.TH PBUS 3.SH NAMEpbus \- USR/3Com Edgeserver packet bus.SH SYNOPSIS.B bind -a '#Y' /dev.PP.B /dev/pbus.br.B /dev/pbusctl.SH DESCRIPTIONThe packet bus driver serves a directory containing two files,giving MAC-level access to the EPB version of the packet busof the US Robotics (3Com) Edgeserver chassis..PPThe read-only file.B pbusctlcontains a single integer that gives the chassis slot occupied by the Edge server(its address on the packet bus)..PPThe file.B pbusis read and written to communicate on the bus.Each writetransmits a single packet on the bus.The driver expects a four byte header in each write:.IP.IB "slot chan" " 0 0".PPwhere.I slotis the destination chassis slot number and.I chanidentifies 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 boundaryas it puts it on the bus.It flashes green in the `Wan TX' LED as packets are transmitted..PPEach read of the.B pbusfile returns the contents of a single packet received from the bus.The read will block if necessary until a packet arrives.The data includes a four byte headeras above, and padding to a hardware packet boundary.Normally a higher-level protocol will provide its own headers includingan actual length..PPAt reset, the driver downloads firmware to the controller if required.All invalid packets received are quietly discarded.Packets are also dropped whenever an internal input queue overflowsbecause the reader has not kept up with arriving traffic..SH SOURCE.B /os/pc/devpbus.c.SH SEE ALSO.IR plap (3).SH BUGSThe driver detects but does not recover from bus clock loss.brThe driver cannot be included in the public distribution.