1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)ec.4 8.1 (Berkeley) 6/5/93 33.\" 34.Dd June 5, 1993 35.Dt EC 4 vax 36.Os BSD 4.2 37.Sh NAME 38.Nm ec 39.Nd 3Com 10 Mb/s Ethernet interface 40.Sh SYNOPSIS 41.Cd "device ec0 at uba0 csr 161000 vector ecrint eccollide ecxint flags 0" 42.Sh DESCRIPTION 43The 44.Nm ec 45interface provides access to a 10 Mb/s Ethernet network through 46a 3com controller. 47.Pp 48The hardware has 32 kilobytes of dual-ported memory on the 49.Tn UNIBUS . 50This memory 51is used for internal buffering by the board, and the interface code reads 52the buffer contents directly through the 53.Tn UNIBUS . 54The address of this memory is given in the 55.Ar flags 56field 57in the configuration file. 58The first interface normally has its memory at Unibus address 0. 59.Pp 60Each of the host's network addresses 61is specified at boot time with an 62.Dv SIOCSIFADDR 63.Xr ioctl 2 . 64The 65.Nm ec 66interface employs the address resolution protocol described in 67.Xr arp 4 68to dynamically map between Internet and Ethernet addresses on the local 69network. 70.Pp 71The interface normally tries to use a 72.Dq trailer 73encapsulation 74to minimize copying data on input and output. 75The use of trailers is negotiated with 76.Tn ARP . 77This negotiation may be disabled, on a per-interface basis, 78by setting the 79.Dv IFF_NOTRAILERS 80flag with an 81.Dv SIOCSIFFLAGS 82.Xr ioctl . 83.Pp 84The interface software implements an exponential backoff algorithm 85when notified of a collision on the cable. This algorithm utilizes 86a 16-bit mask and the 87.Tn VAX-11 Ns 's 88interval timer in calculating a series 89of random backoff values. The algorithm is as follows: 90.Bl -enum -offset indent 91.It 92Initialize the mask to be all 1's. 93.It 94If the mask is zero, 16 retries have been made and we give 95up. 96.It 97Shift the mask left one bit and formulate a backoff by 98masking the interval timer with the smaller of the complement of this mask 99and a 5-bit mask, resulting in a pseudo-random number between 0 and 31. 100This produces the number of slot times to delay, 101where a slot is 51 microseconds. 102.It 103Use the value calculated in step 3 to delay before retransmitting 104the packet. 105The delay is done in a software busy loop. 106.El 107.Sh DIAGNOSTICS 108.Bl -diag 109.It ec%d: send error. 110After 16 retransmissions using the 111exponential backoff algorithm described above, the packet 112was dropped. 113.Pp 114.It ec%d: input error (offset=%d). 115The hardware indicated an error 116in reading a packet off the cable or an illegally sized packet. 117The buffer offset value is printed for debugging purposes. 118.Pp 119.It ec%d: can't handle af%d. 120The interface was handed 121a message with addresses formatted in an unsuitable address 122family; the packet was dropped. 123.El 124.Sh SEE ALSO 125.Xr netintro 4 , 126.Xr inet 4 , 127.Xr arp 4 128.Sh HISTORY 129The 130.Nm 131driver appeared in 132.Bx 4.2 . 133.Sh BUGS 134The hardware is not capable of talking to itself. The software 135implements local sending and broadcast by sending such packets to the 136loop interface. This is a kludge. 137.Pp 138Backoff delays are done in a software busy loop. This can degrade the 139system if the network experiences frequent collisions. 140