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UGEN(4) FreeBSD Kernel Interfaces Manual UGEN(4)
NAME ugen - USB generic device support
SYNOPSIS ugen is integrated into the usb(4) kernel module.
DESCRIPTION The ugen driver provides support for all USB devices that do not have a special driver. It supports access to all parts of the device, but not in a way that is as convenient as a special purpose driver.
There can be up to 127 USB devices connected to a USB bus. Each USB device can have up to 16 endpoints. Each of these endpoints will communicate in one of four different modes: control, isochronous, bulk, or interrupt. Each of the endpoints will have a different device node. The four least significant bits in the minor device number determine which endpoint the device accesses, and the rest of the bits determine which USB device.
If an endpoint address is used both for input and output, the device can be opened for both read or write.
To find out which endpoints exist, there are a series of ioctl(2) operations on the control endpoint that return the USB descriptors of the device, configurations, interfaces, and endpoints.
The control transfer mode can only happen on the control endpoint which is always endpoint 0. The control endpoint accepts a request and may respond with an answer to such a request. Control requests are issued by ioctl(2) calls.
The bulk transfer mode can be in or out depending on the endpoint. To perform I/O on a bulk endpoint read(2) and write(2) should be used. All I/O operations on a bulk endpoint are unbuffered.
The interrupt transfer mode can be in or out depending on the endpoint. To perform I/O on an interrupt endpoint read(2) and write(2) should be used. A moderate amount of buffering is done by the driver.
All endpoints handle the following ioctl(2) calls:
USB_SET_SHORT_XFER (int) Allow short read transfer. Normally a transfer from the device which is shorter than the request specified is reported as an error.
USB_SET_TIMEOUT (int) Set the timeout on the device operations The time is specified in milliseconds. The value 0 is used to indicate that there is no timeout.
The control endpoint (endpoint 0) handles the following ioctl(2) calls:
USB_GET_CONFIG (int) Get the device configuration number.
USB_SET_CONFIG (int) given index. The uai_config_index is ignored in this call.
struct usb_alt_interface { int uai_config_index; int uai_interface_index; int uai_alt_no; };
USB_SET_ALTINTERFACE (struct usb_alt_interface) Set the alternative setting to the given number in the interface with the given index. The uai_config_index is ignored in this call.
This operation can only be performed when no endpoints for the interface are open.
USB_GET_NO_ALT (struct usb_alt_interface) Return the number of different alternate settings in the uai_alt_no field.
USB_GET_DEVICE_DESC (usb_device_descriptor_t) Return the device descriptor.
USB_GET_CONFIG_DESC (struct usb_config_desc) Return the descriptor for the configuration with the given index. For convenience, the current configuration can be specified by USB_CURRENT_CONFIG_INDEX.
struct usb_config_desc { int ucd_config_index; usb_config_descriptor_t ucd_desc; };
USB_GET_INTERFACE_DESC (struct usb_interface_desc) Return the interface descriptor for an interface specified by its configuration index, interface index, and alternative index. For convenience, the current alternative can be specified by USB_CURRENT_ALT_INDEX.
struct usb_interface_desc { int uid_config_index; int uid_interface_index; int uid_alt_index; usb_interface_descriptor_t uid_desc; };
USB_GET_ENDPOINT_DESC (struct usb_endpoint_desc) Return the endpoint descriptor for the endpoint specified by its configuration index, interface index, alternative index, and endpoint index.
struct usb_endpoint_desc { int ued_config_index; int ued_interface_index; int ued_alt_index; int ued_endpoint_index; usb_endpoint_descriptor_t ued_desc; };
}; The ufd_data field should point to a memory area of the size given in the ufd_size field. The proper size can be determined by first issuing a USB_GET_CONFIG_DESC and inspecting the wTotalLength field.
USB_GET_STRING_DESC (struct usb_string_desc) Get a string descriptor for the given language ID and string index.
struct usb_string_desc { int usd_string_index; int usd_language_id; usb_string_descriptor_t usd_desc; };
USB_DO_REQUEST (struct usb_ctl_request) Send a USB request to the device on the control endpoint. Any data sent to/from the device is located at ucr_data. The size of the transferred data is determined from the ucr_request. The ucr_addr field is ignored in this call. The ucr_flags field can be used to flag that the request is allowed to be shorter than the requested size, and ucr_actlen will contain the actual size on completion.
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 */ }; This is a dangerous operation in that it can perform arbitrary operations on the device. Some of the most dangerous (e.g., changing the device address) are not allowed.
USB_GET_DEVICEINFO (struct usb_device_info) Get an information summary for the device. This call will not issue any USB transactions.
Note that there are two different ways of addressing configurations, interfaces, alternatives, and endpoints: by index or by number. The index is the ordinal number (starting from 0) of the descriptor as presented by the device. The number is the respective number of the entity as found in its descriptor. Enumeration of descriptors uses the index, getting and setting typically uses numbers.
Example: all endpoints (except the control endpoint) for the current configuration can be found by iterating the interface_index from 0 to config_desc->bNumInterface-1 and for each of these, iterating the endpoint_index from 0 to interface_desc->bNumEndpoints. The config_index should be set to USB_CURRENT_CONFIG_INDEX and alt_index should be set to USB_CURRENT_ALT_INDEX.
SYSCTL VARIABLES The following variables are available as both sysctl(8) variables and loader(8) tunables:

SEE ALSO usb(4)
HISTORY The ugen driver appeared in NetBSD 1.4.
FreeBSD 14.0-RELEASE-p11 May 14, 2021 FreeBSD 14.0-RELEASE-p11