PBUS(3)                                                   PBUS(3)

     NAME
          pbus - USR/3Com Edgeserver packet bus

     SYNOPSIS
          bind -a '#Y' /dev

          /dev/pbus
          /dev/pbusctl

     DESCRIPTION
          The packet bus driver serves a directory containing two
          files, giving MAC-level access to the EPB version of the
          packet bus of the US Robotics (3Com) Edgeserver chassis.

          The read-only file pbusctl contains a single integer that
          gives the chassis slot occupied by the Edge server (its
          address on the packet bus).

          The file pbus is read and written to communicate on the bus.
          Each write transmits a single packet on the bus.  The driver
          expects a four byte header in each write:

               slot chan 0 0

          where slot is the destination chassis slot number and chan
          identifies a logical receiver in that slot.  Including the
          header, the largest write accepted is 128 bytes.  The driver
          completes the header as the bus firmware requires; it also
          pads each packet with zero bytes to a hardware packet bound-
          ary as it puts it on the bus.  It flashes green in the `Wan
          TX' LED as packets are transmitted.

          Each read of the pbus file returns the contents of a single
          packet received from the bus.  The read will block if neces-
          sary until a packet arrives.  The data includes a four byte
          header as above, and padding to a hardware packet boundary.
          Normally a higher-level protocol will provide its own head-
          ers including an actual length.

          At reset, the driver downloads firmware to the controller if
          required.  All invalid packets received are quietly dis-
          carded.  Packets are also dropped whenever an internal input
          queue overflows because the reader has not kept up with
          arriving traffic.

     SOURCE
          /os/pc/devpbus.c

     SEE ALSO
          plap(3)

     PBUS(3)                                                   PBUS(3)

     BUGS
          The driver detects but does not recover from bus clock loss
          The driver cannot be included in the public distribution.