1.\" $NetBSD: en.4,v 1.10 2002/01/15 02:06:31 wiz Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" from: @(#)en.4 8.1 (Berkeley) 6/5/93 35.\" 36.Dd June 5, 1993 37.Dt EN 4 vax 38.Os 39.Sh NAME 40.Nm en 41.Nd Xerox 3 Mb/s Ethernet interface 42.Sh SYNOPSIS 43.Cd "en0 at uba0 csr 161000 vector enrint enxint encollide" 44.Sh DESCRIPTION 45NOTE: This driver has not been ported from 46.Bx 4.4 47yet. 48.Pp 49The 50.Nm en 51interface provides access to a 3 Mb/s Ethernet network. 52Due to limitations in the hardware, 53.Tn DMA 54transfers 55to and from the network must take place in the lower 64K bytes 56of the 57.Tn UNIBUS 58address space, and thus this must be among the first 59.Tn UNIBUS 60devices enabled after boot. 61.Pp 62Each of the host's network addresses 63is specified at boot time with an 64.Dv SIOCSIFADDR 65.Xr ioctl 2 . 66The station address is discovered by probing the on-board Ethernet 67address register, and is used to verify the protocol addresses. 68No packets will be sent or accepted until 69a network address is supplied. 70.Pp 71The interface software implements an exponential backoff algorithm 72when notified of a collision on the cable. This algorithm utilizes 73a 16-bit mask and the 74.Tn VAX-11 Ns 's 75interval timer in calculating a series 76of random backoff values. The algorithm is as follows: 77.Pp 78.Bl -enum -offset indent 79.It 80Initialize the mask to be all 1's. 81.It 82If the mask is zero, 16 retries have been made and we give 83up. 84.It 85Shift the mask left one bit and formulate a backoff by 86masking the interval timer with the mask (this is actually 87the two's complement of the value). 88.It 89Use the value calculated in step 3 to delay before retransmitting 90the packet. 91.El 92.Pp 93The interface handles both Internet and 94.Tn NS 95protocol families. 96It normally tries to use a 97.Dq trailer 98encapsulation 99to minimize copying data on input and output. 100The use of trailers is negotiated with 101.Tn ARP . 102This negotiation may be disabled, on a per-interface basis, 103by setting the 104.Dv IFF_NOTRAILERS 105flag with an 106.Dv SIOCSIFFLAGS 107.Xr ioctl 2 . 108.Sh DIAGNOSTICS 109.Bl -diag 110.It en%d: output error. 111The hardware indicated an error on 112the previous transmission. 113.Pp 114.It en%d: send error. 115After 16 retransmissions using the 116exponential backoff algorithm described above, the packet 117was dropped. 118.Pp 119.It en%d: input error. 120The hardware indicated an error 121in reading a packet off the cable. 122.Pp 123.It en%d: can't handle af%d. 124The interface was handed 125a message with addresses formatted in an unsuitable address 126family; the packet was dropped. 127.El 128.Sh SEE ALSO 129.Xr inet 4 , 130.Xr netintro 4 131.Sh HISTORY 132The 133.Nm 134driver appeared in 135.Bx 4.2 . 136.Sh BUGS 137The device has insufficient buffering to handle back to 138back packets. This makes use in a production environment 139painful. 140.Pp 141The hardware does word at a time 142.Tn DMA 143without byte swapping. 144To compensate, byte swapping of user data must either be done 145by the user or by the system. A kludge to byte swap only 146.Tn IP 147packets is provided if the 148.Dv ENF_SWABIPS 149flag is defined in 150the driver and set at boot time with an 151.Dv SIOCSIFFLAGS 152.Xr ioctl 2 . 153