prolific PL-2303 USB serial adapter
simple USB serial adapters
Silicon Laboratories CP210x based USB serial adapter
Silicon Laboratories CP2110 based USB serial adapter
Texas Instruments TUSB3410 USB serial adapter
USB Handspring Visor
SUNTAC Slipper U VS-10U USB serial adapter
Exar XR21V1410 USB serial adapter

USB audio devices
USB MIDI devices

DisplayLink DL-120 / DL-160 USB display devices
USB Fushicai USBTV007 audio/video capture device
USB video devices

Gude ADS Expert mouseCLOCK USB timedelta sensor
Meinberg Funkuhren USB5131 timedelta sensor

D-Link DSB-R100 USB radio device

Broadcom trackpad mouse
Generic driver for Human Interface Devices
Base driver for all Human Interface Devices
USB keyboards that follow the boot protocol
USB HID mouse, touchscreen and digitiser devices
USB HID multitouch touchpad devices
Toradex OAK USB illuminance sensor
Toradex OAK USB temperature and relative humidity sensor
Toradex OAK USB +/-10V 8channel ADC interface
USB Power Devices sensor
TEMPer HID thermometer and hygrometer
Apple touchpad mouse
USBRH temperature and humidity sensor
YUREX USB twitch/jiggle of knee sensor
Wacom USB tablets

USB Mobile Broadband Interface Model (MBIM)

Research In Motion BlackBerry
USB generic device support
Genesys Logic based host-to-host adapters
TEMPer gold HID thermometer and hygrometer
Moonbase Otago OneRNG TRNG
Maxim/Dallas DS2490 USB 1-Wire adapter
Prolific based host-to-host adapters
USB Random Number Generator devices
USPS composite AC power and temperature sensor
USB touchscreen support

There are different versions of the USB which provide different speeds. USB 3 can operate up to 5.0Gb/s. USB 2 operates at 480Mb/s, while USB versions 1 and 1.1 operate at 12 Mb/s and 1.5 Mb/s for low speed devices. Each USB has a host controller that is the master of the bus; all other devices on the bus only speak when spoken to.

There can be up to 127 devices (apart from the host controller) on a bus, each with its own address. The addresses are assigned dynamically by the host when each device is attached to the bus.

Within each device there can be up to 16 endpoints. Each endpoint is individually addressed and the addresses are static. Each of these endpoints will communicate in one of four different modes: control, isochronous, bulk, or interrupt. A device always has at least one endpoint. This is a control endpoint at address 0 and is used to give commands to the device and extract basic data, such as descriptors, from the device. Each endpoint, except the control endpoint, is unidirectional.

The endpoints in a device are grouped into interfaces. An interface is a logical unit within a device; e.g., a compound device with both a keyboard and a trackball would present one interface for each. An interface can sometimes be set into different modes, called alternate settings, which affects how it operates. Different alternate settings can have different endpoints within it.

A device may operate in different configurations. Depending on the configuration the device may present different sets of endpoints and interfaces.

Each device located on a hub has several config(8) locators:

Number of the port on closest upstream hub.
Configuration the device must be in for this driver to attach. This locator does not set the configuration; it is iterated by the bus enumeration.
Interface number within a device that an interface driver attaches to.
16-bit vendor ID of the device.
16-bit product ID of the device.
16-bit release (revision) number of the device.

The first locator can be used to pin down a particular device according to its physical position in the device tree. The last three locators can be used to pin down a particular device according to what device it actually is.

The bus enumeration of the USB bus proceeds in several steps:

  1. Any device-specific driver can attach to the device.
  2. If none is found, any device class specific driver can attach.
  3. If none is found, all configurations are iterated over. For each configuration all the interfaces are iterated over and interface drivers can attach. If any interface driver attached in a certain configuration, the iteration over configurations is stopped.
  4. If still no drivers have been found, the generic USB driver can attach.

Use the following to get access to the USB specific structures and defines:

#include <dev/usb/usb.h>

The /dev/usbN device can be opened and a few operations can be performed on it. The following ioctl(2) commands are supported on the controller device:

struct usb_device_info
This command can be used to retrieve some information about a device on the bus. The udi_addr field should be filled before the call and the other fields will be filled by information about the device on that address. Should no such device exist, an error is reported.
struct usb_device_info {
	u_int8_t	udi_bus;
	u_int8_t	udi_addr;	/* device address */
	char		udi_product[USB_MAX_STRING_LEN];
	char		udi_vendor[USB_MAX_STRING_LEN];
	char		udi_release[8];
	u_int16_t	udi_productNo;
	u_int16_t	udi_vendorNo;
	u_int16_t	udi_releaseNo;
	u_int8_t	udi_class;
	u_int8_t	udi_subclass;
	u_int8_t	udi_protocol;
	u_int8_t	udi_config;
	u_int8_t	udi_speed;
#define USB_SPEED_LOW  1
#define USB_SPEED_FULL 2
#define USB_SPEED_HIGH 3
	int		udi_power;	/* power consumption */
	int		udi_nports;
	char		udi_devnames[USB_MAX_DEVNAMES]
	u_int8_t	udi_ports[16];	/* hub only */
#define USB_PORT_ENABLED 0xff
#define USB_PORT_POWERED 0xfd
#define USB_PORT_DISABLED 0xfc
	char		udi_serial[USB_MAX_STRING_LEN];

The udi_bus field contains the device unit number of the device.

The udi_product, udi_vendor, and udi_release fields contain self-explanatory descriptions of the device. The udi_productNo, udi_vendorNo, and udi_releaseNo fields contain numeric identifiers for the device.

The udi_class and udi_subclass fields contain the device class and subclass.

The udi_config field shows the current configuration of the device.

The udi_protocol field contains the device protocol as given from the device.

The udi_speed field contains the speed of the device.

The udi_power field shows the power consumption in milli-amps drawn at 5 volts or is zero if the device is self powered.

The udi_devnames field contains the names and instance numbers of the device drivers for the devices attached to this device.

If the device is a hub, the udi_nports field is non-zero and the udi_ports field contains the addresses of the connected devices. If no device is connected to a port, one of the USB_PORT_* values indicates its status.

struct usb_device_stats
This command retrieves statistics about the controller.
struct usb_device_stats {
	u_long	uds_requests[4];

The uds_requests field is indexed by the transfer kind, i.e. UE_*, and indicates how many transfers of each kind have been completed by the controller.

struct usb_device_ddesc
This command can be used to retrieve the device descriptor of a device on the bus. The udd_addr field needs to be filled with the bus device address:
struct usb_device_ddesc {
	u_int8_t	udd_bus;
	u_int8_t	udd_addr;	/* device address */
	usb_device_descriptor_t udd_desc;

The udd_bus field contains the device unit number.

The udd_desc field contains the device descriptor structure.

struct usb_device_cdesc
This command can be used to retrieve the configuration descriptor for the given configuration of a device on the bus. The udc_addr field needs to be filled with the bus device address. The udc_config_index field needs to be filled with the configuration index for the relevant configuration descriptor. For convenience the current configuration can be specified by USB_CURRENT_CONFIG_INDEX:
struct usb_device_cdesc {
	u_int8_t	udc_bus;
	u_int8_t	udc_addr;	/* device address */
	int		udc_config_index;
	usb_config_descriptor_t udc_desc;

The udc_bus field contains the device unit number.

The udc_desc field contains the configuration descriptor structure.

struct usb_device_fdesc
This command can be used to retrieve all descriptors for the given configuration of a device on the bus. The udf_addr field needs to be filled with the bus device address. The udf_config_index field needs to be filled with the configuration index for the relevant configuration descriptor. For convenience the current configuration can be specified by USB_CURRENT_CONFIG_INDEX. The udf_data field needs to point to a memory area of the size given in the udf_size field. The proper size can be determined by first issuing a USB_DEVICE_GET_CDESC command and inspecting the wTotalLength field:
struct usb_device_fdesc {
	u_int8_t	 udf_bus;
	u_int8_t	 udf_addr;	/* device address */
	int		 udf_config_index;
	u_int		 udf_size;
	u_char		*udf_data;

The udf_bus field contains the device unit number.

The udf_data field contains all descriptors.

struct usb_ctl_request
This command can be used to execute arbitrary requests on the control pipe. This is and should be used with great care since it can destroy the bus integrity.

The usb_ctl_request structure has the following definition:

typedef struct {
        uByte           bmRequestType;
        uByte           bRequest;
        uWord           wValue;
        uWord           wIndex;
        uWord           wLength;
} __packed usb_device_request_t;

struct usb_ctl_request {
	int	ucr_addr;
	usb_device_request_t ucr_request;
	void	*ucr_data;
	int	ucr_flags;
#define USBD_SHORT_XFER_OK 0x04	/* allow short reads */
	int	ucr_actlen;	/* actual length transferred */

The ucr_addr field identifies the device on which to perform the request. The ucr_request field identifies parameters of the request, such as length and type. The ucr_data field contains the location where data will be read from or written to. The ucr_flags field specifies options for the request, and the ucr_actlen field contains the actual length transferred as the result of the request.

The include file <dev/usb/usb.h> contains definitions for the types used by the various ioctl(2) calls. The naming convention of the fields for the various USB descriptors exactly follows the naming in the USB specification. Byte sized fields can be accessed directly, but word (16-bit) sized fields must be accessed by the (field) and (field, value) macros and double word (32-bit) sized fields must be accessed by the (field) and (field, value) macros to handle byte order and alignment properly.

The include file <dev/usb/usbhid.h> similarly contains the definitions for Human Interface Devices (HID).

usbhidaction(1), usbhidctl(1), ioctl(2), dwctwo(4), ehci(4), ohci(4), uhci(4), xhci(4), config(8), usbdevs(8)

The USB specifications can be found at

The usb driver appeared in OpenBSD 2.6.

March 27, 2019 OpenBSD-6.5