147 lines
4.6 KiB
Groff
147 lines
4.6 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)en.4 8.1 (Berkeley) 6/5/93
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.\"
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.Dd June 5, 1993
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.Dt EN 4 vax
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.Os BSD 4.2
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.Sh NAME
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.Nm en
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.Nd Xerox 3 Mb/s Ethernet interface
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.Sh SYNOPSIS
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.Cd "device en0 at uba0 csr 161000 vector enrint enxint encollide"
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.Sh DESCRIPTION
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The
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.Nm en
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interface provides access to a 3 Mb/s Ethernet network.
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Due to limitations in the hardware,
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.Tn DMA
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transfers
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to and from the network must take place in the lower 64K bytes
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of the
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.Tn UNIBUS
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address space, and thus this must be among the first
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.Tn UNIBUS
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devices enabled after boot.
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.Pp
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Each of the host's network addresses
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is specified at boot time with an
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.Dv SIOCSIFADDR
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.Xr ioctl 2 .
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The station address is discovered by probing the on-board Ethernet
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address register, and is used to verify the protocol addresses.
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No packets will be sent or accepted until
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a network address is supplied.
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.Pp
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The interface software implements an exponential backoff algorithm
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when notified of a collision on the cable. This algorithm utilizes
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a 16-bit mask and the
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.Tn VAX-11 Ns 's
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interval timer in calculating a series
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of random backoff values. The algorithm is as follows:
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.Pp
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.Bl -enum -offset indent
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.It
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Initialize the mask to be all 1's.
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.It
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If the mask is zero, 16 retries have been made and we give
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up.
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.It
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Shift the mask left one bit and formulate a backoff by
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masking the interval timer with the mask (this is actually
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the two's complement of the value).
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.It
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Use the value calculated in step 3 to delay before retransmitting
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the packet.
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.El
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.Pp
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The interface handles both Internet and
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.Tn NS
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protocol families.
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It normally tries to use a
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.Dq trailer
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encapsulation
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to minimize copying data on input and output.
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The use of trailers is negotiated with
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.Tn ARP .
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This negotiation may be disabled, on a per-interface basis,
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by setting the
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.Dv IFF_NOTRAILERS
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flag with an
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.Dv SIOCSIFFLAGS
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.Xr ioctl .
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.Sh DIAGNOSTICS
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.Bl -diag
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.It en%d: output error.
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The hardware indicated an error on
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the previous transmission.
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.Pp
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.It en%d: send error.
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After 16 retransmissions using the
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exponential backoff algorithm described above, the packet
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was dropped.
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.Pp
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.It en%d: input error.
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The hardware indicated an error
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in reading a packet off the cable.
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.Pp
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.It en%d: can't handle af%d.
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The interface was handed
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a message with addresses formatted in an unsuitable address
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family; the packet was dropped.
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.El
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.Sh SEE ALSO
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.Xr netintro 4 ,
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.Xr inet 4
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.Sh HISTORY
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The
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.Nm
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driver appeared in
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.Bx 4.2 .
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.Sh BUGS
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The device has insufficient buffering to handle back to
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back packets. This makes use in a production environment
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painful.
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.Pp
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The hardware does word at a time
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.Tn DMA
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without byte swapping.
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To compensate, byte swapping of user data must either be done
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by the user or by the system. A kludge to byte swap only
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.Tn IP
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packets is provided if the
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.Dv ENF_SWABIPS
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flag is defined in
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the driver and set at boot time with an
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.Dv SIOCSIFFLAGS
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.Xr ioctl .
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