Updated: 2022/Sep/29

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UGEN(4)                      Device Drivers Manual                     UGEN(4)

     ugen - USB generic device support

     ugen* at uhub? flags N
     ugen* at uhub? vendor V product P flags 1
     ugenif* at uhub? vendor V product P configuration C interface I

     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.

     Normally the ugen driver is used when no other driver attaches to a
     device.  If "flags 1" is specified, the ugen will instead attach with a
     very high priority and always be used.  Together with the vendor and
     product locators this can be used to force the ugen driver to be used for
     a certain device.

     The second form of attachment can be used to "steal" only one interface
     from some device for use by the ugen driver.  Most likely you want to
     explicitly specify at least vendor, product and interface with this form,
     as otherwise the ugen driver would capture all of your usb devices.
     NOTE: You have to be extremely careful, when using this form, as the
     attached ugen driver has access to all of the device and can easily
     interfere with the driver(s) used for the other interface(s).

     As an example of this second form of attachment there are various
     debugging boards available based on some FTDI chip, where one interface
     is used for JTAG debugging and the other is used as a serial interface.
     In this case you want to attach the ugen driver to interface 0 of this
     particular board identified by vendor and product while letting uftdi(4)
     together with ucom(4) to attach at interface 1.

     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 determines
     which endpoint the device accesses and the rest of the bits determines
     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 what 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 requests and may
     respond with an answer to such requests.  Control requests are issued by
     ioctl(2) calls.

     The bulk transfer mode can be in or out depending on the endpoint.  To
     perform IO on a bulk endpoint read(2) and write(2) should be used.  All
     IO operations on a bulk endpoint are normally unbuffered.  The
     USB_SET_BULK_RA and USB_SET_BULK_WB ioctl(2) calls enable read-ahead and
     write-behind buffering, respectively.  This buffering supports fixed-
     sized USB transfers and is intended for devices with regular and
     continuing data transfers.  When read-ahead or write-behind are enabled,
     the file descriptor may be set to use non-blocking IO.

     When in a read-ahead/writeback mode, select(2) for read and write
     operates normally, returning true if there is data in the read buffer and
     space in the write buffer, respectively.  When not, select(2) always
     returns true, because there is no way to predict how the device will
     respond to a read or write request.

     The interrupt transfer mode can be in or out depending on the endpoint.
     To perform IO 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:

             Allow short read transfer.  Normally a transfer from the device
             which is shorter than the request specified is reported as an
     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)
             Set the device into the given configuration number.

             This operation can only be performed when the control endpoint is
             the sole open endpoint.
     USB_GET_ALTINTERFACE (struct usb_alt_interface)
             Get the alternative setting number for the interface with the
             given index.  The 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

             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

             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

             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;
     USB_GET_FULL_DESC (struct usb_full_desc)
             Return all the descriptors for the given configuration.

             struct usb_full_desc {
                     int     ufd_config_index;
                     u_int   ufd_size;
                     u_char  *ufd_data;
             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

             struct usb_string_desc {
                     int     usd_string_index;
                     int     usd_language_id;
                     usb_string_descriptor_t usd_desc;
             Send a USB request to the device on the control endpoint.  Any
             data sent to/from the device is located at data.  The size of the
             transferred data is determined from the 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 the ucr_actlen field 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.

     Bulk endpoints handle the following ioctl(2) calls:

     USB_SET_BULK_RA (int)
             Enable or disable bulk read-ahead.  When enabled, the driver will
             begin to read data from the device into a buffer, and will
             perform reads from the device whenever there is room in the
             buffer.  The read(2) call will read data from this buffer,
             blocking if necessary until there is enough data to read the
             length of data requested.  The buffer size and the read request
             length can be set by the USB_SET_BULK_RA_OPT ioctl(2) call.
     USB_SET_BULK_WB (int)
             Enable or disable bulk write-behind.  When enabled, the driver
             will buffer data from the write(2) call before writing it to the
             device, enabling the write(2) call to return immediately.
             write(2) will block if there is not enough room in the buffer for
             all the data.  The buffer size and the write request length can
             be set by the USB_SET_BULK_WB_OPT ioctl(2) call.
     USB_SET_BULK_RA_OPT (struct usb_bulk_ra_wb_opt)
             Set the size of the buffer and the length of the read requests
             used by the driver when bulk read-ahead is enabled.  The changes
             do not take effect until the next time bulk read-ahead is
             enabled.  Read requests are made for the length specified, and
             the host controller driver (i.e., ehci(4), ohci(4), and uhci(4))
             will perform as many bus transfers as required.  If transfers
             from the device should be smaller than the maximum length,
             ra_wb_request_size must be set to the required length.

             struct usb_bulk_ra_wb_opt {
                     u_int   ra_wb_buffer_size;
                     u_int   ra_wb_request_size;
     USB_SET_BULK_WB_OPT (struct usb_bulk_ra_wb_opt)
             Set the size of the buffer and the length of the write requests
             used by the driver when bulk write-behind is enabled.  The
             changes do not take effect until the next time bulk write-behind
             is enabled.

     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 use 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 set to USB_CURRENT_CONFIG_INDEX and alt_index should be set to

     /dev/ugenN.EE                     Endpoint EE of device N.


     The ugen driver appeared in NetBSD 1.4.

NetBSD 10.99                  September 14, 2019                  NetBSD 10.99