USB(3)                      (MPC823)                       USB(3)

          usb - USB device interface

          bind -a '#U' /dev


          The USB device serves a one-level directory, giving access
          to six files.  They provide an interface to the device
          (slave) mode of the 823/850 USB controller, allowing an
          Inferno system to provide services to the USB host.  The
          controller's endpoints are configured as follows.  Endpoint
          0 is the default USB control endpoint, as required by the
          USB standard.  Endpoint 1 responds to bulk output requests
          from the host; endpoint 2 responds to bulk input requests
          from the host; endpoint 3 is unused.

          The data file usbdata provides read and write access to end-
          points 1 and 2.  When the file is read, it returns data
          written to endpoint 1 by the USB host.  Data written to the
          file is provided in response to the host's read requests on
          endpoint 2.  Output data is converted to packets limited to
          the maximum packet length for the endpoint (see the maxpkt
          control request, below), which is 1023 bytes by default.
          Note that zero length records can be transmitted and
          received on USB.

          The file usbsetup provides read and write access to endpoint
          0.  When the file is read, it returns SETUP requests from
          the host.  If a given request requires a reply, the reply
          must be written to the file (host requests will automati-
          cally be NAKd until then).  Requests and replies are in
          binary form as defined in the USB specification, except for
          the reset message described below.  The driver itself inter-
          prets all SET_ADDRESS requests from the host, and sets the
          controller's address accordingly.  That request will there-
          fore not be visible on the usbsetup file.

          A USB bus or device reset sets the controller's USB address
          to zero, the USB `default address' for configuration.  It
          also resets all data toggles to DATA0.  A subsequent read of
          usbsetup will return the following special 8-byte reset mes-

     USB(3)                      (MPC823)                       USB(3)

               byte 16rFF, byte 16rFF, byte 'r', byte 'e',
               byte 's', byte 'e', byte 't', byte '\n'

          which does not resemble a normal SETUP message.  Further
          reads and writes on usbdata will return errors until that
          file has been closed and reopened.

          The control file usbctl receives textual commands to set
          device parameters and responses:

          maxpktn nb
               Set the maximum packet size for endpoint n to nb bytes.
               Nb must be between 8 and 64 bytes for the control end-
               point 0, and between 1 and 1023 bytes for the other
               endpoints.  The default is 8 bytes for endpoint 0 and
               1023 bytes for the others.

          rdtogn t
               Set the data toggle for input in endpoint n to t, which
               must be either 0 (DATA0) or 1 (DATA1).

               Cause endpoint n to respond to host IN and OUT tokens
               by stalling.

               Cancel the effect of a previous stall request on end-
               point n.

          wrtogn t
               Set the data toggle for the next packet output by end-
               point n to t, which must be either 0 (DATA0) or 1

          Stalling an endpoint causes IN and OUT transactions from the
          host to return a `stalled' error status.  On the control
          endpoint (endpoint 0), however, SETUP transactions will
          still arrive on usbsetup, and the arrival of a SETUP will
          automatically clear the `stalled' status for the endpoint,
          allowing an application to reject a control request (by
          stalling the subsequent status transaction) without stalling
          the control endpoint by rejecting subsequent SETUP transac-

          The status file usbstat is a read-only file, containing one
          line of statistics for each endpoint, giving: endpoint num-
          ber; data toggles; maximum packet size; count of input and
          output bytes and packets; and counts of various error condi-

          The read-only file usbaddr contains a single number giving
          the current device address.

     USB(3)                      (MPC823)                       USB(3)

          The read-only file usbframe contains a single line giving
          the current USB frame number.