ref: a920c765f2b4130590fb5971a50690b21664957a
dir: /man/3/pbus/
.TH PBUS 3 .SH NAME pbus \- USR/3Com Edgeserver packet bus .SH SYNOPSIS .B bind -a '#Y' /dev .PP .B /dev/pbus .br .B /dev/pbusctl .SH 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. .PP The read-only file .B pbusctl contains a single integer that gives the chassis slot occupied by the Edge server (its address on the packet bus). .PP The file .B 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: .IP .IB "slot chan" " 0 0" .PP where .I slot is the destination chassis slot number and .I 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 boundary as it puts it on the bus. It flashes green in the `Wan TX' LED as packets are transmitted. .PP Each read of the .B pbus file 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 header as above, and padding to a hardware packet boundary. Normally a higher-level protocol will provide its own headers including an actual length. .PP At 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 overflows because the reader has not kept up with arriving traffic. .SH SOURCE .B /os/pc/devpbus.c .SH SEE ALSO .IR plap (3) .SH BUGS The driver detects but does not recover from bus clock loss .br The driver cannot be included in the public distribution.