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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 ?"
.Pp
.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.
.Pp
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.
.Pp
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.
.Pp
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.  
.Pp
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.
.Pp
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.
.Pp
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.
.Pp
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 .
.Sh BUGS
The driver is not yet completed.