| USB(4) | Device Drivers Manual | USB(4) |
usb, uhub —
introduction 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?
option USBVERBOSE
#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.
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:
portconfigurationinterfacevendorproductreleaseThe 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:
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:
USB_DEVICEINFO
struct usb_device_info#define USB_MAX_DEVNAMES 4
#define USB_MAX_DEVNAMELEN 16
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
#define USB_SPEED_SUPER 4
u_int8_t udi_port;
int udi_power; /* power consumption */
int udi_nports;
char udi_devnames[USB_MAX_DEVNAMES]
[USB_MAX_DEVNAMELEN];
u_int32_t udi_ports[16]; /* hub only */
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.
USB_DEVICESTATS
struct usb_device_statsstruct 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.
USB_DEVICE_GET_DDESC
struct usb_device_ddescstruct 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.
USB_DEVICE_GET_CDESC
struct usb_device_cdescUSB_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.
USB_DEVICE_GET_FDESC
struct usb_device_fdescUSB_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.
USB_REQUEST
struct usb_ctl_requestThe 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
UGETW(field)
and
USETW(field,
value) macros and double word (32-bit) sized fields
must be accessed by the
UGETDW(field)
and
USETDW(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: https://www.usb.org/documents
The usb driver appeared in
OpenBSD 2.6.
| March 13, 2021 | OpenBSD-current |