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.Dd July 12, 1998 .Dt UGEN 4 .Os .Sh NAME .Nm ugen .Nd USB generic device support .Sh SYNOPSIS .Cd "ugen* at uhub? port ?"
p .Sh DESCRIPTION The .Nm 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.
p 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. The four least significant bits in the minor device number determines which endpoint the device access and the rest of the bits determines the device.
p To find out what endpoints that exist there are a series of .Xr ioctl 2 operation on the control endpoint that returns the USB descriptors of the device, configuration, interface, etc.
p The control transfer mode can only happen on the control endpoint which is always endpoint 0. The control endpoint accepts request and may respond with an answer to such request. Control request are issued by .Xr ioctl 2 calls.
p The isochronous transfer mode can be in or out depending on the endpoint. To perform IO on an isochronous endpoint .Xr read 2 and .Xr write 2 should be used. Before any IO operations can take place the transfer rate in bytes/second has to be set. This is done with .Xr ioctl 2 .Dv USB_SET_ISO_RATE . Performing this call sets up a buffer corresponding to about 1 second of data.
p The bulk transfer mode can be in or out depending on the endpoint. To perform IO on a bulk endpoint .Xr read 2 and .Xr write 2 should be used. All IO operations on a bulk endpoint are unbuffered.
p The interrupt transfer mode can only be in. To perform input from an interrupt endpoint .Xr read 2 should be used. A certain moderate amount of buffering is done by the driver.
p The .Xr select 2 call can be used on all endpoint except the control endpoint. .Sh SEE ALSO .Xr usb 4 .Sh HISTORY The .Nm driver appeared in .Nx 1.4 .