.SH
9P Protocol Drivers
.PP
The file server described so far
waits for 9P protocol messages to
appear in its input queue.
It processes each message and
sends the reply back to the originator.
There are groups of processes that
perform protocol I/O on some network or
device and the resulting messages
are sent to the file system queue.
The simplest of these is the driver
for the Cyclone I/O board.
The Cyclone is a fiber machine-to-machine
interface on a VME bus.
Each Cyclone board has an i960 computer on it.
The i960 can do DMA transfers on the VME bus
and can transmit and receive bytes over its
fiber interface.
The microcode on the i960 manages a set of
buffers in the host memory.
When a 9P message arrives on the fiber interface,
the message is transferred into the host memory
and placed in circular queue of buffers.
The cyclone also has a circular queue of
messages to transmit.
The transfer rate averages about a megabyte per second and
the latency is a few microseconds for a small
message.
Almost no protocol is involved.
It is possible to checksum the messages,
but there is such a low error rate that it
has been disabled.
.PP
There are two Cyclones on Bootes.
One interface goes to our main CPU server
while the other is not used.
.PP
There is a set of two processes
.CW lai
and
.CW lao
that perform Ethernet input and output.
These processes send Ethernet messages
to/from two more processes
.CW ilo
and
.CW ilt
that do the IL reliable datagram protocol
on top of IP packets.
.PP
There is another suite of five processes
.CW dki ,
.CW dko ,
.CW dkp ,
.CW dkt ,
and
.CW dkl
that do the Datakit URP protocol on top of a
Datakit device driver.
The structure is such that more protocol
stacks can be added to feed the file system.
.PP
The last process in Bootes,
.CW con ,
reads the console
and calls internal subroutines to
executes commands typed.
Since there is only one process,
only one command can be executing at a
time.
See
.I fs (8)
for a description of the
commands available at the console.